Discussion:
Why not use crankshaft weights on any vee engine?
(too old to reply)
w***@yahoo.com
2008-11-25 02:45:04 UTC
Permalink
Hi - I'm trying figure out if crankshaft counterweights can be
effectively used on other engines besides 90 degree v8s with
crossplane cranks.

In reading about crossplane v8s, it is explained that the crankshaft
causes pistons to go in opposite directions at each end of the engine
which would normally cause the engine to rock. This is supposed to be
counteracted by using crankshaft weight to balance each pair of
pistons.

In the diagrams that I have seen, this arrangement of a counterweight
works nicely with two pistons that are 90 degrees from each other.
That is, the side-to-side motion of the weight falls in the plane of
the other piston, so the weight is always cancelling one of the
pistons and is not causing extra vibration by itself.

The diagram typically just shows two pistons. My question is then,
why can't the counterweight system be used for any number of cylinders
as long as they are in a 90 degree vee?

I've often seen that the v6 is notoriously hard to balance. Why not
make a crank with 3 throws that are 120 degrees apart and have 3 pairs
of pistons (each pair connected to the same throw) and have
counterweights that will balance each pair? Since you've balanced
each pair, you should not have to worry about the engine rocking, just
as the rocking was corrected in the crossplane v8.

Of course, you wouldn't want to use counterweights on an engine that
really doesn't require it (eg V12).

Now I know I'm missing something, otherwise this would have been done
already. What am I missing?
Steve W.
2008-11-25 03:15:45 UTC
Permalink
Post by w***@yahoo.com
Hi - I'm trying figure out if crankshaft counterweights can be
effectively used on other engines besides 90 degree v8s with
crossplane cranks.
In reading about crossplane v8s, it is explained that the crankshaft
causes pistons to go in opposite directions at each end of the engine
which would normally cause the engine to rock. This is supposed to
be counteracted by using crankshaft weight to balance each pair of
pistons.
In the diagrams that I have seen, this arrangement of a counterweight
works nicely with two pistons that are 90 degrees from each other.
That is, the side-to-side motion of the weight falls in the plane of
the other piston, so the weight is always cancelling one of the
pistons and is not causing extra vibration by itself.
The diagram typically just shows two pistons. My question is then,
why can't the counterweight system be used for any number of
cylinders as long as they are in a 90 degree vee?
Uh it IS. Counterweights are used on just about every type of engine.
Either on the crankshaft itself or attached to the crankshaft externally
such as a weighted flywheel.
Post by w***@yahoo.com
I've often seen that the v6 is notoriously hard to balance. Why not
make a crank with 3 throws that are 120 degrees apart and have 3
pairs of pistons (each pair connected to the same throw) and have
counterweights that will balance each pair? Since you've balanced
each pair, you should not have to worry about the engine rocking,
just as the rocking was corrected in the crossplane v8.
Uh that has been done since about 1964.
Post by w***@yahoo.com
Of course, you wouldn't want to use counterweights on an engine that
really doesn't require it (eg V12).
They are already there.
Post by w***@yahoo.com
Now I know I'm missing something, otherwise this would have been done
already. What am I missing?
I have yet to see any crankshaft (other than a simple flat 4 or 6) that
didn't have counterweights. Many even use balance shafts to cancel out
the rocking coupling that occurs in the engines.

http://www.vincelewis.net/bigengine.html Has a bolt on external weight.
Loading Image...
--
Steve W.
Near Cooperstown, New York
w***@yahoo.com
2008-11-25 04:09:12 UTC
Permalink
Post by Steve W.
Post by w***@yahoo.com
Hi - I'm trying figure out if crankshaft counterweights can be
effectively used on other engines besides 90 degree v8s with
crossplane cranks.
In reading about crossplane v8s, it is explained that the crankshaft
causes pistons to go in opposite directions at each end of the engine
which would normally cause the engine to rock. This is supposed to
be counteracted by using crankshaft weight to balance each pair of
pistons.
In the diagrams that I have seen, this arrangement of a counterweight
works nicely with two pistons that are 90 degrees from each other.
That is, the side-to-side motion of the weight falls in the plane of
the other piston, so the weight is always cancelling one of the
pistons and is not causing extra vibration by itself.
The diagram typically just shows two pistons. My question is then,
why can't the counterweight system be used for any number of
cylinders as long as they are in a 90 degree vee?
Uh it IS. Counterweights are used on just about every type of engine.
Either on the crankshaft itself or attached to the crankshaft externally
such as a weighted flywheel.
Post by w***@yahoo.com
I've often seen that the v6 is notoriously hard to balance. Why not
make a crank with 3 throws that are 120 degrees apart and have 3
pairs of pistons (each pair connected to the same throw) and have
counterweights that will balance each pair? Since you've balanced
each pair, you should not have to worry about the engine rocking,
just as the rocking was corrected in the crossplane v8.
Uh that has been done since about 1964.
Post by w***@yahoo.com
Of course, you wouldn't want to use counterweights on an engine that
really doesn't require it (eg V12).
They are already there.
Post by w***@yahoo.com
Now I know I'm missing something, otherwise this would have been done
already. What am I missing?
I have yet to see any crankshaft (other than a simple flat 4 or 6) that
didn't have counterweights. Many even use balance shafts to cancel out
the rocking coupling that occurs in the engines.
http://www.vincelewis.net/bigengine.html Has a bolt on external weight.http://images.vetteweb.com/tech/vemp_0712w_27_z+2009_corvette_ZR1_LS9...
--
Steve W.
Near Cooperstown, New York
Thanks for the reply.
From what I can see from the pictures you attached...
The v8 crank is a crossplane crank which, by definition, has
counterweights.
The big inline engine, as far as I can see, has no counterweights
(neat engine though).

I must be reading all the wrong articles. From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons. Rather the pistons get primary
dynamic balancing from each other.

You mentioned that many engines use balance shafts. That is my
primary question. If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
Tegger
2008-11-25 05:10:34 UTC
Permalink
***@yahoo.com wrote in news:322e03f7-3462-440d-8d81-***@q9g2000yqc.googlegroups.com:

.
Post by w***@yahoo.com
Thanks for the reply.
From what I can see from the pictures you attached...
The v8 crank is a crossplane crank which, by definition, has
counterweights.
The big inline engine, as far as I can see, has no counterweights
(neat engine though).
I must be reading all the wrong articles. From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons. Rather the pistons get primary
dynamic balancing from each other.
The L4 and L6 crankshafts I've seen all have great big counterweights on
them. Even the L6 crank from some 1940's vehicle a neighbor is using as his
mailbox post (that one must have been a monster, with the size of the
journals it has).
Post by w***@yahoo.com
You mentioned that many engines use balance shafts. That is my
primary question. If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
It has to do with movement of the center of reciprocating mass. If the mass
is too great, this "primary couple" results in a vibration which is
objectionable and must be damped via an opposing imbalance. That's the
purpose of balance shafts.
http://en.wikipedia.org/wiki/V6
--
Tegger
Steve W.
2008-11-25 19:41:37 UTC
Permalink
Post by Tegger
.
Post by w***@yahoo.com
Thanks for the reply.
From what I can see from the pictures you attached...
The v8 crank is a crossplane crank which, by definition, has
counterweights.
The big inline engine, as far as I can see, has no counterweights
(neat engine though).
I must be reading all the wrong articles. From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons. Rather the pistons get primary
dynamic balancing from each other.
The L4 and L6 crankshafts I've seen all have great big counterweights on
them. Even the L6 crank from some 1940's vehicle a neighbor is using as his
mailbox post (that one must have been a monster, with the size of the
journals it has).
Lot's of the early engines had huge parts compared to current designs.
They ran at much lower rpms and were usually HEAVY with lots of iron.
Takes a stout crank to handle those iron pistons that were common.
Working on some of them makes you REALLY think about the guys who raced
them and worked on them to make them run.
Post by Tegger
Post by w***@yahoo.com
You mentioned that many engines use balance shafts. That is my
primary question. If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
It has to do with movement of the center of reciprocating mass. If the mass
is too great, this "primary couple" results in a vibration which is
objectionable and must be damped via an opposing imbalance. That's the
purpose of balance shafts.
http://en.wikipedia.org/wiki/V6
--
Steve W.
Near Cooperstown, New York

Life is not like a box of chocolates
it's more like a jar of jalapenos-
what you do today could burn your ass tomorrow!
Steve
2008-11-25 17:58:00 UTC
Permalink
Post by w***@yahoo.com
I must be reading all the wrong articles. From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons. Rather the pistons get primary
dynamic balancing from each other.
While its true that some engine layouts allow the crankshaft to be
balanced independent of the bob-weight of the pistons (inline-six for
example) it is NOT done without counter-weights. See the picture of the
Slant-6 and Jeep 258 inline six cranks I put in a previous post. In a
v8, the crank and pistons have to be balanced together.
Post by w***@yahoo.com
You mentioned that many engines use balance shafts. That is my
primary question. If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
You're missing the point. Balance shafts are used (primarily) on
inline-4 cylinder engines. Inline-4s HAVE primary balance through crank
counterweights! The problem is that it is impossible to eliminate a
*second* order imbalance on an inline 4 strictly through counterweights.
When you get perfect primary balance, you wind up with a residual 2nd
order imbalance that causes the engine to "jump" up and down along the
stroke axis at twice the crankshaft speed, because the center of mass of
the rotating assembly shifts up and down slightly twice per crank
rotation. The only way to damp that is with balance shafts spinning at
twice the crankshaft speed.

Now, another application of balance shafts is a certain *class* of v6
engine: namely, a v6 built using the same infrastructure as a v8 for
cost savings. These are usually rather low-RPM torque oriented v6
engines mainly for pickup truck applications, although there are others.
Common examples in production today include the Chevy Vortec v6 based
on the smallblock Chevy v8 casting, the Chrysler 3.7L v6 based on the
4.7L v8, and one of the many Ford 3.8 v6s which happens to be based on
the old Windsor v8. Those engines are peculiar in that they don't use
the "natural" 60-degree bank angle of a v6, and instead use the
90-degree bank angle that is natural to the parent v8. So for the v6
the crank journals have to be splayed. The splaying is always a
compromise between balance and even-firing, so there is some residual
imbalance that shafts can at least partially correct.

SIXTY-degree v6 engines don't use balance shafts.

I can also think of at least one inverse to the above case: The
Yamaha/Ford v8 used in the last generation Taurus SHO was a sixty-degree
v8, grown from a parent v6 casting. I don't remember if it had balance
shafts or not, it might have been small enough to get away without them.
ben91932
2009-01-08 02:48:49 UTC
Permalink
Post by Steve
I must be reading all the wrong articles.  From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons.  Rather the pistons get primary
dynamic balancing from each other.
While its true that some engine layouts allow the crankshaft to be
balanced independent of the bob-weight of the pistons (inline-six for
example) it is NOT done without counter-weights. See the picture of the
Slant-6 and Jeep 258 inline six cranks I put in a previous post. In a
v8, the crank and pistons have to be balanced together.
You mentioned that many engines use balance shafts.  That is my
primary question.  If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
You're missing the point. Balance shafts are used (primarily) on
inline-4 cylinder engines. Inline-4s HAVE primary balance through crank
counterweights! The problem is that it is impossible to eliminate a
*second* order imbalance on an inline 4 strictly through counterweights.
Now, another application of balance shafts is a certain *class* of v6
engine: namely, a v6 built using the same infrastructure as a v8 for
cost savings. These are usually rather low-RPM torque oriented v6
engines mainly for pickup truck applications, although there are others.
  Common examples in production today include the Chevy Vortec v6 based
on the smallblock Chevy v8 casting, the Chrysler 3.7L v6 based on the
4.7L v8, and one of the many Ford 3.8 v6s which happens to be based on
the old Windsor v8.  Those engines are peculiar in that they don't use
the "natural" 60-degree bank angle of a v6, and instead use the
90-degree bank angle that is natural to the parent v8.  So for the v6
the crank journals have to be splayed. The splaying is always a
compromise between balance and even-firing, so there is some residual
imbalance that shafts can at least partially correct.
SIXTY-degree v6 engines don't use balance shafts.
I can also think of at least one inverse to the above case: The
Yamaha/Ford v8 used in the last generation Taurus SHO was a sixty-degree
v8, grown from a parent v6 casting. I don't remember if it had balance
shafts or not, it might have been small enough to get away without them.
ben91932
2009-01-09 00:02:29 UTC
Permalink
Taurus 3.0's and later SHO's have balance shafts....
Post by Steve
SIXTY-degree v6 engines don't use balance shafts.
I can also think of at least one inverse to the above case: The
Yamaha/Ford v8 used in the last generation Taurus SHO was a sixty-degree
v8, grown from a parent v6 casting. I don't remember if it had balance
shafts or not, it might have been small enough to get away without them.
Steve W.
2008-11-25 19:48:17 UTC
Permalink
Post by w***@yahoo.com
Post by Steve W.
Post by w***@yahoo.com
Hi - I'm trying figure out if crankshaft counterweights can be
effectively used on other engines besides 90 degree v8s with
crossplane cranks.
In reading about crossplane v8s, it is explained that the crankshaft
causes pistons to go in opposite directions at each end of the engine
which would normally cause the engine to rock. This is supposed to
be counteracted by using crankshaft weight to balance each pair of
pistons.
In the diagrams that I have seen, this arrangement of a counterweight
works nicely with two pistons that are 90 degrees from each other.
That is, the side-to-side motion of the weight falls in the plane of
the other piston, so the weight is always cancelling one of the
pistons and is not causing extra vibration by itself.
The diagram typically just shows two pistons. My question is then,
why can't the counterweight system be used for any number of
cylinders as long as they are in a 90 degree vee?
Uh it IS. Counterweights are used on just about every type of engine.
Either on the crankshaft itself or attached to the crankshaft externally
such as a weighted flywheel.
Post by w***@yahoo.com
I've often seen that the v6 is notoriously hard to balance. Why not
make a crank with 3 throws that are 120 degrees apart and have 3
pairs of pistons (each pair connected to the same throw) and have
counterweights that will balance each pair? Since you've balanced
each pair, you should not have to worry about the engine rocking,
just as the rocking was corrected in the crossplane v8.
Uh that has been done since about 1964.
Post by w***@yahoo.com
Of course, you wouldn't want to use counterweights on an engine that
really doesn't require it (eg V12).
They are already there.
Post by w***@yahoo.com
Now I know I'm missing something, otherwise this would have been done
already. What am I missing?
I have yet to see any crankshaft (other than a simple flat 4 or 6) that
didn't have counterweights. Many even use balance shafts to cancel out
the rocking coupling that occurs in the engines.
http://www.vincelewis.net/bigengine.html Has a bolt on external weight.http://images.vetteweb.com/tech/vemp_0712w_27_z+2009_corvette_ZR1_LS9...
--
Steve W.
Near Cooperstown, New York
Thanks for the reply.
From what I can see from the pictures you attached...
The v8 crank is a crossplane crank which, by definition, has
counterweights.
And other than the throws looks like every other crankshaft out there.
Counterweights are there on virtually EVERY engine.
Post by w***@yahoo.com
The big inline engine, as far as I can see, has no counterweights
(neat engine though).
Look at the "flywheel" it has on it. That IS the counterweight.
Post by w***@yahoo.com
I must be reading all the wrong articles. From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons. Rather the pistons get primary
dynamic balancing from each other.
You mentioned that many engines use balance shafts. That is my
primary question. If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
The balance shafts are NOT for primary balancing. They are to counter a
rocking couple in the V engines and the vertical motion in the inlines.
--
Steve W.
Near Cooperstown, New York

Life is not like a box of chocolates
it's more like a jar of jalapenos-
what you do today could burn your ass tomorrow!
w***@yahoo.com
2008-11-26 02:05:33 UTC
Permalink
Post by Steve W.
Post by w***@yahoo.com
Post by Steve W.
Post by w***@yahoo.com
Hi - I'm trying figure out if crankshaft counterweights can be
effectively used on other engines besides 90 degree v8s with
crossplane cranks.
In reading about crossplane v8s, it is explained that the crankshaft
causes pistons to go in opposite directions at each end of the engine
which would normally cause the engine to rock. This is supposed to
be counteracted by using crankshaft weight to balance each pair of
pistons.
In the diagrams that I have seen, this arrangement of a counterweight
works nicely with two pistons that are 90 degrees from each other.
That is, the side-to-side motion of the weight falls in the plane of
the other piston, so the weight is always cancelling one of the
pistons and is not causing extra vibration by itself.
The diagram typically just shows two pistons. My question is then,
why can't the counterweight system be used for any number of
cylinders as long as they are in a 90 degree vee?
Uh it IS. Counterweights are used on just about every type of engine.
Either on the crankshaft itself or attached to the crankshaft externally
such as a weighted flywheel.
Post by w***@yahoo.com
I've often seen that the v6 is notoriously hard to balance. Why not
make a crank with 3 throws that are 120 degrees apart and have 3
pairs of pistons (each pair connected to the same throw) and have
counterweights that will balance each pair? Since you've balanced
each pair, you should not have to worry about the engine rocking,
just as the rocking was corrected in the crossplane v8.
Uh that has been done since about 1964.
Post by w***@yahoo.com
Of course, you wouldn't want to use counterweights on an engine that
really doesn't require it (eg V12).
They are already there.
Post by w***@yahoo.com
Now I know I'm missing something, otherwise this would have been done
already. What am I missing?
I have yet to see any crankshaft (other than a simple flat 4 or 6) that
didn't have counterweights. Many even use balance shafts to cancel out
the rocking coupling that occurs in the engines.
http://www.vincelewis.net/bigengine.htmlHas a bolt on external weight.http://images.vetteweb.com/tech/vemp_0712w_27_z+2009_corvette_ZR1_LS9...
--
Steve W.
Near Cooperstown, New York
Thanks for the reply.
From what I can see from the pictures you attached...
The v8 crank is a crossplane crank which, by definition, has
counterweights.
And other than the throws looks like every other crankshaft out there.
Counterweights are there on virtually EVERY engine.
Post by w***@yahoo.com
The big inline engine, as far as I can see, has no counterweights
(neat engine though).
Look at the "flywheel" it has on it. That IS the counterweight.
Post by w***@yahoo.com
I must be reading all the wrong articles. From what I've read, inline
4, straight 6, v12 , flat plane v8, (for example) do not use
counterweights to balance the pistons. Rather the pistons get primary
dynamic balancing from each other.
You mentioned that many engines use balance shafts. That is my
primary question. If you can achieve primary dynamic balancing on a
crossplane v8 using counterweights, why not use the weights on a v6
rather than an extra balancing shaft.
The balance shafts are NOT for primary balancing. They are to counter a
rocking couple in the V engines and the vertical motion in the inlines.
--
Steve W.
Near Cooperstown, New York
Life is not like a box of chocolates
it's more like a jar of jalapenos-
what you do today could burn your ass tomorrow!
I'm probably still not getting it, but back to the main question...
A crossplane v8 would normally have a terrible rocking motion because
the pistons at each end move in opposite direction. From what I
understand, the weights on each pair of pistons can completely balance
them. What makes a v8 special? Why can't any V (v2, v4, v6, v8) be
perfectly balanced in the same way? Or are you saying that these
engines can already be balanced like the crossplane v8 with weights
alone?

Again, I'm probably reading the wrong articles but I'm given to
understand that the counterweights on i4, i6, etc are only their to
balance the rotating stuff (the crank throw, part of the con rod,
etc), while the weights on a crossplane v8 are bigger and are designed
to cancel the pistons themselves. In other engines, this piston
cancellation is simply done by other pistons moving in the opposite
direction.
HLS
2008-11-26 04:56:09 UTC
Permalink
Post by w***@yahoo.com
Again, I'm probably reading the wrong articles but I'm given to
understand that the counterweights on i4, i6, etc are only their to
balance the rotating stuff (the crank throw, part of the con rod,
etc), while the weights on a crossplane v8 are bigger and are designed
to cancel the pistons themselves. In other engines, this piston
cancellation is simply done by other pistons moving in the opposite
direction.
There are several modes of vibration which are related to unbalanced
conditions.

The simplest countermeasures are those which attempt to balance the
piston/rod, etc
momentum versus the crank counterweight.

But the story doesnt stop here. nOrder vibrations are still possible, and
can be
irritating in an engine. The use of balance shafts doesnt mean that the
unbalance energy
is neutralized at the source.. it means that the engine as a system "sees"
the vibration
as a whole, and the balance shafts negate some of this energy... It can be
an amelioration
of the vibrational system, but not necessarily a neutralization of the
forces that caused
it.

Some people have suggested that all flat engines are inherently balanced..
Not so.
Some engines are said to be inherently balanceable, but one must take care
to realize
that n-order vibrations can come into effect.

Balance is not a simple concept, for most of us. That is why the more
serious balance
work is entertained by experts.
Tegger
2008-11-26 14:52:58 UTC
Permalink
Post by HLS
Balance is not a simple concept, for most of us. That is why the more
serious balance
work is entertained by experts.
Hypothetical question: Would a fork-and-blade, opposed, flat twin be the
most inherently balanced engine possible?
--
Tegger
Steve
2008-11-26 17:41:31 UTC
Permalink
Post by Tegger
Post by HLS
Balance is not a simple concept, for most of us. That is why the more
serious balance
work is entertained by experts.
Hypothetical question: Would a fork-and-blade, opposed, flat twin be the
most inherently balanced engine possible?
No, it would be maximally IMbalanced. A fork-and-blade approach is for
a pair of conrods sharing a journal and the came centerline (unlike a
typical car v8 where the conrods are side-by-side on a journal, and
therefore the banks are offset by 1/2 journal width). But in a 4-stroke
twin of any sort, you have to have the two pistons moving in unison so
that TDC exhaust/intake on one occurs at the same instant TDC combustion
on the other. For a flat twin, that means two separate journals on
opposite throws, meaning that the pistons move away from the crank at
the same time and then toward the crank at the same time. If you tried a
fork-and-blade setup, the imbalance would be HUGE because both pistons
would move "left" together, and then move "right" together.
Tegger
2008-11-26 18:06:27 UTC
Permalink
Post by Steve
Post by Tegger
Post by HLS
Balance is not a simple concept, for most of us. That is why the
more serious balance
work is entertained by experts.
Hypothetical question: Would a fork-and-blade, opposed, flat twin be
the most inherently balanced engine possible?
No, it would be maximally IMbalanced. A fork-and-blade approach is
for a pair of conrods sharing a journal and the came centerline
(unlike a typical car v8 where the conrods are side-by-side on a
journal, and therefore the banks are offset by 1/2 journal width). But
in a 4-stroke twin of any sort, you have to have the two pistons
moving in unison so that TDC exhaust/intake on one occurs at the same
instant TDC combustion on the other. For a flat twin, that means two
separate journals on opposite throws, meaning that the pistons move
away from the crank at the same time and then toward the crank at the
same time. If you tried a fork-and-blade setup, the imbalance would be
HUGE because both pistons would move "left" together, and then move
"right" together.
Silly me. What was I thinking? Of course the pistons in an opposed twin
would have to follow each other if they were connected to the same crank
journal.

I guess the only way you could have a balanced flat oppposed twin would be
if the crank had three connecting rod journals, with one of the pistons
having a forked connecting rod that attached to the two outside journals.
This way the pistons would oppose each others' forces, but they'd still
travel a common axis.
--
Tegger
Anumber1
2008-11-27 00:24:22 UTC
Permalink
Post by Steve
Post by Tegger
Post by HLS
Balance is not a simple concept, for most of us. That is why the more
serious balance
work is entertained by experts.
Hypothetical question: Would a fork-and-blade, opposed, flat twin be
the most inherently balanced engine possible?
No, it would be maximally IMbalanced. A fork-and-blade approach is for
a pair of conrods sharing a journal and the came centerline (unlike a
typical car v8 where the conrods are side-by-side on a journal, and
therefore the banks are offset by 1/2 journal width). But in a 4-stroke
twin of any sort, you have to have the two pistons moving in unison so
that TDC exhaust/intake on one occurs at the same instant TDC combustion
on the other. For a flat twin, that means two separate journals on
opposite throws, meaning that the pistons move away from the crank at
the same time and then toward the crank at the same time. If you tried a
fork-and-blade setup, the imbalance would be HUGE because both pistons
would move "left" together, and then move "right" together.
In a "just for thought" moment...

I think one of the balanced designs ever were the Fairbanks/Morse
opposed piston diesels of the late 1940's to be incredibly well
balanced. Unfortunately, the design did not lend itself to "easy" repair
of the lower cylinders and proved to be quite a maintenance hassle.

These engines were used in large boats/tugs/small ships and railroad
locomotives.

Balance of reciprocating weight is quite a bit more than it seems at
first glance.

Al
w***@yahoo.com
2008-11-27 00:44:41 UTC
Permalink
Post by Anumber1
Post by Steve
Post by Tegger
Post by HLS
Balance is not a simple concept, for most of us. That is why the more
serious balance
work is entertained by experts.
Hypothetical question: Would a fork-and-blade, opposed, flat twin be
the most inherently balanced engine possible?
No, it would be maximally IMbalanced. A fork-and-blade approach is for
a pair of conrods sharing a journal and the came centerline (unlike a
typical car v8 where the conrods are side-by-side on a journal, and
therefore the banks are offset by 1/2 journal width). But in a 4-stroke
twin of any sort, you have to have the two pistons moving in unison so
that TDC exhaust/intake on one occurs at the same instant TDC combustion
on the other. For a flat twin, that means two separate journals on
opposite throws, meaning that the pistons move away from the crank at
the same time and then toward the crank at the same time. If you tried a
fork-and-blade setup, the imbalance would be HUGE because both pistons
would move "left" together, and then move "right" together.
In a "just for thought" moment...
I think one of the balanced designs ever were the Fairbanks/Morse
opposed piston diesels of the late 1940's to be incredibly well
balanced. Unfortunately, the design did not lend itself to "easy" repair
of the lower cylinders and proved to be quite a maintenance hassle.
These engines were used in large boats/tugs/small ships and railroad
locomotives.
Balance of reciprocating weight is quite a bit more than it seems at
first glance.
Al
Just to get back on the rails...
Does anybody know why you cannot perfectly balance any 90 degree V
engine (v2, v4, v6) with crankshaft weights alone as is done with the
crossplane v8? What is so special about the crossplane v8? Thanks.
Tegger
2008-11-27 12:45:29 UTC
Permalink
Post by w***@yahoo.com
Just to get back on the rails...
Does anybody know why you cannot perfectly balance any 90 degree V
engine (v2, v4, v6) with crankshaft weights alone as is done with the
crossplane v8? What is so special about the crossplane v8? Thanks.
http://en.wikipedia.org/wiki/V6

The problem is a phenomenon called "primary couple", which as I understand
it, results when the center of the reciprocating mass hops up and down (or
side to side) as the crankshaft rotates.

A 90deg crossplane V8 has no primary couple, since the center of
reciprocating mass does not shift during crankshaft rotation.

In addition, I believe a V2 cannot have evenly balanced firing impulses.
(Harley Davidson: pah-PAH-pah-PAH-pah-PAH...)
--
Tegger
HLS
2008-11-27 13:59:55 UTC
Permalink
Post by Tegger
In addition, I believe a V2 cannot have evenly balanced firing impulses.
(Harley Davidson: pah-PAH-pah-PAH-pah-PAH...)
--
Tegger
OT, but did the old Triumph vertical twin have both pistons on the same
cycle?
Steve
2008-11-27 17:15:55 UTC
Permalink
Post by HLS
Post by Tegger
In addition, I believe a V2 cannot have evenly balanced firing impulses.
(Harley Davidson: pah-PAH-pah-PAH-pah-PAH...)
--
Tegger
OT, but did the old Triumph vertical twin have both pistons on the same
cycle?
Every 4-stroke vertical twin that I know of did. I'm not familiar with
the Triumph, but John Deere "johnny poppers" did. :-)
Steve
2008-11-27 17:14:37 UTC
Permalink
Post by w***@yahoo.com
Just to get back on the rails...
Does anybody know why you cannot perfectly balance any 90 degree V
engine (v2, v4, v6) with crankshaft weights alone as is done with the
crossplane v8? What is so special about the crossplane v8? Thanks.
For the umpteenth time... NOTHING is special about a 90-degree crank v8.

90-degree v6 engines are the ones that are "special" because they're
operating at the wrong bank angle. To get semi-even firing, you have to
give up some imbalance which is then corrected with balance shafts.
E Frank Ball III
2008-12-03 01:11:17 UTC
Permalink
Post by Steve
Post by w***@yahoo.com
Just to get back on the rails...
Does anybody know why you cannot perfectly balance any 90 degree V
engine (v2, v4, v6) with crankshaft weights alone as is done with the
crossplane v8? What is so special about the crossplane v8? Thanks.
For the umpteenth time... NOTHING is special about a 90-degree crank v8.
90-degree v6 engines are the ones that are "special" because they're
operating at the wrong bank angle. To get semi-even firing, you have to
give up some imbalance which is then corrected with balance shafts.
So why is even firing so important in the car world? Honda makes V4
motorcycle engines that are 90 deg Vs. It's like two v-twins on one
crank. It balances fine, but it doesn't have an even firing order.
V6s could be done the same way.
--
E Frank Ball ***@sonic.net
Steve
2008-12-03 17:16:48 UTC
Permalink
Post by E Frank Ball III
Post by Steve
Post by w***@yahoo.com
Just to get back on the rails...
Does anybody know why you cannot perfectly balance any 90 degree V
engine (v2, v4, v6) with crankshaft weights alone as is done with the
crossplane v8? What is so special about the crossplane v8? Thanks.
For the umpteenth time... NOTHING is special about a 90-degree crank v8.
90-degree v6 engines are the ones that are "special" because they're
operating at the wrong bank angle. To get semi-even firing, you have to
give up some imbalance which is then corrected with balance shafts.
So why is even firing so important in the car world? Honda makes V4
motorcycle engines that are 90 deg Vs. It's like two v-twins on one
crank. It balances fine, but it doesn't have an even firing order.
V6s could be done the same way.
Because consumers don't want a car that shakes like a Harley!

Actually, there are some very SUCCESSFUL odd-firing engines out there.
The Viper V10, for example, has a slight odd-fire because its a v10
built on a 90-degree bank angle. There are degrees of odd-firingness,
for lack of a better word. The v10 doesn't have a very large difference
in crankshaft rotation between the "close" cylinder pairs and the "far"
pairs. You can't even really feel it, although you can hear the dual
tones in the exhaust note. An odd-firing 90-degree v6 with a 3-throw
crank, on the other hand, has a very large and noticeable difference
between the close and far pairs, so that the engine seems very rough.
The manufacturers splay the crankpins and reduce the difference to
something manageable. They're still slightly odd-firing, but not so
extreme as a true 3-throw crankshaft would be.
Steve W.
2008-12-03 18:22:22 UTC
Permalink
Post by Steve
Post by E Frank Ball III
Post by Steve
Post by w***@yahoo.com
Just to get back on the rails...
Does anybody know why you cannot perfectly balance any 90 degree V
engine (v2, v4, v6) with crankshaft weights alone as is done with the
crossplane v8? What is so special about the crossplane v8? Thanks.
For the umpteenth time... NOTHING is special about a 90-degree crank v8.
90-degree v6 engines are the ones that are "special" because they're
operating at the wrong bank angle. To get semi-even firing, you have
to give up some imbalance which is then corrected with balance shafts.
So why is even firing so important in the car world? Honda makes V4
motorcycle engines that are 90 deg Vs. It's like two v-twins on one
crank. It balances fine, but it doesn't have an even firing order.
V6s could be done the same way.
Because consumers don't want a car that shakes like a Harley!
Actually, there are some very SUCCESSFUL odd-firing engines out there.
The Viper V10, for example, has a slight odd-fire because its a v10
built on a 90-degree bank angle. There are degrees of odd-firingness,
for lack of a better word. The v10 doesn't have a very large difference
in crankshaft rotation between the "close" cylinder pairs and the "far"
pairs. You can't even really feel it, although you can hear the dual
tones in the exhaust note. An odd-firing 90-degree v6 with a 3-throw
crank, on the other hand, has a very large and noticeable difference
between the close and far pairs, so that the engine seems very rough.
The manufacturers splay the crankpins and reduce the difference to
something manageable. They're still slightly odd-firing, but not so
extreme as a true 3-throw crankshaft would be.
Take a look at the early 231 Buick for an odd fire V6. Even the later
ones with split journals are not real smooth.
--
Steve W.
Steve
2008-12-04 17:10:48 UTC
Permalink
Post by Steve W.
Post by Steve
Because consumers don't want a car that shakes like a Harley!
Actually, there are some very SUCCESSFUL odd-firing engines out there.
The Viper V10, for example, has a slight odd-fire because its a v10
built on a 90-degree bank angle. There are degrees of odd-firingness,
for lack of a better word. The v10 doesn't have a very large
difference in crankshaft rotation between the "close" cylinder pairs
and the "far" pairs. You can't even really feel it, although you can
hear the dual tones in the exhaust note. An odd-firing 90-degree v6
with a 3-throw crank, on the other hand, has a very large and
noticeable difference between the close and far pairs, so that the
engine seems very rough. The manufacturers splay the crankpins and
reduce the difference to something manageable. They're still slightly
odd-firing, but not so extreme as a true 3-throw crankshaft would be.
Take a look at the early 231 Buick for an odd fire V6.
Exactly...
Post by Steve W.
Even the later
ones with split journals are not real smooth.
Smooth enough to be GM's most successful v6, if not one of the better
and probably the most successful v6 engines of all time.


No v6 is ever going to be a smooth as an inline six or v8, but since the
length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes down
to a choice of v6 or inline 4. Given that, the v6 handily wins the
smoothness contest.
Kevin
2008-12-04 18:53:37 UTC
Permalink
Post by Steve
Post by Steve W.
Post by Steve
Because consumers don't want a car that shakes like a Harley!
Actually, there are some very SUCCESSFUL odd-firing engines out there.
The Viper V10, for example, has a slight odd-fire because its a v10
built on a 90-degree bank angle. There are degrees of odd-
firingness,
Post by Steve
Post by Steve W.
Post by Steve
for lack of a better word. The v10 doesn't have a very large
difference in crankshaft rotation between the "close" cylinder pairs
and the "far" pairs. You can't even really feel it, although you can
hear the dual tones in the exhaust note. An odd-firing 90-degree v6
with a 3-throw crank, on the other hand, has a very large and
noticeable difference between the close and far pairs, so that the
engine seems very rough. The manufacturers splay the crankpins and
reduce the difference to something manageable. They're still
slightly
Post by Steve
Post by Steve W.
Post by Steve
odd-firing, but not so extreme as a true 3-throw crankshaft would be.
Take a look at the early 231 Buick for an odd fire V6.
Exactly...
Post by Steve W.
Even the later
ones with split journals are not real smooth.
Smooth enough to be GM's most successful v6, if not one of the better
and probably the most successful v6 engines of all time.
No v6 is ever going to be a smooth as an inline six or v8, but since the
length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes down
to a choice of v6 or inline 4. Given that, the v6 handily wins the
smoothness contest.
the early alumun buick v6 was a 60 degree v and just as smooth as any
v8, only the 90 degree v is odd fire. KB
--
THUNDERSNAKE #9

Protect your rights or "Lose" them
The 2nd Admendment guarantees the others
Steve
2008-12-04 18:58:38 UTC
Permalink
Post by Kevin
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since
the
Post by Steve
length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes
down
Post by Steve
to a choice of v6 or inline 4. Given that, the v6 handily wins the
smoothness contest.
the early alumun buick v6 was a 60 degree v
So are many current car v6 engines, but not all the vibration comes from
odd-firing.
Post by Kevin
and just as smooth as any
v8, only the 90 degree v is odd fire. KB
Not true. All v6s have a slight higher-order vibration that inline sixes
and 90-degree crank v8s don't have. But it is less noticeable than the
2nd-order "bounce" that inline 4s have without balance shafts. You have
to almost go feeling for it to notice it but it is there.
ben91932
2008-12-04 19:11:20 UTC
Permalink
Post by Steve
Post by Steve W.
Take a look at the early 231 Buick for an odd fire V6.
Exactly...
Post by Steve W.
Even the later
ones with split journals are not real smooth.
Ibeg to differ.
When GM split the journals 43degrees (IIRC) they became way smoother,
and when they finally got EFI they got silky smooth.
ray
2008-12-15 04:55:18 UTC
Permalink
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since the
length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes down
to a choice of v6 or inline 4. Given that, the v6 handily wins the
smoothness contest.
I wonder what a 2.5L V8 would sound like. Would it still sound like a V8?

Ray
Bret
2008-12-15 05:02:51 UTC
Permalink
Post by ray
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since the
length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes down
to a choice of v6 or inline 4. Given that, the v6 handily wins the
smoothness contest.
I wonder what a 2.5L V8 would sound like. Would it still sound like a V8?
Ray


I reckon it would :)
ray
2008-12-15 15:47:43 UTC
Permalink
Post by Bret
Post by ray
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since the
length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes down
to a choice of v6 or inline 4. Given that, the v6 handily wins the
smoothness contest.
I wonder what a 2.5L V8 would sound like. Would it still sound like a V8?
Ray
http://youtu.be/R1Ygf83DwlA
I reckon it would :)
Neat. I'm assuming that's like a 1/4 scale or 1/8 scale RC dragster
motor? Now, if only Pontiac made a G5 with rwd and a 3L V8....
bobj
2008-12-15 20:19:29 UTC
Permalink
Post by ray
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since
the length of an inline six is incompatible with most modern small car
designs and a v8 is too inefficient when made that small, it comes
down to a choice of v6 or inline 4. Given that, the v6 handily wins
the smoothness contest.
I wonder what a 2.5L V8 would sound like. Would it still sound like a V8?
Ray
a 2.5 V-8........ methinks a Daimler-SP250 has one that
size. It uses the old 60's aluminum Buick V8 that GM sold
them. Sounds pretty good too. The sound produced by any
engine is directly related to some ratio having to do with
the connecting rod length and the engine stroke.
bobj
2008-12-15 20:23:59 UTC
Permalink
Post by ray
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since
the length of an inline six is incompatible with most modern small
car designs and a v8 is too inefficient when made that small, it
comes down to a choice of v6 or inline 4. Given that, the v6 handily
wins the smoothness contest.
I wonder what a 2.5L V8 would sound like. Would it still sound like a V8?
Ray
a 2.5 V-8........ methinks a Daimler-SP250 has one that size. It uses
the old 60's aluminum Buick V8 that GM sold them. Sounds pretty good
too. The sound produced by any engine is directly related to some
ratio having to do with the connecting rod length and the engine stroke.
.....gotta take that back about the GM engine, but a few
British models did use it... the Daimler had it's own design ..
Steve
2008-12-15 22:37:15 UTC
Permalink
.....gotta take that back about the GM engine, but a few British models
did use it... the Daimler had it's own design ..
I'm not much of a Brit-car guru, but I was thinking that the Daimler v8
was a hemi-head engine with throguh-the-valvecover plug tubes similar to
a Chrysler hemi, unlike the Buick/Rover v8 that showed up in various
Triumphs and Range Rovers over the years.
Steve
2008-12-15 22:34:53 UTC
Permalink
Post by ray
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since
the length of an inline six is incompatible with most modern small
car designs and a v8 is too inefficient when made that small, it
comes down to a choice of v6 or inline 4. Given that, the v6 handily
wins the smoothness contest.
I wonder what a 2.5L V8 would sound like. Would it still sound like a V8?
Ray
a 2.5 V-8........ methinks a Daimler-SP250 has one that size. It uses
the old 60's aluminum Buick V8 that GM sold them. Sounds pretty good
too. The sound produced by any engine is directly related to some
ratio having to do with the connecting rod length and the engine stroke.
Well.... that, and cam timing, lobe-center separation, ramp rate,
intake/exhuast event timing, ignition timing, firing order, exhaust
valve configuration, intake plenum volume, intake/exhaust port
size/shape, exhaust manifolding, downstream exhaust plumbing.....

In the grand scheme of things, rod-ratio really is a fairly minor
contributor to engine sound.

What truly amazes me is that with all these variables, all 90-degree
crank v8s still manage to have an identifiable sound that says "I'm a
90-degree crank v8."
news
2008-12-16 00:35:37 UTC
Permalink
Post by Steve
What truly amazes me is that with all these variables, all 90-degree
crank v8s still manage to have an identifiable sound that says "I'm a
90-degree crank v8."
And I know I'm not alone when I say "and it's a glorious sound."

Seriously, I'm all for high tech... but what is it about the sound of a
V8 that just sounds so pleasing?

:)
N8N
2009-01-08 17:35:27 UTC
Permalink
Post by Steve
Post by Steve
No v6 is ever going to be a smooth as an inline six or v8, but since
the length of an inline six is incompatible with most modern small
car designs and a v8 is too inefficient when made that small, it
comes down to a choice of v6 or inline 4. Given that, the v6 handily
wins the smoothness contest.
I wonder what a 2.5L V8 would sound like.  Would it still sound like a
V8?
Ray
a 2.5 V-8........  methinks a Daimler-SP250 has one that size.  It uses
the old 60's aluminum Buick V8 that GM sold them. Sounds pretty good
too.   The sound produced by any engine is directly related to some
ratio having to do with the connecting rod length and the engine stroke.
Well.... that, and cam timing, lobe-center separation, ramp rate,
intake/exhuast event timing, ignition timing, firing order, exhaust
valve configuration, intake plenum volume, intake/exhaust port
size/shape, exhaust manifolding, downstream exhaust plumbing.....
In the grand scheme of things, rod-ratio really is a fairly minor
contributor to engine sound.
What truly amazes me is that with all these variables, all 90-degree
crank v8s still manage to have an identifiable sound that says "I'm a
90-degree crank v8."
*unless* it has an even-firing exhaust (e.g. Ford GT-40)

nate
ben91932
2009-01-09 15:09:45 UTC
Permalink
*unless* it has an even-firing exhaust (e.g. Ford GT-40)
nate
Any chance you know of a website with a pic of a GT40 crank?
I'd like to see it.
Thanks,
Ben
Steve
2009-01-13 15:54:53 UTC
Permalink
Post by N8N
*unless* it has an even-firing exhaust (e.g. Ford GT-40)
nate
Any chance you know of a website with a pic of a GT40 crank?
I'd like to see it.
Thanks,
Ben
IIRC the GT40 crank is just an ordinary 90-degree crank. What it has
different is a set of exhaust plumbing that criss-crosses a pair of
cylinders so that each of the dual exhaust tubes is even firing, unlike
any configuration where you just take the 4 left cylinders for one pipe,
and the 4 right cylinders for the other pipe from a 90-degree crank v8.

"Flat-crank" or "180-degree crank" v8s (think late 90s IROC or CART, I
forget which) fire that way naturally, but have worse high-order
vibration than an inline 4, because they are TWO inline 4s set at an
angle. Thats why flat-crank v8s are never used for street cars.

Steve
2008-11-27 17:12:23 UTC
Permalink
Post by Anumber1
In a "just for thought" moment...
I think one of the balanced designs ever were the Fairbanks/Morse
opposed piston diesels of the late 1940's to be incredibly well
balanced. Unfortunately, the design did not lend itself to "easy" repair
of the lower cylinders and proved to be quite a maintenance hassle.
They were very clever alright. No valves at all, one bank of pistons
uncovered the inlet ports and the other bank of pistons uncovered the
exhaust ports at the appropriate times. Therefore, no crankshaft, no
rockers, no valves. But you're wrong about the way they were balanced-
each crankshaft and its pistons was balanced independently and did NOT
interact with the balance of the opposing pistons and crank at all.
That's because the cranks were timed slightly out of phase- in F-M lore
its called "lower crank lead." The lower crank's pistons reached and
passed TDC slightly before the opposing upper crank pistons did, so that
at BDC the exhaust port (uncovered by the lower pistons) would be opened
before the intake port to allow initial de-pressurization of the
cylinder, and the intake port (uncovered by the upper pistons) would be
covered slightly after the exhaust port allowing the blower to
pre-pressurize the cylinder. IF the balance had been dependent on one
crank balancing the other, it wouldn't have worked because there could
have been no lower-crank-lead.
Steve
2008-11-25 17:42:43 UTC
Permalink
Post by w***@yahoo.com
Hi - I'm trying figure out if crankshaft counterweights can be
effectively used on other engines besides 90 degree v8s with
crossplane cranks.
The question doesn't compute. ALL inline engines, with the exception of
extremely low-speed diesels, have counterweights. Look at a picture of
an inline-six crank, for example a Chrysler slant-six:

Loading Image...


An AMC (Jeep) 258 crank:

Loading Image...


How about a Rolls Merlin V12:

Loading Image...

How about one of the largest gasoline piston engines ever built, a 4-row
radial:




About the only type of medium-speed or high-speed engine that doesn't
have counterweights is a horizontally-opposed engine like a Porsche, VW
or Subaru auto engine, or Lycoming or Continental airplane engine:

Loading Image...

And even then there are small counterweights to account for the fact
that each pair of opposed pistons is very slightly offset from each
other and would make the engine rotate back and forth in the plane of
the cylinders without some counterbalancing.
Post by w***@yahoo.com
Now I know I'm missing something, otherwise this would have been done
already. What am I missing?
That the vast majority of engines other than opposed types and low-speed
(sub-500 RPM max speed) types DO use crank counterweights.
ben91932
2009-01-08 03:04:59 UTC
Permalink
Post by Steve
About the only type of medium-speed or high-speed engine that doesn't
have counterweights is a horizontally-opposed engine like a Porsche, VW
Hello,
Take another look at
the crank in the link below.
Post by Steve
http://www.sacskyranch.com/lyc_crank_gear.jpg
Notice the 2 crank throws outside of the outboard main journals?
Those hammerhead looking lumps are balance weight.
*Every* crank on *every* modern engine has some form of counter
balance,
even if its just Mallory metal pressed into the rod journal.
Your best bet for complete understanding of balance dynamics
is to find your local machine shopor spped shop that does balancing,
take the guy a 6pack
and ask him to let you look over his shoulder while he's doing one
and have him 'splain it to you. I did that with the guy who does the
cranks
on all my race cars (I do all the pistons and rods before-hand to save
a few bucks).
I would also suggest posing this question on the forums at eng-
tips.com
There is a wealth of info there.
HTH,
Ben
jim <"sjedgingN0sp"@
2009-01-09 15:32:58 UTC
Permalink
Post by ben91932
Post by Steve
About the only type of medium-speed or high-speed engine that doesn't
have counterweights is a horizontally-opposed engine like a Porsche, VW
Hello,
Take another look at
the crank in the link below.
Post by Steve
http://www.sacskyranch.com/lyc_crank_gear.jpg
Notice the 2 crank throws outside of the outboard main journals?
Those hammerhead looking lumps are balance weight.
Actually, no that is probably incorrect. Those bosses are probably what
foundries call "locators" There are actually 3 that I see in that picture
and their purpose is to provide a way to reference and coordinate the
orientation of the crankshaft for first machining operation, quality control
fixturing and tooling design at the foundry.
Post by ben91932
*Every* crank on *every* modern engine has some form of counter
balance,
Yes probably true, but since all this can be modeled in computers nowadays
the weight distribution can be fairly easily incorporated into the whole
design and as a result what is added or subtracted for weighting may not be
so obvious. The locators play an important role because they enable each
part to be fixtured and machined in a repeatable way. Which means the weight
distribution will be pretty close to the same.

-jim
Post by ben91932
even if its just Mallory metal pressed into the rod journal.
Your best bet for complete understanding of balance dynamics
is to find your local machine shopor spped shop that does balancing,
take the guy a 6pack
and ask him to let you look over his shoulder while he's doing one
and have him 'splain it to you. I did that with the guy who does the
cranks
on all my race cars (I do all the pistons and rods before-hand to save
a few bucks).
I would also suggest posing this question on the forums at eng-
tips.com
There is a wealth of info there.
HTH,
Ben
Steve
2009-01-13 15:50:29 UTC
Permalink
Post by jim <"sjedgingN0sp"@
Post by ben91932
Post by Steve
About the only type of medium-speed or high-speed engine that doesn't
have counterweights is a horizontally-opposed engine like a Porsche, VW
Hello,
Take another look at
the crank in the link below.
Post by Steve
http://www.sacskyranch.com/lyc_crank_gear.jpg
Notice the 2 crank throws outside of the outboard main journals?
Those hammerhead looking lumps are balance weight.
Actually, no that is probably incorrect. Those bosses are probably what
foundries call "locators" There are actually 3 that I see in that picture
and their purpose is to provide a way to reference and coordinate the
orientation of the crankshaft for first machining operation, quality control
fixturing and tooling design at the foundry.
Opposed-piston engines do have vestigial balance weights on the outboard
ends. It compensates for the fact that the pistons aren't actually
DIRECTLY opposite each other, but are offset by one throw distance.
Compared to the weights on other crankshafts, they're practically
nonexistent. Without them the engine would have a rotational vibration
making it want to twist back and forth around an axis perpendicular to
the plane containing the cylinders.

Ben91932 obviously hadn't followed the whole thread through or he would
have seen that we'd been through that already.
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