Corvette Small Block Oil Pans

[Joe L.]

As most of you know, over the course of Gen I small block manufacture, there were 2 different front oil pan gaskets used with commensurate oil pan front gasket radius. For 1955 to 1974 the front gasket was 0.22" thick and the oil pan front gasket radius was 2-1/4". From 1975-91 the front gasket thickness was 0.41" and the front oil pan gasket radius was 2-3/8".

The 1975 change was across-the-board and affected all small block oil pans, not just Corvette.

Not only did the change affect small block oil pans beginning with the 1975 model year but, about that time, the change was also incorporated into SERVICE oil pans for virtually all small block applications, including all 1956-74 Corvette small block oil pans (the 1955 oil pan had been discontinued without supercession prior to 1975 so it was not included). So, oil pans with the 2-3/8" radius front gasket surface and new part numbers replaced those with the 2-1/4" radius for 1956, 57-62, and 63-74 (both 5 and 6 quart pans).

In order to accomplish the front gasket radius change, one or more elements of the progressive die set used to manufacture the pans had to changed. This is a relatively expensive-to-implement sort of thing. Of course, for any new-design pans from 1975 onward it wouldn't amount to very much. However, as I mentioned, GM not only made the change for new pans, it did it for most existing pans.

We should all know that GM doesn't institute a change like this without a reason. In this case, though, they not only saw fit to make the change for new pans, they sustained the cost of making the change for SERVICE oil pans no longer used in PRODUCTION (e.g. all 1956-74 Corvette small block oil pans).

This is something I've wondered about for years: for GM to make the investment to make the above-referenced change I figure they had to have some absolutely compelling reason to do it. However, I'll be damned if I can figure out what it was.

[Ray G.]

Re: Corvette Small Block Oil Pans

Hello Joe;
I always wondered if changing the pan lip to allow thicker rubber seal had something to do with loosening build specifications thus lowering production costs. The bolt holes also are larger.
The thicker gaskets also improved the possibility of getting a good seal to the main bearing cap and reducing oil leaks.
Is the side spray from main bearing oil pressure is a factor?
The offset front main bearings were much earlier, as I remember, and probably had nothing to do with the lip change.
My reasoning was/is in 1955/1956 Chevrolet did not understand how prolific the 265 would become and Engineering was looking for way to reduce production costs.
just my .02

[David L.]

Re: Corvette Small Block Oil Pans

Joe,

I have always thought the reason why the change was made was so that the timing cover could be removed without removing (or lowering the front of) the oil pan. However, I have never tried to remove a timing cover from an engine with one of these re-designed oil pans to test my theory.

Back in the old days (about 1967 or 1968) I installed an aftermarket 2-piece timing cover on my 1960 Chevrolet "rag top" w/283, 3-spd. MT w/Hurst Mystery Shifter. The 2-piece aftermarket timing cover consisted of a cover without the lip, an oval "ring" plate with the lip, and 2 timing cover gaskets. This way you could change the timing chain or cam without unbolting the oil pan. I'm sure you know what I am talking about.

BTW, you missed a big snow storm last week.

Dave

[Ray G.]

Re: Corvette Small Block Oil Pans

Good point Dave.
Removing a timing cover without dropping the oil pan was/is a great advantage.

[Joe L.]

Re: Corvette Small Block Oil Pans

Hello Joe;
I always wondered if changing the pan lip to allow thicker rubber seal had something to do with loosening build specifications thus lowering production costs. The bolt holes also are larger.
The thicker gaskets also improved the possibility of getting a good seal to the main bearing cap and reducing oil leaks.
Is the side spray from main bearing oil pressure is a factor?
The offset front main bearings were much earlier, as I remember, and probably had nothing to do with the lip change.
My reasoning was/is in 1955/1956 Chevrolet did not understand how prolific the 265 would become and Engineering was looking for way to reduce production costs.
just my .02

Ray------


Yes, there could very well have been some PRODUCTION-related reason for making the change. But, why also sustain the cost of making the change to oil pans that, by that time, were SERVICE-only and not used for any PRODUCTION application?

[Joe L.]

Re: Corvette Small Block Oil Pans

Joe,

I have always thought the reason why the change was made was so that the timing cover could be removed without removing (or lowering the front of) the oil pan. However, I have never tried to remove a timing cover from an engine with one of these re-designed oil pans to test my theory.

Back in the old days (about 1967 or 1968) I installed an aftermarket 2-piece timing cover on my 1960 Chevrolet "rag top" w/283, 3-spd. MT w/Hurst Mystery Shifter. The 2-piece aftermarket timing cover consisted of a cover without the lip, an oval "ring" plate with the lip, and 2 timing cover gaskets. This way you could change the timing chain or cam without unbolting the oil pan. I'm sure you know what I am talking about.

BTW, you missed a big snow storm last week.

Dave

Dave-----

Yes, I've heard before that the change might have been related to making it easier to remove the timing cover without removing or lowering the oil pan. However, as far as I can tell, removing the timing cover without removing the oil pan is just about as difficult with either front oil pan seal. In any event, I'd never trust that I was going to get a leak-free result if I lowered the pan without replacing the entire oil pan gasket set.

Also, in the vast majority of cases, if not all cases, GM does not improve SERVICE parts unless the SERVICE part is also used on current applications OR if there is some serious deficiency that crops up for a certain part. I just can't see them sustaining the cost to modify the elements of the progressive die set if the only benefit was to make timing covers easier to remove.

Hearing about that storm reinforced my personal policy of NEVER, EVER traveling to New England from November through May. NEVER, EVER, EVER.