zupta82

Hello everyone, I can’t believe it’s been 17 years since I freshened up the stock 305 tbi on my thirdgen. I been thru a lot, I can’t believe I’m 40 years old now. It’s kind of been like an old friend never letting me down. Granted it wasn’t a monster in power by any means.

One thing for sure it’s definitely not as shiny and definitely the paint and interior has seen better days. Anyway sorry for the rant, As of late I have been craving a little more power, I scored a nice 80k mile bare 350 roller block for $150 bucks. Since it’s been 17 years since I messed with the bottom end of a small block Chevy. I recall from a machinist back then, he stated that it’s not a good idea to use standard pistons in a used block. I guess it’s better to bore it out to an oversize.

This is due to the fact that the bore may have some taper and out of round. Correct me if I’m wrong, but isn’t there a service limit that allows the bore to be within a spec that does not require the bore to be remachined. Therefore I can use standard pistons. I looked inside the bores and found very little ridges at the top of the bores, of course I would have to mic them. I would greatly appreciate some help

RedLeader289

iTrader: (2)

I don't know what the spec is but I do know you can hone the bore and use standard pistons up to a point.

dmccain

iTrader: (2)

Hone it, stick the pistons in, and send it.

dixiebandit69

If you've got ridges, the bores aren't perfectly round anymore/ you've got taper.

Can you use standard sized pistons/ re-ring it? Yes.

Is this the best thing to do, since you've already got it apart? No.

Buy a cheap set of oversized pistons (I'd recommend Enginetech pistons off of Rockauto for a '97 LT1 Camaro - Better compression ratio and ring package), have the block bored and honed with torque plates, and run it for another twenty years.

If you try putting new pistons and rings in those old bores, you're probably going to have oil consumption issues.

zupta82

Ok thanks I’m definitely going to bore it!!

Schurkey

Service limit for cylinder wear for my '88 K1500 was .001.

My block was at .0015. I cleaned-up the pistons, installed fresh rings. Gave the cylinders a dingleberry-hone. So far, so good.

When I was in trade school thousands of years ago, we were told that the absolute limit for cylinder bellmouth (typical cylinder wear--larger at the top) was .007; and that was for a Grandma-goes-to-Church engine that wouldn't be expected to last a long time. As said, now the service limit is .001. I think the truth is somewhere in-between; but closer to .001 than .007.

At .0035, I'd bore it. Less than that...might depend on what I expected from that engine; and how it was performing prior to teardown.

A high-mile cylinder with a ridge can DAMAGE new rings. The cylinder and the rings wear together, the worn rings match the ridge at the top of the cylinder. New, un-worn rings collide with the ridge. Can damage the rings, can break the pistons.

OTOH, most guys with "ridge reamers" wreck the cylinders by carving-out too much material.



BEWARE replacement pistons. They are usually "destroked", an industry term for screwing-up the piston compression height deliberately. The piston will be .010 to .020 TOO SHORT, ends up "down in the hole" so far that with a typical .040 rebuilder gasket, the engine has poor quench/squish, needs excess timing advance, and tends to ping. VERIFY COMPRESSION HEIGHT, have the block decked to compensate--or better yet, have the crank offset-ground to raise the piston AND generate a few extra cubic inches.

My latest 5.7L engine--back from the machine shop but not yet assembled--has an extra .020 of rod throw (.040 stroke, .020 "up" and .020 "down") via offset-grinding and .040-under rod bearings. The block was square-decked. The additional stroke brings the pistons to the top of the block, so I can use a cheap, common ~.040 head gasket and still have near-perfect squish.