3.1 crank into old style 2.8 block

[FieroFanatic]

I have an older block from an 84 s10 blazer I want to put a 3.1 crank into. I have read that the crank journals are larger on the 3.1, and was wondering if anyone knew if I could have the journals turned down at a machine shop to fit into the block I have. Otherwise, I'll have to get a newer block. Any ideas? Thanks.

[SappySE107]

Get a newer block. GM made them bigger because they had a problem with them breaking. I wouldn't undo that upgrade.

[fivepointhustla]

Ditch the 2.8 they suck. The 3.1 and 3.4 are redesigned.

[bjornmk1]

redesigned ?..how's that

the cranks journals are the same from '87 and up.
oiling is also the same from that year up...

B

[Guest]

It's genrally cheaper to get a new block, than to have a small journal block machined.

[fivepointhustla]

redesigned ?..how's that

the cranks journals are the same from '87 and up.
oiling is also the same from that year up...

B

Did you read he has an 84 block that he wants to put a 3.1 crank in. Reread the original post and the confusion will be gone. The pre 87-88 blocks have small journals.

[Guest]

Not all pre87 blocks have small journals. I wuold have the journals measured first to see if you have the large or small.

Also I wouldnt' have the 3.1 crank turned down to fit the smaller block, I would have the block line bored out to fit the larger mains of the 3.1

[geoffinbc]

Not all pre87 blocks have small journals. I wuold have the journals measured first to see if you have the large or small.

Also I wouldnt' have the 3.1 crank turned down to fit the smaller block, I would have the block line bored out to fit the larger mains of the 3.1

Your are exactly right. The Changeover started in 85 with all FWD cars that recieved fuel injection.

But a 1984 S-10 2.8L is gurenteed to be small journal. And I agree that machining the block is the best way but it can't be done because the rear main bearing will not accept a one piece seal used on the 3.1L cranks. So the only way to properly do it and the least cost would be to find a block. Bare blocks can be had cheep if you have a core supplier in your area.

DONT FORGET. You need a neutral balance flywheel after this crank is installed.

[Guest]

BTY, I have indication in my GM Power Manual that the block most certainly can be resized, for the larger journals, I don't recall what they suggest for the rear main though, but do recall the mention of resizing and that it's an operation that should be performed on any performance GM 660, in refernce to the small journal blocks.

[geoffinbc]

Uhh I have the power manual (book and also online) they do say to find larger journal blocks and cranks for performance use but I don't recall they saying to modify a block. They do mention oiling modifications to the main bearings.

it also states there is a one piece lip seal avalible to fit in the rope type rear main blocks without modification. So that could be the solution to this guys problem.

However I still think a newer block is cheeper than an align boring and then a honing process.

[FieroFanatic]

Thanks for the input - I think I'll probably end up just getting a 3.1 engine and saving some trouble.