The Stovebolt Site Forums The Shop Area Engine Shop GMC 302 installing sleeves

This engine is going to require sleeves on two cylinders.
It is .125” OS so the cylinders are getting a tad thin.
Best I can calculate there is approximately..095” cylinder wall thickness before exposing the coolant passage.
Question is, how far should I bore the cylinders before installing the sleeves?
I thinking in this case I may have to turn the OD of the sleeves to fit, or order custom made sleeves.

Dave

The only way you can really tell is by having the block sonic tested. What do the other 4 holes look like. You are going to have an expensive build by the time you are done. You might be better off finding a better block.

Just buy one of the flanged sleeves I recommended, measure the OD, and bore/hone for a snug slip fit. The .125" oversize cylinders are probably very close to the right diameter already. 30 bucks for a single sleeve is not going to make anyone starve to death. I'm considering buying all of them, (and the pistons they use) in that Ebay ad just to have them on hand for a future project.
Jerry

I just bought six of those sleeves- - - -now I just need to find an engine to put them into!

GMC 302 block- - - -.020" oversize Dodge 360 V8 pistons- - - -4.25" stroke- - - - -flanged thin wall Diesel sleeves- - - - -326 cubic inches!
Jerry

Interesting!
How did you get the stroke up 4.26?
Did you stroke the crank or use a different crank?

Dave

Guess!
Jerry

An inline six 326 would be a very good argument for keeping the six versus going V8 swap. That to me, is cooler than an LS.

Well there are a number of options.
You could stroke the crank by welding onto the throws and grinding in the increased stroke.
Or maybe Scat offers a stroker crankshaft.
maybe there is a GM crankshaft that you can install that has a longer stroke, pretty common with the vintage Ford engines.
I am new to the GM six engines.

Dave

Offset grind the 270/302 crankshaft to 4 1/4" stroke length by using a 2.100" Chevy 350 V8 rod bearing. Sleeve a 7.1" H-beam Chevy big block V8 rod down to use the small block bearing. Use the big block rod bearing pinned or held in place with brass flat head machine screws as a reducer sleeve, honed to fit the OD of the 350 rod bearing. Use a MOPAR 360 piston .020" oversize and hone the flanged Diesel sleeves out about .005" to match the piston size. Use a bronze bushing in the connecting rod small end to match the MOPAR wrist pin size. Teflon or aluminum buttons in the ends of the wrist pins to keep them centered. All of the above modifications assume the machinist has FAR above average skills. Major engine modifications involving parts from other manufacturers' engines are not a game for armchair quarterbacks.

I grew up in the 1950s watching my father do "impossible" modifications on flathead Ford engines, and I've been doing similar stuff for 50+ years, so I'm definitely not smoking wacky tabaccy!

It would probably also be possible to build a 301 cubic inch / 4 1/4" stroke GMC 270 using standard bore 292 Chevy 6 cylinder pistons. (No sleeves- - - -.090" oversize) 270s are a lot more plentiful (and less expensive) than 302s!
Jerry