Oil Pan - What do I have?

[Bob S.]

Trying to dry up an oil leak at the front of the engine on my 59 I decided to remove the pan and change the gaskets. After removing the pan I discovered a considerable amount of hardened sealer on the pan lip. I removed the sealer and laid the new gasket on the pan for a trail fit (using a 1 piece OS34509T) and the portion of the gasket that goes between the timing chain cover and pan swings freely not touching the pan lip.

I took my pan over to a friend who has some original 3 step pans in his garage and did a comparison. My pan is clearly a reproduction (the engine had just been rebuilt when I bought the car so I don't know the story behind this pan). The main difference in the front of the pan is that the radius of my pan is approximately 3/16" greater than an original.

I have located a used original that I will clean up and install but I would really like to know what this pan would fit. It is a 3 step with the trap door. The only marking I can see is "220R" stamped in the center step. The entire pan, inside and out, has been powder coated black before the outside was painted Chevy orange.

Is there a SB that uses a larger timing chain cover? If anyone has any ideas I would appreciate knowing what I have.

Sully

[Joe L.]

Re: Oil Pan - What do I have?

Trying to dry up an oil leak at the front of the engine on my 59 I decided to remove the pan and change the gaskets. After removing the pan I discovered a considerable amount of hardened sealer on the pan lip. I removed the sealer and laid the new gasket on the pan for a trail fit (using a 1 piece OS34509T) and the portion of the gasket that goes between the timing chain cover and pan swings freely not touching the pan lip.

I took my pan over to a friend who has some original 3 step pans in his garage and did a comparison. My pan is clearly a reproduction (the engine had just been rebuilt when I bought the car so I don't know the story behind this pan). The main difference in the front of the pan is that the radius of my pan is approximately 3/16" greater than an original.

I have located a used original that I will clean up and install but I would really like to know what this pan would fit. It is a 3 step with the trap door. The only marking I can see is "220R" stamped in the center step. The entire pan, inside and out, has been powder coated black before the outside was painted Chevy orange.

Is there a SB that uses a larger timing chain cover? If anyone has any ideas I would appreciate knowing what I have.

Sully

Sully------

What you likely have is the GM SERVICE pan of GM #359937. This pan is very similar to your original pan EXCEPT for the front oil pan gasket radius. This pan requires a front gasket thicker than the original pan. The original gasket was 0.22" thick and the new pan a gasket 0.41" thick. As far as the Fel-Pro 1 piece gasket goes, you require the OS 34510T.

By the way, I know of no reproduction of the 3 step, 56-62 style oil pan, even today let alone years ago when the pan on your car was installed.

[Vinnie P.]

Re: Oil Pan - What do I have?

Article by Ed Lepelis on 1956-62 oil pans from the Summer 2015 Restorer

https://www.ncrs.org/restorer/1956-62%20oil%20pans.pdf

[Bob S.]

Re: Oil Pan - What do I have?

Thanks Joe. I had a feeling you would know. I should have asked sooner and I would not have bought the used pan. It is, however, correct for my car with the two-rib baffle.

[Bob S.]

Re: Oil Pan - What do I have?

I now know it is a service replacement but the more I think about it, why make a service replacement with a different dimension when you already have the original dies and now you need different gaskets? It seems it would be easier, and cheaper, to just stamp out originals.

[Jerry K.]

Re: Oil Pan - What do I have?

It has something to do with removing the timing chain cover in the early years. I think the service pan eliminated the need to do this. The front seal was the problem to get on and off. Just my thoughts.

[Joe L.]

Re: Oil Pan - What do I have?

I now know it is a service replacement but the more I think about it, why make a service replacement with a different dimension when you already have the original dies and now you need different gaskets? It seems it would be easier, and cheaper, to just stamp out originals.

Bob------

The C1 oil pans evolved over the years. There were several iterations, many differing only slightly. I believe the 359937 was based on the 1962 version of the pan, the last used in PRODUCTION. However, there may have been minor differences.

These oil pans were manufactured using multi-element die sets. To change configuration from one version to the next, it may only have been necessary to change or modify one of the elements. Obviously, the element involving the front gasket had to be changed for the 359937 pan.

The 359937 oil pan was released in 1976. By that time the last C1 oil pan, GM #3789629, had not been used in a PRODUCTION application in 12 years. There's just no way in the world that GM would have created a completely new die set for a SERVICE-only, low-volume oil pan at that time. In fact, I've always been surprised that they even went to the expense of modifying the dies for the front gasket revision. However, I'm pretty confident that, mostly, the die sets used to manufacture the 359937 oil pan were the same as originally used "once-upon-a-time".

[Joe L.]

Re: Oil Pan - What do I have?

It has something to do with removing the timing chain cover in the early years. I think the service pan eliminated the need to do this. The front seal was the problem to get on and off. Just my thoughts.

Jerry------


That's the only reason for the change that I've ever been able to come up with. I just cannot comprehend that any other "betterment" could have resulted from the gasket change. The only other even possibility would have been improved sealing and I just don't see how the slightly thicker gasket would have accomplished that.

All 1975+ small block oil pans incorporated the front gasket radius revision. So, why go to the expense of changing the die sets for earlier applications which were all SERVICE-only by that point? In fact, all of the C2 and pre-1976 C3 oil pans were changed at that time, too. All I can figure is they were tired of hearing bitching from mechanics over the need to remove the oil pan in order to remove the timing cover (an often needed SERVICE procedure considering the nylon-toothed cam sprocket used on small blocks).

[Joe L.]

Re: Oil Pan - What do I have?

I now know it is a service replacement but the more I think about it, why make a service replacement with a different dimension when you already have the original dies and now you need different gaskets? It seems it would be easier, and cheaper, to just stamp out originals.

Bob------


By the way, once-upon-a-time C1 folks used to sneer at the GM #359937 replacement oil pan. Then, about 10 years ago it was GM-discontinued. Now, they often pay big bucks to get one.