Cat Twenty gas cap

There were two different cap assemblies, the early one is an L1349 and the later is L1733, with the change at PL 530 and either L87 or L876, the parts book I have shows two different numbers, probably L876.
The problem is, that there is only one fuel tank assembly for use with both caps, so it would not make sense to have different threads, perhaps a previous owner changed the cap and the neck? can you read the casting numbers on the neck?

Hi Josh,
I haven't taken a close look at the casting but I will tomorrow.
My two options as I see them right now is to take one of my two gas caps and fill the threads with JB Weld then bore it to the right ID and then thread it to match the neck.

The other (and probably better option) is to machine another flange and neck to fit the current threads on the cap I have and then replace the current flange.

If I'm living right, I may be able to do this with some store bought plumbing and machine it to match what's on the tank and the rivet pattern.

On the twenty I have, the neck is a cast piece, that is riveted and soldered on to the tank, yours looks like it is pressed metal part. Seems like there must be someone out there with a rusted out tank, that has a good neck, and would part with the neck? I know those tanks are prone to rusting out.

You are right. My tank was like a sieve until I coated the inside.
It would be great to find someone that not only has the bad tank but has time to cut the part out. That's the hard part.

Tom, I should have a gas tank that the bottom is completely gone in. It is a mid production PL model. PM me and I'll get some pictures for you. Roby Whitehead

You are right to think there are 2 different thread sizes. The early tanks had the thread like yours and then they changed to the bigger thread. I know this because my neighbor has a early 20 with the different cap. The cap is made of steel with a sort of wing nut on top to get it off. If you change it it will no longer be original. If you do change it, save the neck as some one will want it for a restoration some day. - Wally

You are right to think there are 2 different thread sizes. The early tanks had the thread like yours and then they changed to the bigger thread. I know this because my neighbor has a early 20 with the different cap. The cap is made of steel with a sort of wing nut on top to get it off. If you change it it will no longer be original. If you do change it, save the neck as some one will want it for a restoration some day. - Wally

Hi Wally,
Thanks for the additional information. I was really confused because the neck assembly looked stock and original. I have located a later replacement neck that is cast brass or bronze.

The one presently on the tank isn't cast but appears to be heavy sheet steel or ?? rolled to fit the tank and riveted. The threaded neck also appears to be steel and is a much lighter gauge than the cast replacement.

If the one on my tank is original, Caterpillar really needed to change the design to a heavier gauge cast part in something that could hold up to continuous use.

I won't throw the part away but I really don't think there is much chance of locating the proper gas cap.

Thanks again,
Tom

Here is a picture of the early gas cap for the L/PL Twenties
Thanks
Ken