VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc connecting rods

I am at work on a 235 and I am having a devil of a time finding where the connecting rods are listed in any of my catalogs. The motor is from a 56 car with hydraulics. The rods have a casting number of 3836677 GM 708. I am certain that any of the rods from 54-61 will interchange including the 3701491, 3836410, or the 3836671, however I am curious to know what difference there may be between these differently numbered rods? Would it be safe to assume one could mix and match different rods when rebuilding an engine? Your thoughts would be appreciated.

I would be very careful mixing different rods. While they all might fit and function I would be concerned with the difference in weight causing a balance and vibration problem.

You do not want differences in rod weights . That would be detrimental to the balance of your online six.

I endorse previous posting, use rods with the same casting number though fully even balance can only be determined by those with the skill (my machine does any I need done). I also get them to balance the pistons as well. A full balance is not a 5 minute job even for the experienced engineer but does make a difference to running smoothness and more so at idle.
Tony

I also agree with balancing the connecting rods with the pistons.

When I rebuilt my '28 engine in 2017, I was mixing and matching parts from three different engines. The rods that I chose came from all three. They did not weigh the same and I noticed that one had a different casting number. That one was way off from the others. I chose a different rod with the same casting number and got a set that was much closer to each other in weight.

I used a cheap belt sander and a digital scale to make them all the same weight within 1 gram. As a result, the engine runs incredibly smooth.

Here's the part of the rebuild where I dealt with the weight of the rods and pistons: Resurrecting a '28 4 Banger - Matching connecting rods and pistons

Cheers, Dean

Thanks to the "ChatMasters" that have responded to my inquiry on connecting rods. I am fortunate that I do not need to replace any of the rods for this rebuild, however, I do have an assortment of incomplete sets of rods from other engines that have no mates. Ergo I will be looking to find rods with corresponding casting numbers to fill out the partial sets in my collection.

I am still perplexed as to why GM had so many different castings. It would seem plausible that the design of the connecting rods evolved with a series of improvements between 54 and 61. I am just curious to understand what those improvements might be, and if there are any significant advantages for using the later verses the earlier rods.

I worked for a Chevrolet Dealer in parts from 1950-1977 have an large collection of Chevrolet literature and never found any changs or improvements in the 1953-1962 235 conneting rods. They never were problematic. I can offer no help at this time.

Thanks for weighing in on this Gene. I agree finding rods with identical forging/part numbers would be the most desirable option, however, failing to find an exact mate for a set missing just one rod out of 6 would invite an alternate solution.

What did a GM dealer do back in the day when a car came in with just one rod rapping that needed a replacement? If the part off the shelf had a different casting number, I am sure the service department ground and polished the journal, installed the new rod with an oversized bearing and sent it out the door. Perhaps not the best scenario, however it would send the customer on his way at a reasonable cost.

I am sure that in the hands of a professional balancing company, a mixed set of rods could be individually weight adjusted on the wrist pin end as well as the journal end prior to overall weight balancing which would of course include the pistons. I will give that a shot on the next 235 I rebuild.

Hi Midi

I was going to post regarding the importance of recognizing not just the overall weight of the rod, but also the rotating weight versus reciprocating weight (big end versus small end weight) for the balance of an engine.

But I see from your last post that you've got that covered! :-)

After shot blasting and a close examination of the rod set that initiated this thread, I must stand corrected. The casting number on these rods is actually 3836671 not the 3836677 as previously noted. I now keep a magnifying glass handy on my work bench. I regret the misinformation, however I do thank all of the responders for their input.

"Back in the day" we sold very few connecting rods for the full pressure235 engines. Not like the dipper engines and thick babbitt the would compress and chip out. We were a large Chevrolet dealer in the Milwaukee area.
The only cause to replace a rod was wnen an insert turn in the rod (burmt out rod bearing) due to lack of oil. We just did what was necessary and installed a new rod. There were part number ans forging numbers changes but app;ication remained the same.

For pistons it was a different story. A "box" of 235 6 pistons (or any other engine) was sold as a matched set weight wise aand were to be installed - not just one, In actual life no one paid attention to that and we had broken boxes of pistons and would sell one for replaceent with no problems.

If I FIND ANY ROD INOF i WILL LET YOU KNOW.