512 stroker piston to wall clearance opinions

[dvw]

Most modern pistons are so close that cylinder to cylinder sizing is unnecesary. The ring changes .00314" for every .001" of bore. Quick way to check. Blocks that have been honed with a plate will so slightly different in spots. But what may have happened here? It may have had the hone dwell at the ends of the bore or over stroked during honeng. I am no honing expert. But my good friend is. He has repair more than one hone job. Bestt o call the shop and ask. I've sent stuff back when I thought it wasn't correct. Times I've been right. Times I've been wrong.
Doug

 

[rickseeman]

You say you measured the piston. Where at on the piston? Did you measure where the piston mfg said?

 

[Llamaback]

You say you measured the piston. Where at on the piston? Did you measure where the piston mfg said?

Yes I measured the piston where the instructions from 440 source stated. On the Icon pistons there is a round spot with no black coating on it where you are supposed to measure.

 

[Llamaback]

Thanks for the feedback guys, it has been really helpful for me. I am not a seasoned engine builder so I am just trying to be cautious and do things right. My dial bore gauge has increments in .0005'' but I believe the resolution is really .001''. I will check things over with a ring in the cylinder and also put the piston in the bore again and see how tight it is with a feeler gauge. Based on the other work done on this block that I am not very happy with I think it will be going to a different shop to get re-honed and checked over again.

 

[JC Boatguy]

I've built engines at multiple machine shops. I've been building boat inboard Marine engines for decades. No performance engines run tight piston to wall clearances. 5 thousandths is necessary on performance applications for exactly the reason previously stated. My buddy built racing circle track engines in one shop I was at. One customer had to buy a engine every month until my friend built one, his lasted all summer in racing! He told me his secrets...he said he built it with extra clearance on the rods and nearly .010 piston to wall!!! Build your perf engine LOOSE! (Not a stock engine)

 

[Geoff 2]

The piston to bore clearance depends on the alum grade the piston is made of.....& the 'cam' ground into the piston. The piston is NOT round at room temp. The #2032 alum used today is very similar if not the same as the older TRW forged piston alum [ #VMS 75 from memory ]. These could be fitted with 0.002" bore clearance.

 

[Hemirunner]

DVW has it correct. Your block was honed with a torque plate. Depending on the gasket used with it, and the blocks cylinder wall and deck thickness, you’ll see quite a bit of bore distortion when they’re bolted on. The bore is perfectly straight once done, but distorts back when the plate is removed. You’re checking it without the plate bolted on so you see the distortion. Once the gasket is on and the head is torqued down, it’ll go straight again. I’ve honed some that distorted over .0015 in the center. Pretty common.

 

[oldkimmer]

Put a ring in it and measure gaps down the cylinder

Then u will know where you’re at. Kim

 

[Llamaback]

Most modern pistons are so close that cylinder to cylinder sizing is unnecesary. The ring changes .00314" for every .001" of bore. Quick way to check. Blocks that have been honed with a plate will so slightly different in spots. But what may have happened here? It may have had the hone dwell at the ends of the bore or over stroked during honeng. I am no honing expert. But my good friend is. He has repair more than one hone job. Bestt o call the shop and ask. I've sent stuff back when I thought it wasn't correct. Times I've been right. Times I've been wrong.
Doug

Thanks dvw, you were spot on for this. I checked it with a ring and the .00314'' change for every .001'' of bore had checking the ring agreeing with what I was measuring with the dial bore gauge very closely. I even bolted on a head with a head gasket and re-measured and the bore distortion was still there. I got got screwed in other ways from that machine shop that did the work so that took the wind out of my sails. I'm going to get back on the engine build this winter and see if I can get that block fixed at a different shop.

 

[33 IMP]

I might not bring it back to the machine shop, without talking to them first.

That said, with 2618 pistons, I'd want AT LEAST .005 P/W. I'd rather have .009 than .004 !
There is an old saying: if you build it too loose, you'll know. If you build it too tight, everyone will know.
I have run a cast piston 440 that should have been .0015, at .008. Noisy, cold piston slap, ran terrible, only 11.50s at 118. (I will admit that rings only went a couple seasons)