Can you tell if a block has 1 or 2 piece rear seal without opening it up???

codfish · May 18, 2023

I’ve read that a pass side dipstick is on a 1 piece block, and a driver side dipstick would indicate a 2 piece rear main seal.

This always the case? Casting numbers on my block are darn near impossible to read. Was told it was a 444 replacement block??

I’d like to order parts and have them on hand before I dig into it.

Thanks as usual.

Codfish

fast 99 · May 18, 2023

2 entirely different operations. 1 piece seal remove tranny, 2 piece remove pan. If motor isn't original really need those block numbers. 86 and newer is 1 piece with smaller flywheel bolt circle.

DoubleDingo · May 18, 2023

Someone with a ton more knowledge than me will chime in, but I don't think you can go by the dipstick location. My engine is passenger side dipstick and has a two piece main. The engine is the factory engine that came with the truck in 1981.

Bennyt · May 18, 2023

You can pull the inspection cover. The 1 piece has an aluminum plate that would be visible.

What parts are you trying to order?
Other than the seal and oil pan gasket, you'd need to tear it down to know bearings/ rings, etc

Bextreme04 · May 18, 2023

You don't even need to pull anything... the oil pan will look different on the back between one piece and two piece seal. I found these specs on a corvette site.

Two piece seal pan measurements:
1.720" deep from the block mount surface to the main seal OD radius,
4.375" across, left to right, horizontal

1 piece seal pan (stock 1996 pan):
2.25" deep from the rails to the seal OD
5.25" wide across at the seal

Radiohead · May 18, 2023

I was thinking of looking it up on Rock, NAPA, Autozone, etc and seeing what it calls for.

Bextreme04 has an interesting method.

Rickf · May 18, 2023

Do the one piece blocks have a mechanical fuel pump?

Bextreme04 · May 18, 2023

Radiohead said:
I was thinking of looking it up on Rock, NAPA, Autozone, etc and seeing what it calls for.

Bextreme04 has an interesting method.

The problem is that he has nothing to look up if he doesn't know what he has installed. The timing cover will determine whether it is a narrow or thick front seal pan and the one piece seal also makes for a different pan size at the rear. The only way to know what you have is to read off the casting numbers and dates or to measure what is on there.

Bextreme04 · May 18, 2023

Rickf said:
Do the one piece blocks have a mechanical fuel bump?

yes. 86 and later were one piece rear main seals. 86 and later blocks can have a mechanical fuel pump boss in almost any state of finishing, or no mechanical boss at all. If there is no boss, or it is unfinished(not final drilled), then it is 100% a one piece rear main. If it is a finished mechanical boss and hole, it could be either.

codfish · May 18, 2023

Thanks

I’ll check the pan dimensions tomorrow

Just looking to buy a gasket set to seal up a few external leaks, rear seal being one of them.

Codfish

fast 99 · May 18, 2023

If pan is pulled get a 1-piece gasket. They are more expensive but much less prone to leaking, especially in vehicle.

Bextreme04 · May 19, 2023

I second the one piece felpro gasket, but be sure you measure FIRST. All one piece rear main engines have the thick front seal(or did from the factory as long as no-one swapped it to an early timing cover), but if it is a two piece rear main it can be EITHER a thin or thick front gasket. The difference in the pans is very noticeable, and is easy to measure the difference on. Summit has a page with measurements for the thin and thick front seal.

roundeyed sqbdy · May 22, 2023

Easy; if it leaks it’s a 2 pc seal, if it don’t leak it’s a one pc. (86 or newer)

84GMCSierra · Aug 11, 2023

My 84 Sierra 2500 has an aftermarket engine. It was quite difficult, but I managed to get the casting number off the back of the block as well as the number on the front
Front number is: MC25353 Rear casting number is: 10066036. Can y'all tell me if mine is a 1 piece or 2 piece? Thanks

Bextreme04 · Aug 11, 2023

84GMCSierra said:
My 84 Sierra 2500 has an aftermarket engine. It was quite difficult, but I managed to get the casting number off the back of the block as well as the number on the front
Front number is: MC25353 Rear casting number is: 10066036. Can y'all tell me if mine is a 1 piece or 2 piece? Thanks

Three seconds of google search says its a 2-piece.

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Can you tell if a block has 1 or 2 piece rear seal without opening it up???

codfish

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fast 99

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Radiohead

Reducing tire diameter 1000 revolutions at once

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codfish

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