Difference in block rear mounting on 1987-down and 1987-up small blocks.

Greetings: Can anyone tell me the difference between the earlier two piece seal engines and the newer one piece seal chevy small blocks?

Mostly interested in the difference in crankshaft flanges, bolt patterns or distance out from the block.


As you can tell, I'n not a Chevy guy.

TY, MIZ

 

The "one piece" engines-
Use a different flywheel/flexplate
Use a different crank shaft
Use a different oil pan

and quite often-
Have provisions for factory roller lifters
Have no provision for a mechanical fuel pump

There are other detail differences, but these are the most significant.

 

A "one piece seal" SBC will bolt to an earlier transmission and vice versa. You just have to use the right flexplate/flywheel for the engine.
And some of the later engines are still set up to mount a mechanical fuel pump.

Larry T

 

Mount, yes, but on some, there is no eccentric lobe on the cam to run a mechanical fuel pump. That is, if you keep the stock cam.

The face of the crankshaft where the flywheel/flexplate mounts is the same distance away from the block as the earlier models. The bolt circle on the crank is smaller (3.00" v.s. 3.58"), as is the register shoulder that the flywheel/flexplate sits on. The pilot bushing is the same.

It is important to note, as there is no counterweight on the back of the crank, on the 1987 and later one-piece seal engines, that weight appears on the flywheel/flexplate.

Flywheels/flexplates can be had in 14"(168 tooth) and 12-3/4"(153 tooth).

Everything from the surface of the flywheel/flexplate back is just the same.

Remember, when choosing a flexplate, there are two possible bolt patterns: 10-3/4" and 11-1/2". Customarily, they are the 153 tooth and 168 tooth respectively, but it is best to check. Also, there are dual drilled felexplates too.

Some 14" flywheels are drilled for the smaller clutch too. Also best to confirm.

 

Crate ones seem to always have it, and I have never seen an aftermarket one without it. I have no idea what made the distinction. I have two 1989 SBC's, one has it, one doesn't.

The 305 in my A does not. It was a TBI engine, if that makes any difference.

 

Thanks to everyone. It sadly answered my question. Miz

 

Sadly? Why is that?

 

I bought an old circle track glide. I just found out that it has an early direct drive coupler....so i must buy the coupler to fit my new late crate engine. Another couple of hundred more into the deal.

 

Thats a bummer alright ....