VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 1938 216 Connecting Rods

The parts books show various connecting rod casting numbers were used over the years...

Are all rod casting numbers interchangeable (in full sets of 6)up to 1953ish or are there any casting numbers that will NOT work in my 1938 216 (block casting date December 1937)?

Thanks!

1937-47 rods are all the same. 48-53 are different.

The 1937-47 rods could have a forging number of 838389, 839558, or 3835184. It changed during the years.
The most desireable dipper to use is the 3835884 that came out about 1947. It has a much wider mouth to better "catch" the oil stream at higher speeds. It covers 1937-1953.

I would also advise checking the weight of the rods that you are using. I have found the weigths of the rebabbited rods to vary greatly. I would suspect you are balancing the engine.

Thanks!

I indeed have the wider dippers and yes, it's the balancing that is causing grief now, thus my verifying which rod casting #'s will work. The weights seem to vary by almost 20% with some rods so I've found a guy with many, many rods and want to get 8 or 9 rods so I can find the best 6 matches.

Alternatively, does anyone have a set of 0.010 rods with similar weights to sell?

I also have several sets that I could consider machining for insert bearings but I really want to stick with the original technology. Is there much difference in wear characteristics between modern insert bearings vs rods that were re-babbited 30-40 years ago?

So just to clarify; only these 3 casting #'s will work for 37-47: 838389, 839558, or 3835184?

Thanks again!

Tim,
Yes, those are the only forging numbers that appear in the parts books.
At one time the trucks larger than 1/2 ton had rods with a different part number than the cars. I have never found a reason for this and they all shared the same forging numbers. Those trucks did have a heavier, stronger piston. In the later years the same number was used for all '37-'47 rods.
Chevrolet sold only standard size rods. Any under size would be rebabbited after market. The Chevrolet rods had the babbit spun in and they were very durable. I would guess most of the recondition after market were just poured babbit. I would not recommend going smaller then .010" under size as the babbit just gets too thick and compresses with use, especially the softer babbit some used. Years ago in the dealership we would have a machine shop come in and turn the crankshaft right in the car if it was just one journal and not #1. It would be a burnt out rod and they would need to go to .030" or so. They would slip in a new rod from the bottom. After about 5000 or 10,000 miles the car would be back with the rod loose. The thick babbit would be compressed. The advantage of the insert is for the larger under sizes the insert is thicker and the babbit stays thin.
I have never had a rod problem with babbited bearings and prefer them also. We had very few burn out when the cars were newer and if they did it was usually caused by poor maintence. The pre1948 may have required adjusting evry 50,000 miles or so but that was about all.
The factory selected rods and pistons to be installed in an engine by their weight. They considered that balancing yeas ago. Once one of the pieces were replaced the balance was completely lost but never seem to be evident and no one worried.

Many thanks!

Very interesting story about machining while still in the car!

With all the years these engines were built, I'm surprised there are not more casting numbers that will work...

I've been unable to find a single rod casting number 3835184 to complete my set. I'd prefer all the same casting # so had hoped to find any size 3835184 and get rebabbited as necessary but no luck thus far.

Is there any problem with using more than one casting number as long as they are weighed/balanced? I almost forgot to mention that the 3835184 casting has a MUCH bigger oil hole in the big end. This oil hole is 180degrees from the dipper hole and passes from the bearing surface out through the side of the actual skinny end of the rod. Why is this hole so much bigger than the other two castings? Is it a desireable modification?

What was different about the new version rods produced after 1947? I compared a 1938 rod to one in my 1953 engine and they "looked" identical, though I took no measurements - just curious. I know the crank is very different so I suspect there was a change to the big end...

Thanks!

I have never seen a 3835184 rod either. With that number it must have been part of the last batch of new connecting rods made for the 1937-47 engine. By mid 1950 Chevrolet sold them only as rebabbited.
There is no problem of mixing forging numbers (a rod is forged, not cast). The weight is the most important thing.
The upper oil hole in the rod is there to allow the oil picked up by the dipper to escape so new cool oil can keep passing through the bearing.
The 1948-52 rods are the same. The width of the bearing end is reduced and the thinner babbit was used for longer life. They did resist lossening for a longer period of time, often for 100,000 miles, about twice that of the 1947. The mains also had thinner babbit.
In 1953 the stick shift 235 and 216 (used the same rods) had a new stronger rod. The I beam was wider by 1/16" and the flare above the big end was greater. Was done for the higher compression ratios. After 1953 that new rod was sold for replacement in 1948-52 engines. The rod juornal width for the 235 PG full pressure was reduced in width compared to the 1953 dipper engine. The diameter of the journal stayed the same from 1937 to 1962.