SBChevy Engine Types

[Chris Hill]

Just curious, but when did Chevy do the following items on the small block?

1. One piece rear main seal
2. Flat tappet to roller tappets
3. Change intake manifold bolt patten on the middle bolts

The reason I'm asking is my father-in-law is repairing a 305 marine engine and the block is a one piece rear main seal with a flat tappet cam. I did not think they made those as the one piece seal and roller tappets were intoduced at the same time.

Thank you,

[Tim H]

I believe that the one pc. rear main seal debutted back in 1988. There were truck and marine engines that were one pc. with flat tappet cams for years... something like 1988 to about 1995 or '96. The car engines went to roller lifters back in '88 or '89. As far as the angle on the intake bolts , pretty sure that came about the same time as the 1pc rear and center bolt valve covers also 1988 ?.

[NovaMan]

All that stuff happened in 86-87, but not all engines got roller lifters. My 87 truck motor had a 1pc rear seal, roller lifter spider bosses (not drilled), the goofy intake bolt angles, centerbolt valve covers, and a tiny little flat tappet cam. It also had a crack, but I don't think that was factory.

[greg fulk]

chris dad's 86 chevy pick-up had a one pice rear main with a hyd flat cam & regular valve covers? this was a 4bbl 3 on-the-tree manual!

[Chris Hill]

Greg, your close. It's a one piece rear main seal (86-up), q-jet, flat tappet cam (85 & 86), and center bolt valve covers. I think all the 4.3L have center bolt valvecovers (85 and up). The intake change is not an issue as the 4.3L started in 85.

Everyone, thanks for the info. I did not know the marine engines had flat tappets and one piece rear main seals.

Thanks,

[Adger Smith]

Chris,
The cam profile is usually not the same as truck & pass cars. It depends on the marine package & who did it. I have been told that a lot of the marine conversions were done by contract. GM furnished the parts.You can find the Date code cast on the block & heads & get a good feel for the production date.
Adger

[SSDiv6]

Originally Posted by Adger Smith

Chris,
The cam profile is usually not the same as truck & pass cars. It depends on the marine package & who did it. I have been told that a lot of the marine conversions were done by contract. GM furnished the parts.You can find the Date code cast on the block & heads & get a good feel for the production date.
Adger

...and a lot of marine parts have better performance than the OEM passenger car parts. One example is the Chrysler marine 318 engine. The intake manifold used is the same single plane intake used in the "D" Dart.



As a matter of fact, some years ago I was looking at a few Chevy NHRA Blueprint Specs, and found some of the GM marine intake part numbers used on the 305 and 350 engines.