is there anysignificant block differences between the l98 blocks and the blocks chevy was using in the 70's. i have a 350 truck block with 4 bolt mains and im thinking of putting together an l98 but it gets hard when holes dont line up..

 

roller cam and 1pc rear main seal

not sure if the metallurgy, changed
i remember hearing the old ones had more nickle or something

i think all the head bolts are in the same place.

 

All bolts are in the same place, but the rear main seal is different...one piece design on 86 and newer. Metalurgy you can check by the casting either in the front or the rear of the block, look for an 050, 010, or 020 can't remember which is high nickel but find out, if you are using an older block try to find one with the high nickel, and check the cam bore...the more centered it is the better. There are casting numbers on the flange above the transmission bolting points, get chevy by the numbers book or have a local dealership check the casting numbers to see what it came from. If you are going from a 1-piece rear main seal to a 2-piece you will also need a different transmission inspection cover if you are using one.

 

thanks alot! if i use the crank form that block would the rear seal really make a difference? is there a solid reaon i couldnt use it that way and if there is then what am i looking at to switch it?

 

If you use the crank from that block, you will need to use the old style 2 peice seal. One thing to look at is the crank itself. Some of the Chevy truck engines had forged steel cranks installed in them. You can tell if the crank is forged by inspecting the parting marks on the casting. The marks on a cast crank will be 1/4 to 1/2 inch wide. The marks on a forged crank will be "knife blade thin." There are other ways to check, but I'm not familier with them. The biggest weakness in the older blocks is that you have to run a flat tappet cam, or after market roller cam. The after market rollers are extremely expensive.

 

I think you've got it reversed. The forged crank will have a wider parting line then the thin cast crank..

 

I agree.

Jake

 

Yup he has it backwards. I find the hammer method useful when looking at a crank


Clank = Cast

Diiiiiiiinnnnngggggg = Forged

 

NO method is more fun....I mean quicker than that method.