Crankshaft Counterbalance Weight

Bob Bidonde

Bob Bidonde

Well-known member
I need your help again. It seems I have a lot of questions these days. Actually, I am working on presentations for my local club, so questions arise I never thought of before.
At this time I am building a presentation about engine vibrations which leads to this question. What is the weight of one crankshaft counterbalance weight before it goes onto a crankshaft?
 
Early '28, so-called 'beaver-tail' cranks weigh 27 lbs.
Later A's weigh 29 lbs.
B cranks, 39 lbs.
C cranks, 46 lbs.
BB cranks, 58 lbs. (pressed-on, 1" wide weights. So called because these were added by authorized Ford rebuilders when a 'B' engine was rebuilt, mostly on 'B' trucks.
I may have some weights I planned on putting on a 'B' crank, I'll look for them.

A & B engines have naturally occuring vibration points, at about 800-900, 1600, and 2300 (this from my menory) They are heard more than felt, in most engines they aren't noticeable, and usually when being driven, not sitting in your driveway.
 
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Interesting inquiry, I found old picture of B-B counterweight drawing some years ago.
I then modeled up in solidworks, from a pretty bad sketch.

I come up with mass of #4.87 per counterweight.

As an interesting side note, the Miller racing engines found that you could not get enough counter weight to balance out the harmonics. If you look at pics of them, the counterweight is full radius and 180 degrees opposite the rod journal.

John
 
I have s set of counterweights from Berts. Bolt on then weld the ends. Set of 4. Each one weighs 3.1 lbs total weight of 12.4 lbs. They are the samee thickness as the counters on the crankshft - 5/8" thick.



also. crankshft turned 10/10 under weighs in at 24.8 with no counterweights. Second crankshaft also turned 10/10 under with the above weights added weighs in at 37 lbs.
 
What exactly are the counterbalance weights for. What effect would it have on my engine if it was not counter balanced.
Gerry Birch Bay WA.
 
daren007 said:
Is it possible to “turn” a crankshaft as opposed to grinding.
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Yes. It is possible to "turn" a crank in a lathe by offset mounting it on 2 face plates. We made a single plane crank for a cut in half Chev V8 this way once.
 
From what I have heard, what ever you do to put counterweights on an A crank, you won't have the optimum. Right now, I don't remember the name of the guy who attaches shrink on weights to the crank, then puts more weight on the side of those. I think that setup would be heavier than the others and closer to ideal.
Clearly, shrink on weights will weigh more than the weld on ones because they go all the way around the crank flange without adding any more counterweight effect. I don't think we have enough information to properly answer this question.
 
Synchro909 said:
From what I have heard, what ever you do to put counterweights on an A crank, you won't have the optimum. Right now, I don't remember the name of the guy who attaches shrink on weights to the crank, then puts more weight on the side of those. I think that setup would be heavier than the others and closer to ideal.
Clearly, shrink on weights will weigh more than the weld on ones because they go all the way around the crank flange without adding any more counterweight effect. I don't think we have enough information to properly answer this question.
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Using steel weights, about the maximum you can cram into the space available is 65%. By lightening the reciprocating assembly to a minimum safe value and using tungsten or depleted uranium for weights you could probably get very close to optimum. HOWEVER, I can tell you from first hand experience, an engine built this way is a horrible slug on a circle track.
It would do well in parades.
 
Pete said:
Using steel weights, about the maximum you can cram into the space available is 65%. By lightening the reciprocating assembly to a minimum safe value and using tungsten or depleted uranium for weights you could probably get very close to optimum. HOWEVER, I can tell you from first hand experience, an engine built this way is a horrible slug on a circle track.
It would do well in parades.
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Who wouldn't lighten the flywheel to compensate for the extra weight on the crank?
 
Synchro909 said:
Who wouldn't lighten the flywheel to compensate for the extra weight on the crank?
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Assuming you have used enough depleted uranium to balance the CRANK ASSEMBLY completely, the flywheel/clutch and damper weight has nothing to do with crank balance.

A heavy total weight, crank assembly limits the performance of any car not only by total weight added to the car but MOSTLY because of poor spool up.
This is usualy of little concern in a vintage street machine though.
 
Thanks Ken Parker. This is exactly what I asked for:
I have s set of counterweights from Berts. Bolt on then weld the ends. Set of 4. Each one weighs 3.1 lbs total weight of 12.4 lbs. They are the samee thickness as the counters on the crankshft - 5/8" thick.

Also crankshft turned 10/10 under weighs in at 24.8 with no counterweights. Second crankshaft also turned 10/10 under with the above weights added weighs in at 37 lbs.
 
Gerry Allen, counterweights increase the life of the crank & bearings. You will feel little or no increase in smoothness while driving.
 
What kind of lathe would you need to “Turn” crankshaft journals. How accurate finish can be obtained. Does anyone have more info and pictures?
 
daren007 said:
What kind of lathe would you need to “Turn” crankshaft journals. How accurate finish can be obtained. Does anyone have more info and pictures?
Click to expand...

This is kind of a loaded question IMO. A crankshaft could be "roughed-in" using a lathe however the only advantage is how quickly it can be done. The advantage to using a crankshaft grinder is, I can hold a tolerance to less than a couple of tenths however this comes at a price of much slower removal of journal material.

I have a Storm Vulcan 15 crankshaft grinder, -and my biggest lathe is a Howa 16" x 59". Both machines weigh around 4,500 pounds, yet the crank grinder is a much more rigid machine comparing the two. When trying to achieve a quality finish, rigidity is a must. So my point is you would need a very robust lathe to achieve a finish you could be happy with. Using a tool-post grinder on that lathe would be a plus.
 
Would this one be rigid enough? It is a 42 inch throw facing and boring lathe weighing 10.5 tons without the face plate shown. There is no tail stock on this type but another face plate or a precision steady can be mounted on the rear.
My son and I are just fettling and setting it up in our collection.
I am just joking because I have no intention of machining a crankshaft in it.
I have trued up several Model A rear flanges in another of our lathes, after straightening the cranks in a press.
A crank grinder is something missing in our collection of machine tools.
 

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