Piston & Connecting Rod Weight Matching

[Ron/IA]

I am doing a little research into the history on how the Model A engine was designed and built. I am currently looking into how the engine was balanced.

I know that the crank did not have counter-balances, but that Ford would design and build the pistons and connecting rods to plus or minus 1-gram. I am not 100% sure the 1-gram parameter is correct, but I believe I read that somewhere. (If I am wrong please correct).

I have the means to weigh said pieces to the 1-gram figure, but here is my question. Where on the piston or the connecting rod do you remove material? Thus bringing the weight of each to match. I just haven’t found any info on this yet.

I can weigh each connecting rod for total weight, and the weight of each end. I realize the crankshaft end of the rod is more important to match than the piston end because the rod end is rotating around a diameter; whereas the piston end is reciprocating (plus the crankshaft end is larger). Would it be worth matching the piston end of each connecting rod?

Finally, did Ford (during the engine assembly process) spend the time and resources to match these pieces when being built? That info I have not been able to find yet either.

I look forward to others ideas and opinions. I currently have a set of pistons and connecting rods I can work on.

Thanks, Ron/IA

[Kurt in NJ]

Ron --from what I have found ---the balancing machining areas are highlighted in nail polish ---while being balanced the machine weighed the chips so the amount removed was known.

the + - 1 gram is real, I have weighed boxed sets of NOS, the set differences on the 2 sets were less than 1/2 gram, each end, and total, a set of V8 (21A) rods were the same weight( less than 1/4 gram) that I recently bought at Hershey--

Original boxed sets of pistons---well the 1 set that I have are 1 gram, the 25 or so random centerlock, and endlock pistons no matter what oversize have all been within 5 grams ---from looking at various pistons the weight was machined at the bottom of the skirt

I have 5 boxed sets of 60hp pistons -- 1 gram differences in the set, 3 sets of rods--within 1/2 grams in the set

I think that on the production line the parts were divided into groups--those groups were fine tuned into sets

One of my projects is to convert what was once a pipe threader that was converted into a welding rotater to the additional uses of a balancing machining station--and a oil groover ---it is in the design/parts gathering stage

[H. L. Chauvin]

Hi Ron,

Maybe I was lucky a few years ago, but I bought new pistons & new rings from Mr. Ron Cloat, (Rainmaker Ron), where all four (4) pistons & all four (4) sets of rings weighed exactly the same.

Next bought different weight castellated nuts from several Model A vendors, local old time NAPA, & had many from former engines all of which had slightly different weights.

By selecting nuts & adding a few single, special Grainger washers, I was able to have everything balance to within a 1/2 gram.

Someone had already balanced top half of rods by removing material with what appeared to be a file.

[Ron/IA]

Kurt - Thanks for the info. You stated the pistons are machined at the bottom of the skirt. I am guessing all the way around; not just say a spot on one side, and a matching spot on the other.

The picture of the connecting rod is very informative (as they say, a picture is worth a 1000-words).

Your welding rotator/balancing machining station/oil groove maker sounds interesting.

[Ron/IA]

H. L. - Thanks for mentioning the castellated nuts. My mind hadn't picked up on that yet.

The rods I have are remanufactured from a source (reliable) our local parts vendor carries. It will be interesting to see what they weigh.

I am still interested in how much work, time, and method the Ford workers put into making these sets. Do any of you FoMoCo historians have any info?

[Kurt in NJ]

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Once online there was a link to American Machinist magazine that could be read online, in the "T" years there was a whole description of the Babbitt process --showing the large air hammer used for peining ---the design was such that it would leave the same marks that I have on NOS "A", and "B" caps ---another was a picture of parallel lines of weight sorted parts, I have been building several sets of V8 rods, they seem to fit into 5 baisic weight catagorys, the boxed set I got last Hershey had the bottom rod rusted, my random loose rods collection had 3 rods of the same weight class as the box.

I will take some of the pistons out, I am going to my playground soon, will take some more pictures for you

I suspect there were automatic scales that sorted rods into classes that a few grams removed would make groups of 1 gram easy--

In the V8 club magazine there was an article about fitting valves, the clearances were checked 3 times I think, valves were divided into length classes and just picked off a rack ---they wern't custom ground for each engine.

With Ford, the skill of "fitting" parts was taken out of the assembly part of operations, the fitting was done in the manufacturing process by holding very tight tolerances --ones that are hard to duplicate now it seems.

[Kevin in NJ]

Here is the rod print that was posted in the past on this board.

As I understand it:

Ford put the tightly matched sets of pistons and pins on the rods and reweighed them. There were 4 bins and any 4 piston rod units from one bin would be within 4 grams of each other.

That coupled with crank machined to super high accuracy swinging a well balanced 60lb flywheel that was basically on center.

All comments on those who have very low mileage cars were that they did not have much vibration. They are very smooth running engines.

A lot of little details were put in that "simple" engine.

[Ron/IA]

Kurt & Kevin - Thanks much for the information. I do understand that Ford held parts to very tight tolerances, and can see where that would lend itself to less vibration.

I saved the rod print to my files.

[Bob Johnson]

I heard (i can not remember where) that the rod weights were adjusted by removing material on the ends. They had a machine somewhat like a pencil sharpener that would grind off material. The rod was weighed to determine how much material was to be removed. The grinding machine had and adjustment which was then set to remove the correct amount of material. You can see in the picture the areas that had material removed. If you look at original rods you will notice that the edge of the area that was ground is located differently in each rod.

Bob

[Ron/IA]

Bob - Very interesting! Now I want to see the machine-like-a-pencil-sharpener.

[J and M Machine]

I believe that the spec on the rotating assembly is about 4 grams.
Once in a while we get model A engines that are being rebuilt for the first time and after measuring the rods although worn out do come close to 4 grams.

However when remachining takes place the amount of babbitt changes in each rod so then they have to be rebalanced.
Same goes for the pistons as you can see the inside boss gets machined.

Also the crankshaft is spun and also flywheel/clutch.
All of these parts were balanced at Ford.
Unfortunately after some 80 years who knows what parts have been swapped out.
Best guarantee for a good running engine is to balance it.
http://www.jandm-machine.com/balancing.html

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[Ron/IA]

J and M - Thank you so much for the pictures. They really tell a lot. Machining the inside boss of the piston is something I (being an amateur machinist) wouldn't have thought of.

[Marco Tahtaras]

Originally Posted by Bob Johnson

I heard (i can not remember where) that the rod weights were adjusted by removing material on the ends. They had a machine somewhat like a pencil sharpener that would grind off material. The rod was weighed to determine how much material was to be removed. The grinding machine had and adjustment which was then set to remove the correct amount of material. You can see in the picture the areas that had material removed. If you look at original rods you will notice that the edge of the area that was ground is located differently in each rod.

Bob

That information (though not quite that description) came from me as did the Conrod drawing and the crankshaft data. I started posting this stuff about 13 years ago when the majority of folks still believed the engines weren't balanced at the factory.

There are a couple of points from the past that are worth repeating. First, initially Ford balanced connecting rods in sets of four. They stressed to the dealers that if one rod needed to be replaced then they MUST replace the entire set of four.

Beginning with engine # A100000 Ford installed rods balanced with a revised method which provided that all rods produced were within the same weight specification. From this point forward engines could be repaired by replacing only those rods needed without disturbing the balance.

Second, due to the method of grinding the rods when balancing, you can always tell if the cap is original to a particular rod. Changing caps on rods can, and likely will change the weight of the large end even more than the variables in new babbitt. I will never consider working with a rod that does not include it's original cap. As an interesting side note, I discovered not long ago that Ford wouldn't either. They made it clear to dealers that when returning connecting rods for exchange/credit, no credit would be given for rods without the original cap as they were deemed "unserviceable".






----- Crankshaft:

[Ron/IA]

Marco - Thank you for the information. I can see you point that non-original caps on connecting rods could alter/change the end weight of said rod.

Thank you so much for the writing and drawings.