Balancing the pistons of the Model A Ford

[SSsssteamer]

A year ago I balanced my model A engine's pistons and my connecting rods as shown in the following video. I am totally amazed about how much smoother my '31 model A engine now runs after being balanced this way. I bought my scale at a garage sale for $2. See the how to video at: http://automoto101.com/piston-balanc...m_medium=Trust

My final weigh in was done with comparing the piston assemblies with each other.

[kenparker]

I did that with the engine that is now on the engine test run stand. It has countr balsnced crank, and lightened fly wheel and v8 PP. The crank and flywheel and clutch were balanced by pro with high dollar equipment. The rods and pistons were balanced by me just like the video above. Rods and pistons were balanced to within 1/4 gram. On the engine stand it is one smoooooooooooooooth running engine. Today project is to change th distributor from a stock dizzy to a FS electronic. Then we will see again how smooth it is. Final step will be to put a downdraft carb on it before install in 'le coupe.

Have not decided whether to use a Stromberg 97 or get on of those Webers. ken

[Kevin in NJ]

It nice to hear people having great results from careful work!!

Imagine what a factory engine was like.

There the rods would be +-1g at each end. When matched with pistons the whole units would be within 4 grams of each other in an engine. Coupled with tightly balanced crank and a well centered and balanced flywheel.

I mention this because I think it is pretty rare to get all the parts to the level the factory would have had the balance and machining precision. The more I learn the more I find Ford, during production, maintained some pretty high standards for precision work in high volume. It is difficult to get the same level of precision without some very special setups.

That being said, there are clearly people getting pretty darn close. The more we try the bettter we get.

[Colonel Biggs]

Where did you do the balancing on the connecting rods?

Gordon
Houston

[BillLee/Chandler, TX]

A couple of questions regarding what I saw on the video:

1. When is "close" == "good enough"? The video started out with a max variance in pistons of 1.2 gms and .2 gms for the wrist pins. For that example, we're talking about .3% Seems that a gram difference for a 330 gm piston should be "good enough".

2. Why do the pistons and wrist pins separately? Since the video is very specific about not mixing them up, it seems to me that since they are a unit when delivered and will always be a unit forever, that the total weight of the piston and wrist pin needs to be balanced, not necessarily each individual piece.

Not trying to contradict what has been said, just trying to understand.

[kenparker]

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Bill, maybe we need to do some piston weighing tomorrow. juz fer fun. If close enough is good enough, but you have the equipment and are capable to get within 1/4 gram, why not do your best. Less than your very best is not good enough to me. ken

btw I weighed the pins separately just ot getthe measure/weight, then put them together and final weigh was with piston, pin and keepers.

Colonel, I will get pictures and be back tomorrow. ken

[H. L. Chauvin]

Hi Steamer,

Thanks, and in my opinion, if every professional mechanic and/or every shade tree mechanic, and/or every Model A owner in the past 60 years would have considered:

1. Carefully trying to obtain Model A mechanical precision in lieu of employing the very normal "good enough for a Model A" technology that existed back then; and,

2. Adhering strictly to proper Ford recommended Model A maintenance,

many of these tough Model A's that went to the junk yard would still be here among today.

Trying to achieve Model A mechanical precision & excellence, and generally trying to do it all right, always pays off in the long run not to constantly be wasting valuable time and money on constant Model A rebuilding and repairs.

[kenparker]

Said I would be back tomorrow. Well, my Falcons are winning and the game got boring, so out to the shop to take pictures.

Four pictures showing weighing the big end, the little end and closeups of the bearing supports for the two ends. Keep in mind. 1. the shaft of the rod should be parellell to the weighing scale. 2. each end should have some type of support to minimize the friction of the supports and the scale itself - especialy the big end. In this case small bearings. 3. the weighing spot on the scale should be in the same spot each time.

it wont let me add photos. find out problem and load photos later. ken

[kenparker]

this little laptop gives me more grief than all the Model A's I have put together.
Finally here are the pictures I promised. ken

[BillLee/Chandler, TX]

RE: "good enough".....

What were the Ford specs for piston weight and variance within an engine?

[Tom Wesenberg]

Originally Posted by BillLee/Chandler, TX

RE: "good enough".....

What were the Ford specs for piston weight and variance within an engine?

See Kevin in #3.

[daveymc29]

I watched the video and didn't see how the weight of the rods is reduced (or added)
I heard of an engine builder that welded to the rod to add enough weight that he could get a set that were quite close. Several of his engines had rods go through the block.It seems to me that welding on a rod would change the molecular structure and render it prone to cracking and failure. Any thoughts on both taking weight of or adding weight?

[H. L. Chauvin]

Posted this once before, (and maybe some may consider this overkill), but after Mr. Ron Kelley balanced my counter-weighted crank with new crank gear, lightened flywheel with new ring gear, etc., etc., I went for .5 grams between overall weight differences of rods & pistons with rings installed.

There always was, without a doubt, a very definite reason as to why the Hamilton & Ball Railroad Pocket Watches were superior to and far outlasted the cheap $1.00 Waterbury pocket watches; and also there is definite a reason why Model A engine re-builders are busy dealing with the "good enough for a Model A" type of mechanics.

[Mike V. Florida]

Originally Posted by SSsssteamer

I am totally amazed about how much smoother my '31 model A engine now runs after being balanced this way.

Ever wonder how many other systems the owner would be amazed with if they took the care with those as you did with yours?

[SSsssteamer]

Originally Posted by Colonel Biggs

Where did you do the balancing on the connecting rods?

Gordon
Houston

On my connecting rods, I had three rods that were near spot on. I ground a little metal off of two of the rods. I had one rod that was way too light. I machined two flat washers that I installed under the connection rod cap's nuts. After some grinding on those flat washers, it was the same exact weight as the other three rods. I did not know about weighing both ends of the rods separately as done in the Ken Parker's reply. The way that I did it, it worked well for me this time with no rear view mirror vibration in the end. I will try Ken's way next time. In the end, the total weight of the piston/rod assemblies were all equal within 0.1 ounce of each other's piston/rod assembly's total weight. My (postal?) scale measures up to 80 ounces in 0.1 ounce increments. 2.9 grams = 0.1 ounces

[BillLee/Chandler, TX]

Originally Posted by Tom Wesenberg

See Kevin in #3.

O.k., missed that.

So.... fixing a 1.2 gm variance on our Model A pistons COULD be classified as OCD?

[Tom Wesenberg]

Originally Posted by BillLee/Chandler, TX

O.k., missed that.

So.... fixing a 1.2 gm variance on our Model A pistons COULD be classified as OCD?

I have two precision scales and will be balancing my pistons and rods when the time comes. It looked like the one ebay sale wasn't going to happen, so I bid on the second one. Of course, then you wind up with two, so one needs to be sold.

[Dodge]

Having the pistons and rods balanced is the most important part of the balance job.
Get them as close as possible.

[Colonel Biggs]

Sir Kenneth --

That's one fancy balancing rig! When you are "adjusting" the weights of the rods, are you using small drill bits -- as in the piston balancing video? If so, can this require several drill spots, or are the rods pretty closely balanced in general?

What is the reasoning for not just balancing the rod as a single entity, and making the drill spot in the center of the rod?

[H. L. Chauvin]

FWIW:

For those who may remember Mr. Ron Cloat, (Rainmaker Ron),and his Model A parts supply shop, I ordered his advertised new Model A pistons and new Model A ring set.

After placing each individual piston on my new gram scale, all four (4) pistons weighed exactly the same; and after after placing each individual ring set on my new gram scale, all four (4) ring sets weighed exactly the same.

If one weighs old former connecting rod castle nuts, and/or new castle nuts from different Model A parts suppliers, and some from Non-Model A parts suppliers, one quickly finds that castle nut can vary in weight.

Next, if one orders thin washers, (not lock washers), from different suppliers and manufacturers, one finds their weights are different.

Between swapping castle nuts and adding and removing washers, one can come very close to attaining the same weight of the connecting rods on the Babbitt end.

[Tom Wesenberg]

Originally Posted by Colonel Biggs

Sir Kenneth --

That's one fancy balancing rig! When you are "adjusting" the weights of the rods, are you using small drill bits -- as in the piston balancing video? If so, can this require several drill spots, or are the rods pretty closely balanced in general?

What is the reasoning for not just balancing the rod as a single entity, and making the drill spot in the center of the rod?

The top end of the rod is reciprocating motion, and the bottom end is rotary motion, and this is the reason to balance each end to match the others.

[Kurt in NJ]

The area highlighted in red is where the factory machines for balance, if you look at the small ends you can see the differences in the amount of metal removed, on original pistons (don't have picture ), there is a boss in the rib connecting the thrust surfaces that is machined to balance, with aftermarket pistons sometimes it is the inside of the bottom of the skirt that is machined

I once found an article in american machinist online that desccribed the balancing, the machine had a scale as a chip pan,

[kenparker]

Very interesting thread and a learning experience for me.. Finding new ways to improve some of my weighing processes. I had two scales (both from Harbor Freight) One weighed in 1 gram increments. The other in .1 increments. Knocked the .1 scale off the bench the other day and it no longer works. Gotta get a new one. The scale you see in my pictures is the 1 gram scale.

Cololenel (sp) Tom W answered the ? about why balance the end separately. Kevin shows where to cut/grind metal off the rods. My pictures below show additional grinding areas. Some of my grinding spots may not take off but 1/4 to 1/2 gram at the time. Some of the grinding only smooth out the rough casting, but sometimes that is enough. The area indicated along the shank is only the rough area of the casting seam. Never take off the sides of the beam/shank.

How much is a gram. The scale and the two cotter pins show one gram, which is not very much metal. Those cotters are 1" x .80 dia. Also one gram is equal to one standard paper clip.

[kenparker]

One more note. I get pistons from Berts or Snyders and they will usually be with in 4-6 gram of one another. The rods come from Pauls Rod Shop (somewhere in Missouri) and they are usually within 4-6 gram of one another. So, Not a whole lot of grinding to be done if you buy good stuff.
"Bout year ago a set of pistons came and one of them was 20 grams heavier than the other 3. Sent them back and new set came and all four were within 4 grams.

Also the number of shim used affect the weight, so weigh theshims with the rods.

[H. L. Chauvin]

Per Reply No. 20 above, (still have the new piston box):

Just in case anyone is interested in trying to buy (4) perfect Model A pistons that all weigh "exactly" the same ............... in lieu of some of the "Good Enough for a Model A Brands" offered ............ the pistons I bought from Mr. Ron Cloat's shop (10) years ago were manufactured in the USA by:

"Silv-O-Lite", United Engine & Machine Company, 4909 Goni Road, Carson City, NV 89706.
Not sure if "Silv-O-Lite" is still in business.

[Mikeinnj]

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Silv-o-Lite Pistons for Model A are still being manufactured . Here is the link.

https://www.uempistons.com/index.php...88e34e349e846f

[ursus]

Balancing the rod small end is difficult as the recommended area to grind is a small annulus at each side. Why not balance the small end with the pin installed and take any excess weight off the pin?

[Flathead]

Two things to keep in mind are be sure the scale you are using is accurate enough for this type of work, and since the Model A engine is low RPM a "race" type balance is not needed.

[Kevin in NJ]

Originally Posted by Flathead

Two things to keep in mind are be sure the scale you are using is accurate enough for this type of work, and since the Model A engine is low RPM a "race" type balance is not needed.

So a question, what accuracy is needed?

Ford produced rods to +- 1 gram at each end.

Balanced the crank to 1/4 oz and had the flywheel to less then .001" out of center line.

When you ask a machine shop to do the engine to Ford standards they tell you that you want a racing engine.

So what is the type balance that you suggest?

[H. L. Chauvin]

Per the question in Reply # 29:

"So what is the type balance that you suggest?

In my opinion:

1. The upper limit to Model A mechanical perfection when rebuilding mechanical components for a Model A should be equal to trying to achieve 100% perfection; and,

2. Trying to achieve mechanical perfection the first time takes far less time than the time later spent on repairing less than perfect Model A mechanical assemblies that failed.

[Flathead]

The original Ford specs are fine. My point was that balancing to a tiny fraction of a gram would not yield a noticeable difference in smoothness for a low RPM Model A engine. I am not advocating sloppy work. Sorry for any misunderstanding. YMMV

[Dan McEachern]

Not to rain on any one's parade here, but the correct way to balance connecting rods is to match balance the big end weight and then balance the rod for total weight. The reason for this is so that the rotating assembly "sees" the same rotating mass on each rod jourrnal (big end) and that all the reciprocating mass is the same. Balancing the small end of a connecting rod as shown above rather than the total weight is simply incorrect. Not sure what else to say on the subject. Dan

[hardtimes]

Originally Posted by Dan McEachern

Not to rain on any one's parade here, but the correct way to balance connecting rods is to match balance the big end weight and then balance the rod for total weight. The reason for this is so that the rotating assembly "sees" the same rotating mass on each rod jourrnal (big end) and that all the reciprocating mass is the same. Balancing the small end of a connecting rod as shown above rather than the total weight is simply incorrect. Not sure what else to say on the subject. Dan

Hey Dan,
Thanks for sharing your extensive experience and valued opinion ! Also, for making us such GREAT parts !

[BillLee/Chandler, TX]

Originally Posted by Dan McEachern

Not to rain on any one's parade here, but the correct way to balance connecting rods is to match balance the big end weight and then balance the rod for total weight. The reason for this is so that the rotating assembly "sees" the same rotating mass on each rod jourrnal (big end) and that all the reciprocating mass is the same. Balancing the small end of a connecting rod as shown above rather than the total weight is simply incorrect. Not sure what else to say on the subject. Dan

Dan, please set me straight:

If all of the big ends weigh the same, and all the rod ends weigh the same, how can the total weight of any rod differ from another?

I think I understand that if you first balance the big ends, and then start removing metal to balance the rod end that you can affect the weight of the big end. But wouldn't that imply that you should iterate measuring and balancing the two ends of the rod?

Can you direct me to any papers or website that fully explains the "balancing" of a typical engine? Perhaps some explanation of how "balancing" of the rotating mass and the reciprocating mass is achieved?

Again: not trying to contradict, just trying to understand.

[H. L. Chauvin]

Looks like if two person's heads, necks, shoulders, and arms weigh the same .... and the same two person's feet, ankles, and legs weigh the same, the guy with the 54" pot belly would weigh more than the slim guy with the 30" waist .... but what do I know about dieting and eating too many french fries.

[Kevin in NJ]

For balancing the connecting rods Ford had a fancy machine that would do both ends of the rod. They cut OD on the ends as shown in the pictures. Ford specd certain weight on each end +-1 gram. From a production stand point that was probably the most cost efficient way to have balanced rods.

From the hobby stand point, you are shooting for the big ends to be the same weight. You also need the total weight to be matched so where are you going to make that happen? You have to do something at the little end. This could be in playing with pin mass or piston mass. Your goal, I believe (and may be wrong) is to have the big ends the same on the rotating mass and the total mass be the same on all 4 assemblies. On the rods you really only have 2 places to play with weight and those are the areas the factory used.