[steve25]

Here’s what the factory wanted for piston to wall clearance.
As you can see as the compression went down and the exh gas temps went up the engineers wanted more piston to wall clearance.

I would suggest to you that since you are saving money with your rebuild by not boring, that you put a bit more back in by getting a Total seal gapless top ring and then run a reverse twist barrel face moly second ring like the motor came out of the factory with.

The moly face top and second ring are why Pontiac cylinder walls last so long.

Be sure to take the hours that it will to break / lightly roll over all the 90 degree corners on all the rings .
This will stop these edges from digging into the walls and scratching them and also digging into the pistons.
Besides being rewarded with having no added ware taking place to the cylinder walls you will also have less friction and cooler water temps.

The ends of the oil ring rails being that they are hard steel are a big culprit in the scratches seen on cylinder walls.
If you do any rolling over of the corners of any of the rings then it should be these.

[gtobird]

Originally Posted by steve25

Here’s what the factory wanted for piston to wall clearance.
As you can see as the compression went down and the exh gas temps went up the engineers wanted more piston to wall clearance.

I would suggest to you that since you are saving money with your rebuild by not boring, that you put a bit more back in by getting a Total seal gapless top ring and then run a reverse twist barrel face moly second ring like the motor came out of the factory with.

The moly face top and second ring are why Pontiac cylinder walls last so long.

Be sure to take the hours that it will to break / lightly roll over all the 90 degree corners on all the rings .
This will stop these edges from digging into the walls and scratching them and also digging into the pistons.
Besides being rewarded with having no added ware taking place to the cylinder walls you will also have less friction and cooler water temps.

The ends of the oil ring rails being that they are hard steel are a big culprit in the scratches seen on cylinder walls.
If you do any rolling over of the corners of any of the rings then it should be these.

Thanks for the spec info. This reminds me of something I learned with my last engine. Originally I had it bored for 30 over pistons. The shop that did it cut and honed the cylinder walls for something other than the Old School TRW Forged Pistons I was using. I had those things in storage for 25 years waiting for the build! In the end, I had to have the block rehoned a few thousanths larger. The point I'm making is that forged pistons require a larger bore size (as shown in the chart your provided). If I could magically locate an old school set of standard size forged pistons, they might be a good match for this build. Of course, I haven't even checked out the bore size and taper yet so this is all just wishful thinking.

OJ

[Schurkey]

Originally Posted by 61-63

Check the taper in the bores... ...It had 80k miles on it and .003 or less taper in the bores

Thousands of years ago, I was in Trade School. We were told that .007 taper was the absolute limit, and only for a "grandma goes to church" engine--nothing with any performance aspirations.

The "Service Limit" for the 350 in my '88 K1500 was .001 taper. My replacement block had about .0015, I put it together and it's working fine.

There is no way I'd use plain iron rings. Inexpensive Moly-faced are as cheap as I'll go. Moly is porous, holds oil, reduces cylinder wall wear AND seals better.

Originally Posted by gtobird

I had it bored for 30 over pistons. The shop that did it cut and honed the cylinder walls for something other than the Old School TRW Forged Pistons I was using.

Most pistons are supposedly set up with the clearance built-into the piston--you'd hone to the nominal bore size, and the piston would be appropriately smaller to give correct clearance.

But I won't guarantee that all pistons are made that way. My favorite machinist wants to have the pistons in-hand so he can measure them before honing.

Rigid honing should be done with a torque plate. Dingle-berry brush honing won't need a torque plate.

Don't forget to plane the head gasket surfaces square to the crank, and to end-up with appropriate quench/squish given the compression height of the pistons you select.