Thick or thin oil pan front seal - Chevelle Tech
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post #1 of 19 (permalink) Old Jun 30th, 20, 3:10 PM Thread Starter
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Thick or thin oil pan front seal

sbc400 1971 needs a new pan gasket.
I almost bought the blue fel pro with thin front seal.

But now i read that the pan determines the gasket not the engines year of production.
I did found a how to measure and determine thick or thin but i didnt figure out if this is possible when the pan is actually installed.

Is it possible to measure the seal gap itself? 1/4 or 3/8" with installed gasket (current gasket)


Any who can clarify a bit for me?
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post #2 of 19 (permalink) Old Jun 30th, 20, 3:32 PM
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Re: Thick or thin oil pan front seal

What is the measurement of the current one = ?

Then you would likely want a Thicker one as it likely depressed when installed
or did the soaking of the Oil put it back to the Original Thickness !

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1/4 = 11.595 et / 114.28 mph


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post #3 of 19 (permalink) Old Jun 30th, 20, 3:41 PM
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Yes the pan determines it. I just had to don the same with my new motor build with new pan. You can try to measure it with everything installed to get a close figure. But pan should be off.
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post #4 of 19 (permalink) Old Jun 30th, 20, 3:50 PM
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Re: Thick or thin oil pan front seal

Unless you are buying a 1 piece gasket, they come with both end seals. If you are buying a 1 piece, get both versions and return the wrong one.
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post #5 of 19 (permalink) Old Jun 30th, 20, 4:56 PM Thread Starter
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I dont live in the US so returning items isnt really an option.

So it HAS to be measured either way with the pan not installed?
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post #6 of 19 (permalink) Old Jun 30th, 20, 5:12 PM
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Re: Thick or thin oil pan front seal

If it's stock 1971, it would be thin seal and not a one piece oil pan gasket.

The thick seals emerged in mid 1976 model year on the first "metric" motors. Most generic replacement pans are set up for the thin seal.

If in doubt you could use clay to mock it up and measure the gap.

I did a cam swap on my brand new 1976 Camaro. Went to the local auto supply who did not yet have a listing for a 1976 Chevrolet Camaro 350 timing gasket set. We all assumed that earlier years would fit. Put it all together, ran it up and down the street and it was leaking like a sieve. I did not know what was wrong with it until months and many quarts of oil later.
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post #7 of 19 (permalink) Old Jun 30th, 20, 6:30 PM
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Re: Thick or thin oil pan front seal

Quote:
Originally Posted by Alan F View Post
If it's stock 1971, it would be thin seal and not a one piece oil pan gasket.

The thick seals emerged in mid 1976 model year on the first "metric" motors. Most generic replacement pans are set up for the thin seal.

If in doubt you could use clay to mock it up and measure the gap.

I did a cam swap on my brand new 1976 Camaro. Went to the local auto supply who did not yet have a listing for a 1976 Chevrolet Camaro 350 timing gasket set. We all assumed that earlier years would fit. Put it all together, ran it up and down the street and it was leaking like a sieve. I did not know what was wrong with it until months and many quarts of oil later.
Aftermarket pans also use the thick front seal.

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post #8 of 19 (permalink) Old Jun 30th, 20, 6:42 PM
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Re: Thick or thin oil pan front seal

Aren't some people using The Right Stuff Gasket Maker on oil pans now?

https://www.permatex.com/our-brands/the-right-stuff/

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post #9 of 19 (permalink) Old Jul 1st, 20, 11:16 AM Thread Starter
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Quote:
Originally Posted by Alan F View Post
If it's stock 1971, it would be thin seal and not a one piece oil pan gasket.

The thick seals emerged in mid 1976 model year on the first "metric" motors. Most generic replacement pans are set up for the thin seal.

If in doubt you could use clay to mock it up and measure the gap.

I did a cam swap on my brand new 1976 Camaro. Went to the local auto supply who did not yet have a listing for a 1976 Chevrolet Camaro 350 timing gasket set. We all assumed that earlier years would fit. Put it all together, ran it up and down the street and it was leaking like a sieve. I did not know what was wrong with it until months and many quarts of oil later.
As far as I know, the sbc years 1955-1985
Are 2 piece rear main seal(crank bearing).

There are multiple types of oil pan gaskets.
Felpro make the blue one for both 1 or 2 piece rear main seal. But in both cases a 1 piece oil pan gasket.

Among this, also multi piece oil pan gaskets are available.
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post #10 of 19 (permalink) Old Jul 1st, 20, 3:42 PM
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Re: Thick or thin oil pan front seal

Actually there are 2 different timing cover sets, and consequently oil pan sets from '55-'85 BEFORE you get to the years with the factory 1 piece gasket set.

Excluding the one piece oil pan set retrofit (like Mahle and Victor) there is not a factory produced 1 piece oil pan gasket for '55-'85.

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post #11 of 19 (permalink) Old Jul 1st, 20, 4:17 PM Thread Starter
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Quote:
Originally Posted by Alan F View Post
Actually there are 2 different timing cover sets, and consequently oil pan sets from '55-'85 BEFORE you get to the years with the factory 1 piece gasket set.

Excluding the one piece oil pan set retrofit (like Mahle and Victor) there is not a factory produced 1 piece oil pan gasket for '55-'85.
Now i am completely lost. What about the felpro 34509T.

This is advertised as 1 piece oil pan gasket, for 2 piece rear main seal with thin front seal.

You say that wouldn't fit except if i had the victor or mahle retrofit pan?
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post #12 of 19 (permalink) Old Jul 1st, 20, 6:15 PM
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Re: Thick or thin oil pan front seal

Quote:
Originally Posted by Bart Fransen View Post
Now i am completely lost. What about the felpro 34509T.

This is advertised as 1 piece oil pan gasket, for 2 piece rear main seal with thin front seal.

You say that wouldn't fit except if i had the victor or mahle retrofit pan?
What Alan F is saying is the factory never assembled a 2 piece rear main seal engine with the 1-piece oil pan gasket.....because they didn't exist back then. The Fel-Pro and other 1-piece oil pan gasket retro-fit for the 2-piece rear main seal engines are a aftermarket invention, patterned after the 1-piece oil pan gasket that were now being used by the factory on new 1 piece rear main seal engines.

There are 1-piece oil pan gaskets for the 2-piece rear main seal engines available in both the thin front lip versions and the thick front lip versions....the gasket used must match the oil pan front lip dimension.
I don't know of a way to accurately measure the pan with it installed on the block and a gasket in the lip.
Fel-Pro 34509T fits the '57-74 thin gasket pan lip, 2-1/4" dimension.
Fel-Pro 34510T fits the '75-85 thick gasket pan lip, 2-3/8" dimension.

visually, if you look at the installed pan with the current lip gasket, and you can see about 1/8" of that front seal in the gap between the pan and the timing cover channel, it is the thick version.....if you really can't see the front pan seal without really looking hard into the point the pan and the timing cover fit together it is the thin lip seal.
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post #13 of 19 (permalink) Old Jul 1st, 20, 7:48 PM
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Some aftermarket pans will tell you which seal to use. I just purchased a new chrome pan and it stated thick seal.
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post #14 of 19 (permalink) Old Jul 1st, 20, 8:49 PM
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Re: Thick or thin oil pan front seal

Bart,
I will try to remember and look at a couple in the morning at the shop but I am pretty sure that if you can see the seal when you look straight at the front of the engine, it is the thick one. With the thin one it is "hidden" in the recess in the timing cover and you cant actually see it looking straight at the front of the engine. I should have one of each at the shop, I will try to post a couple of pictures.


Also going to mive this to the Engine forum
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post #15 of 19 (permalink) Old Jul 2nd, 20, 7:56 AM
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Re: Thick or thin oil pan front seal

Bart,
Here is two pictures of the front of a 400 block with the two different oil pans.



If you look at the first one you can see where the arrow is pointing there is a gap where you would be able to see the front seal of the oil pan gasket. The oil pan is actually lower than the front cover. This requires the thick seal.


On the second picture you can see that the oil pan is actually up into the recess in the front cover and you cannot see a gap. This requires the thin seal.
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