The Stovebolt Site Forums The Shop Area Engine Shop GMC rods - what do I have?

I have a set of new military rods that I thought they were for a 302 with the .999 pins THEY AREN'T, the pins are smaller like .975. is this because they are new and need reamed, or can these be reamed out to the .999???
Jay D.

What is the casting number on the rod?

I did a bunch of research into the two different sizes of GMC rod small ends & piston pins and posted the results in the "parts wanted" portion of this forum back in December of last year. We found the necessary rod and I updated the post to "found" which caused it to be eliminated. I no longer have the information either, but I am sure it would answer the question. I have sent an email to the guy I was helping to find a rod pin asking if he still has the details.

If I remember correctly, the rod had the same casting number for either size little end.

Question for Admin, Global Mod and Mod: Can a deleted post to the parts wanted section of the forum be recovered? Post in question was by me on Dec 28, 2024.

According to various GMC Maintenance Manuals:

In 1952 engines, 228, 248 and 302 engines all used a pin with a diameter of 0.9898" - 0.9900" with oversize pins of 0.005", 0.010", 0.0015" and 0.0025" (Comment by Hanlon -- I'm guessing that those numbers should either be [0.0005, 0.0010, 0.0015 and 0.0025] OR [0.005, 0.010, 0.015 and 0.025] with the 1st set most likely. The machinists in the audience will weigh in.) Pins vary in length according to piston diameter.

US Army Tech Manual TM9-8025-1 "Ordnance Field and Depot Maintenance" dated May 1958 has the same pin sizes. I don't know when the Army quit purchasing new vehicles with 302 engines, but the next paragraph shows large pins for civilian 302 engines starting in 1956.

In 1956-1960 engines, 270 and 302 engines all used a pin with a diameter of 1.0523-1.0525". Pins vary in length according to piston diameter.

An interesting note is that in 1955.2 270 engines used one part number for the piston pin, while in 1956 270 used a different part number. Same for 302 engines. The Master Parts Book for 55.2-60 shows this, but does not give diameters.

I don't find any GMC pins in the .975" neighborhood that Jay D has.

Questions for Jay D: What is the width of the rod bearing in these rods? Does the locating tang of the bearing fit the notch in the rod correctly?

Bill - Sorry to say but deleted posts can't be recovered. On some rare occasions a peek in the "Way Back Machine" web archives searching Stovebolt.com might be able to locate and read what was once posted, but in this instance no luck. The last time the "Way Back Machine" captured a snapshot of the Swap Meet Truck Parts Wanted was back on 28 May 2023. Even then, there is no snapshot of the individual posts, just the sub-forum list page. Sorry.

Bill, you got to where I was going way more eloquently, lol! With a casting number, we may be able to sort out what he has there.

Casting number coming tomorrow...
Jay D.

the new rods in question, casting number is 2185419. i also have a used set with casting no's 2341204 they need pin bushings. any help identifying the new ones no. 2185419 would be greatly appreciated.
Jay D.

The 5419s are what I have in my 261 and they were .990 pins. The small end did get a bronze bushing and you finished the bushing for the .990 pin.

jay d - I think your rod casting number should read "2135419" according to this GMC Casting Number resource page. It does say .990 pins.

My 2135419 rods out of my military 302 has the .990 pins.

Just be careful that you get the correct crank bearings for these rods. There were 2 different width bearings used for this same casting rod. That’s the research that Bill Hanlon and I went through together trying to find the correct bearings for my rods. It was confusing because we discovered that the rod casting was the same, externally the rods were identical (as they should be, being same casting), however they were machined 2 different sizes for two different width bearings for the crank.

I can go into this deeper if you need, or provide measurements for the two different sizes if you need to figure out which ones you need.

Jake, if you could supply bearing measurements and how to identify what size i have and what i need for my rods the 5419 ones. i have a crank i bought from a rural fire station it was a spare crank for an old fire truck supposedly a 302 i'm trying to put together a 302 with a bunch of spare parts that i have. speaking of the 5419 rod i'm sure the bushing can be reamed to fit the .990 pins or posibly buy new bushings i would like to use them. and THANKS I'M IN NO REAL RUSH....
Jay D.

JayD: Same link as Dan has in the post immediately above this post shows the 2341204 rod to be a "late 302" using a 1.050" pin. My GMC parts book shows this rod/pin combination is used on 1956-60 270 and 302 engines.

THANKS Bill that helps. i think i'm going to use the 270. just to expensive to build the 302 starting where i'm at. i have everything to do the 270 other than haveing the 2341204 rods rebuilt. just need to make sure all the parts i have are compatible, like rod bearings. i kinda thought all 270 and 302 were the same as far as bearings. I have Seal Power CB 427P.20 rod bearings for the 2341204 rods
Jay D.

Hi Jay, attached are 4 photos of the two different width bearings for the 2135419 rods. Basically one is just a tad wider then the other, and also the “tang” that locates the bearing in the cap and rod are different widths as well. It’s hard to tell which is which if you only have one or the other on hand to look at, but seeing them side by side it’s pretty obvious one is wider than the other.

The wide bearing measures (with digital calipers) roughly 1.206” wide, with a tang width of 0.227”.

The narrow bearings measure 1.109” wide, with a tang width of 0.150”.

I also have a 270 and like yours, my 270 uses the 2341204 rods, with the larger 1.053” diameter pins.

Let me know if you need anything else or if I can help in any other way.

THANKS that explains it well. just what i needed.
Jay D.