Counterweights vs Balancing Heads Up

[edmondclinton]

Now, regardless of Ford's brag and balancing statements, etc. in my post above, anybody with any experience knows that the A crank, as Henry made it, has a strong tendency to whip, both at the center and at the ends.

If you study the distribution of weight masses on an original A shaft, you will quickly see that although the thing is basically in balance statically, it is far out of balance when in motion. The centrifugal forces developed by the unbalanced weights of the circular throws tend to pull the center of the shaft in one direction and at the same time pull the ends of the shaft in the opposite direction. Also, the bolting on of the connecting rods compound the imbalance.

The result of this is vibration and bearing wear. Before I knew better I used to wonder why the center main always seemed to be worn out.

Counterweights will minimize this whipping effect and reduce vibration. Try it and you'll see.

[johnneilson]

You can "balance" a inline 4 motor to only a certain point.
The most of the "felt/perceived" in-balance is the non-symmetrical acceleration of the pistons at top and bottom of stroke. Long stroke and big piston is largest contributor along with speed of operation.

J

[edmondclinton]

Originally Posted by Bob Bidonde

However, that heavy flywheel is mechanically inefficient because:
>It requires considerable torque to accelerated / decelerate it;
>It places high stresses in the rear main bearing;
>It increases the twisting stress (torsional shear stress) in the crankshaft;
>It makes the rear engine mounts the pivot in a seesaw which lead to the inefficient design of the front engine mount.

Not completely inefficient.

The heavier the flywheel the smoother the idle, the easier it is to move the car from a dead stop and any slight throttle changes are smoother. Also, the energy of a heavier flywheel, once in motion, was considered back in the day to be a plus for moving the Model A through soft dirt, etc. while in lower gear at slow speed.

BUT .... once the heavy flywheel energy is used up, the engine has to provide more power to keep the extra weight spinning and the extra weight, as compared to a lighter flywheel, becomes an opposing force.

[BRENT in 10-uh-C]

Originally Posted by edmondclinton

For those who are interested, Ford's precision on the Model A was as follows:

Connecting rods balanced to within 2 grams. Total weight held to within 4 grams of limit.

Pistons were matched within 2 grams. Total weight held to within 4 grams of limit.

Piston assemblies matched in weight within a limit of 3.5 grams.

Piston pin and pin hole diameter held to within .0003 of an inch.

Crankshaft was balanced dynamically to within 4 grams.

Main and connecting rod bearings were held to .00025 of an inch of true roundness.

Crankshaft bearing alignment in the block was held to within .0005 of an inch of absolute true.

If you don't mind me asking, where are you getting these numbers above?

Maybe you have better resources than I, but quite honestly, my prints for A-6200-A rods, A-6110-BR & CR pistons, A-6325 Main Cap, etc. are showing different specs than what you are stating. Maybe you are saying some of this in a different manner however using the connecting rod as an example, I did not see anything regarding 4 grams. It simply shows that all rods must be 198 ± 1 gram on the wrist pin end, and 525 ± 1 gram on the babbitted end. I guess my thought is the maximum amount of possible difference is 2 grams (1 gram for each end). By you stating there could be a variation of 4 grams would indicate that a rod was out of specification.

You also mentioned the piston pin to hole clearance was three ten-thousandths, yet on the print it stated the ± was .9995 - 1.000. On my crankshaft print, it says "SHAFT MUST BE IN BALANCE DYNAMICALLY WITHIN .3 OUNCE INCH AT ANY ONE POINT OF REFERENCE". It also states on the print that it must be statically balanced within .3 ounce inch too. It speaks of axes (axis??) specs of the rod journal pins in relation to the main journal pins, and it speaks about runout of flanges, pilot holes, and crank gear shoulders, but nowhere that I can see on the print does it mention the word "grams". Where are you finding this? The same thing with the main cap. It gives a specification however it is much greater than what you have indicated.

TIA.

[mshmodela]

Likely True, and for smooth power: Wankel engine

Originally Posted by MikeK

No amount of crankshaft counterweighting or flywheel weight manipulating can eliminate the primary imbalance of an I-4 engine. The primary imbalance is caused by unequal forces and piston velocities between upstrokes and downstrokes. Only weights mounted on a separate counter rotating shaft can cancel most of this and a give real seat-of-the-pants improvement. The problem is exacerbated by the A engine design, with exceptionally long rods and a stroke exceeding the bore.

Counterweights serve only to reduce crank main bearing radial loading. Anyone who feels "seat of the pants" improvement from a counterweighted crank and/or change of flywheel momentum (a bit more complicated than 'weight') is only seeing an improvement compared to a less-than-factory rebuild.

There are definite engine life benefits to a counterweighted crank and sufficient dampened external rotational mass at both ends of the crank to reduce torsional harmonics, but you will not feel it compared to an engine that came off the line at the Rouge balanced to Henry's specs.

[Kohnke Rebabbitting]

Sponsored Links (Register now to hide all advertisements)

Originally Posted by edmondclinton

Now, regardless of Ford's brag and balancing statements, etc. in my post above, anybody with any experience knows that the A crank, as Henry made it, has a strong tendency to whip, both at the center and at the ends.

If you study the distribution of weight masses on an original A shaft, you will quickly see that although the thing is basically in balance statically, it is far out of balance when in motion. The centrifugal forces developed by the unbalanced weights of the circular throws tend to pull the center of the shaft in one direction and at the same time pull the ends of the shaft in the opposite direction. Also, the bolting on of the connecting rods compound the imbalance.

The result of this is vibration and bearing wear. Before I knew better I used to wonder why the center main always seemed to be worn out.

Counterweights will minimize this whipping effect and reduce vibration. Try it and you'll see.

The weight of the flywheel is what takes its toll on the center main, as the crank runs bowed in the middle. The heaver the flywheel, the heavier and more pressure the bow.

Model T cranks are the opposite, the flywheel is supported on both sides of it with 2 bearings, rear main and the ball cap, so the front and center don't wear near as much an the rear main which carries most of the weight because it is closer.

Model T cranks will may be wore 3 to 6 thousandths on the front and middle, where the rear can be wore .030 thousandths.

Where as a Model A will be wore .003 to .006 thousandths on the front and rear main, and the middle wore .020.

Herm.

[edmondclinton]

Originally Posted by BRENT in 10-uh-C

If you don't mind me asking, where are you getting these numbers above?

Maybe you have better resources than I, but quite honestly, my prints for A-6200-A rods, A-6110-BR & CR pistons, A-6325 Main Cap, etc. are showing different specs than what you are stating. Maybe you are saying some of this in a different manner however using the connecting rod as an example, I did not see anything regarding 4 grams. It simply shows that all rods must be 198 ± 1 gram on the wrist pin end, and 525 ± 1 gram on the babbitted end. I guess my thought is the maximum amount of possible difference is 2 grams (1 gram for each end). By you stating there could be a variation of 4 grams would indicate that a rod was out of specification.

You also mentioned the piston pin to hole clearance was three ten-thousandths, yet on the print it stated the ± was .9995 - 1.000. On my crankshaft print, it says "SHAFT MUST BE IN BALANCE DYNAMICALLY WITHIN .3 OUNCE INCH AT ANY ONE POINT OF REFERENCE". It also states on the print that it must be statically balanced within .3 ounce inch too. It speaks of axes (axis??) specs of the rod journal pins in relation to the main journal pins, and it speaks about runout of flanges, pilot holes, and crank gear shoulders, but nowhere that I can see on the print does it mention the word "grams". Where are you finding this? The same thing with the main cap. It gives a specification however it is much greater than what you have indicated.

TIA.

Ford Dealer and Service Field

The Acme of Precision

[Kohnke Rebabbitting]

You also mentioned the piston pin to hole clearance was three ten-thousandths, yet on the print it stated the ± was .9995 - 1.000. "END QUOTE"

That is not right as 1.000 is an inch, don't ya think it would make some kind of a little noise!

I think that is your wrist pin O.D.




I know that wrist pin clearance should be .0003, to .0005, no more, and or no less,


and .001-00 would also be already wore out.

[edmondclinton]

Originally Posted by Kohnke Rebabbitting

The weight of the flywheel is what takes its toll on the center main, as the crank runs bowed in the middle. The heaver the flywheel, the heavier and more pressure the bow.

Herm.

Sorry, I don't completely agree.

[edmondclinton]

Originally Posted by Kohnke Rebabbitting

You also mentioned the piston pin to hole clearance was three ten-thousandths, yet on the print it stated the ± was .9995 - 1.000. "END QUOTE"

That is not right as 1.000 is an inch, don't ya think it would make some kind of a little noise!

I think that is your wrist pin O.D.




I know that wrist pin clearance should be .0003, to .0005, no more, and or no less,


and .001-00 would also be already wore out.

Yes, the hole diameter was held to within .0003 clearance over the pin O.D.

[tbirdtbird]

Except for Pete, the consensus has been that counterweights are beneficial, with partial or full endorsement.
Put another way, if they were not beneficial, why would all modern day cranks (since the '40s) have them?

[Pete]

Statement by tbirdtbird.

"If A modern day flywheel (say 25 lbs) were used on a stock A crank the engine would vibrate itself to death in short order and your teeth would jar out of your head in less than a mile."

Since you seem to be having trouble understanding basic engine design, I will give you some examples of what has been going on in the past and present.
Back in the 30's when model A and B engines were popular in sprint cars (called big cars in those days) they ran no flywheel at all. Most real race cars of today (not vintage class) run no flywheel. The crank is connected direct to the u-joint.
The race engines of the 30's did not vibrate any more than a stock model A right out of the factory door.
I build vintage circle track engines and the ones that get flywheels use an 11 lb 350
Chev V8 flywheel. They sure don't shake your teeth out and they turn 6000 rpm.

As far as getting rid of the felt vibration in an A/B engine, as others have said, it can't be done without redesigning the engine. You can not get enough counterweight on the crank. I took a BB crank one time and cross drilled the weights and put heavy metal in the holes. It did reduce the vibration slightly but
the engine was quite sluggish coming off the corners due to the added weight on the crank besides the BB crank being much heavier in the first place.

[tbirdtbird]

Bill Stipe, throw those cranks away!!!

[Kohnke Rebabbitting]

Originally Posted by edmondclinton

Yes, the hole diameter was held to within .0003 clearance over the pin O.D. diameter.

And your point would be , ED.

[Ron W]

I hope peoples panties aren't getting in a pucker over what tbirdtbird was trying to explain. Yes, engines should be balanced as well as possible. Beyond balancing, the rotational pulses are what people perceive as "imbalance". They try to twist the motor. I have one of the smoothest Ford 4 cyl engines that I have ever seen. It is not in my Model A but I have thought about putting it in one. It has a counter weighted crank. It has a separate counter balance shaft that turns opposite the crank. The cylinders form a "V", 2 on each side. It was made by Ford in Europe and used in '60's Saabs. Ron W

[edmondclinton]

Originally Posted by Kohnke Rebabbitting

And your point would be , ED.

There is no point. I was agreeing with your statement about wrist pin clearance.