Counterweights vs Balancing Heads Up

[tbirdtbird]

Looking closely at postings and blogs it has become very clear that there is a lot of confusion/misunderstanding of what these two terms really mean.

[mshmodela]

Tbird, great post, thank you.

[pgerhardt]

My 29 tudor has a 1936 diamond block engine. Since counterbalanced cranks were introduced in 1932, would my 1936 diamond block have a counterbalanced crank?

[Rowdy]

I doubt it. None of the diamond block A engines have had a counterbalanced crank in them. Other than the B cranks that had larger journals, Ford did not make a counterbalanced cranks cor this era of four cyl's. Rod

[redmodelt]

Even a Model T crank can be balanced. Simply means that the weight on both side of center are the same. A good balance job includes the flywheel, crank, presure plate and pulley for people not using counter balanced crank. Also rods and pistons within a few grams of each other. While this would not get rid of vibration like a counter weighted crank might, it should help a lot.

[Pete]

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Originally Posted by tbirdtbird

Looking closely at postings and blogs it has become very clear that there is a lot of confusion/misunderstanding of what these two terms really mean.

Crankshaft counterweights are designed to offset the inertia effect of a relatively heavy piston and connecting rod moving in both a rotational and reciprocating (up-and-down) fashion at speed.
Thus the crankshaft is designed to rotate smoothly and it has counter weights positioned to counteract the thrusting forces caused during the running cycle.

A statement was made that a stock A crank (meaning with no counterweights) could be 'balanced better than Henry did in in 1928'. This is very misleading, since there are no counterweights present to offset the weight of the pistons and rods. 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.
So, Henry made the flywheel a massive 62 pounds. This reduced, but did not eliminate vibration. Anyone who has ever driven a stock A can attest to this.

The Model B started out the same way; ie crank with no counterweights. When the early (1932) Model BB trucks came in for overhaul Ford dealers added the so-called BB weights to the crank...they were shrunk on. I have not that long ago posted pix of just such a crank, in fact the pix show us shrinking the weights back onto the crank. However, by 1933-4 Henry realized that not using counterweighted cranks was just not gonna work anymore as cars evolved and greater demands were placed on them, so the later Model B cranks were indeed counterweighted. These cranks are the so-called "C" cranks.

I have included pix of a stock A crank side by side to a brand new Scat A crank. The red areas show clearly where metal is "missing" from the stock A crank. Study the pic carefully to realize where the extra metal (the counterweights) were added to the Scat crank. The Scat crank actually looks a lot like the "C" crank (of course the A and B journal sizes are different but that is not the point of this).

One solution to the original problems Henry left us with (and as a result of the lack of counterweights the bearings take a beating, the massively heavy flywheel causes the crank to whip around and eat up the center main, and also hammers against the thrust which is built into the rear main babbitt casting (another failure point unto itself), etc etc. is to add counterweights to the existing stock A cranks. Most all rebuilders have the capability to do this in house or farm it out; but nonetheless are able to offer this service for those discriminating customers who want it. I do not at this time have a pic of such a crank. If I find one I will add it. Maybe someone else out there has one they can take a pic of.

Another solution is to buy a fresh Scat crank which has the weights build into the forging (More pricey, tho)

A last option is to take a stock A crank and not only add the counterweights as above but to also add the extra weight off the side of the weights in the manner of the BB crank. This is IMO the best of all options since these motors are very very smooth running. Smoother=more longevity.

OK I just located some really nice pix Bill Stipe posted, and he shows the addition of the BB style weights
https://www.fordbarn.com/forum/showth...+counterweight

Miles is having just such a motor built (inserted of course) and will take delivery soon and we can't wait to get our hands on it.

The last comment I will make is one that has been made repeatedly on this forum.
If you are even remotely considering an engine option that is not stock, take the time to seek out another A owner who has that option and ride/drive the car so you can see for yourself what is going on. You won't be sorry. And the engine will still be running strong for your kids in 40 yrs.

After the second paragraph, most of the info is wrong or partially wrong.
I'm not going to elaborate on the details because all of the correct information on balancing automotive engines is covered by numerous articles all over the internet.

[tbirdtbird]

so give us your version
a lot of the info was lifted from the Scat and Eagle websites

[Pete]

"I'm not going to elaborate on the details because all of the correct information on balancing automotive engines is covered by numerous articles all over the internet."

[P.S.]

My 29 with a dead stock, never been apart motor is smoother and quieter than my 31 with a balanced, inserted, counterweighted crank touring rebuild. Admittedly, the rebuilt motor has more power. The motor that has never been apart runs fantastic. The rebuilt is strong and torquey, but will vibrate your glasses right off our face. That car is developing new rattles all the time.

[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.

[colin1928]

I have used a 12 lbs aluminium flywheel on a stock but well mechanically balanced
and still have all my teeth in my head
that is to say it had no more vibration then engines with a heavy flywheel
the counter weighed cranks that we commonly see are NOT counterbalanced cranks they have only a small % of the weight need to counted the throw weight
just do the math
the only ones that even come within a bulls roar are Dans
when added to a good mechanical balancing
Mikes is correct inline 4 have lots of problems with balancing
let us not mention thing such as the added weight of 3 of the 4 strokes in our 4 stroke engines and negative weight on the other stroke this effect increases as compression gets higher 1 reason a stock low comp engine is smoother or the effect of big ends plunging into a trough of oil at the bottom of the stroke
IMO if we want smoother and more power full engines we would be better off with a 2up 2down crank and a harmonic balancer

[inex01]

Great post and now I can better better understand why Henry used the heavy flywheel, guess I am very lucky because both my 31s have very little vibration, actually my Roadster is smooth as silk .

[Bob Bidonde]

The use of a heavy flywheel is an inexpensive way of damping the vibrations of the Model A engine. 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.

[Joe K]

IMO if we want smoother and more power full engines we would be better off with a 2up 2down crank and a harmonic balancer

Henry thought enough of that idea to experiment with an X8 configuration for the Model T.

Joe K

[J and M Machine]

A statement was made that a stock A crank (meaning with no counterweights) could be 'balanced better than Henry did in in 1928'. This is very misleading, since there are no counterweights present to offset the weight of the pistons and rods. 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.
So, Henry made the flywheel a massive 62 pounds. This reduced, but did not eliminate vibration. Anyone who has ever driven a stock A can attest to this.

This statement isn't entirely true. Due to the fact that: balancing machines have improved and we can now balance a rotating assembly better than henry did in 1928.
We are not working to Ford factory spec as they balanced everything to approximately 6 grams. We are now balancing parts to less than .2 tenths of a gram.

Balancing is one part the harmonics of the engine are another as "MikeK" pointed out.

We have balanced many engines and stock versus counterweighted, naturally the counterweights do add to the dampening effect.

However for the customers who don't want to spend the extra money for the counterweighted cranks the engines run well since they are balanced.

If you look close at the two printout sheets you'll notice what the unbalance was for the crankshaft and the pressure plate/flywheel.
Flywheel started out a 71 grams.! Now it's balanced to .3 grams at 4000 rpm.
Same applies to the crankshaft now final balanced to under a tenth of a gram.

If the machine shop does a good job balancing the engine the vibration "Harmonic" is moved to a higher plane that the rpm's of the engine won't be able to reach.
Therefore the engine runs smooth for what it's designed to do.

http://www.jandm-machine.com/balancing.html

[sethkestenbaum]

While I lack the background to contribute anything of technical value, I do want to say I am enjoying the post and the back and forth. At a minimum, this is helping me figure out some of the right questions to ask and options to consider. Thanks all!

[Kohnke Rebabbitting]

Originally Posted by P.S.

My 29 with a dead stock, never been apart motor is smoother and quieter than my 31 with a balanced, inserted, counterweighted crank touring rebuild. Admittedly, the rebuilt motor has more power. The motor that has never been apart runs fantastic. The rebuilt is strong and torquey, but will vibrate your glasses right off our face. That car is developing new rattles all the time.

Mr. PC, there can be many things wrong with a rebuild, done or not done by a builder.

If it is as bad as you say, then something was over looked.

Herm.

[BRENT in 10-uh-C]

Revisiting this thread from awhile ago may be of some interest.....

https://www.fordbarn.com/forum/showthread.php?t=89197


.

[Kohnke Rebabbitting]

As far as the cranks go, all the motors I have bought or built in the 1932-34 engines. the crank styles were.

1. crank with no weights.

2. Cranks with weights, as part of the crank.

3. Crank with weights shrunk on like we made for 38 years.

In that order of manufactuer.

This is one of our A cranks, 5/8's wide. and no need for the wider part of the weight unless your hauling a load of corn in your truck.

We don't build these cranks now, as we don't have time.

One last thing, these cranks came out in almost perfect balance, before balancing.

Herm.

[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.