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1G Piston to cylinder wall clearance

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SasaniFab

Proven Member
2,433
782
Dec 1, 2013
Mexico, Connecticut
THis topic has been discussed a bunch of times. My friends came over recently and we discussed the specs they planned on running for their new build. The ptw clearance ended up being over .008 with ring gaps in the 30s . I don’t think this is a good idea even when using forged internals. Have any of you heard anyone running this wide of a clearance and been successful?
 
It depends on the piston. Not just material, but design.

A slipper skirt piston will flop around a lot more than a full round. The amount of “barrel” to the shape matters a lot to.
 
They are standard Arias pistons, that seems like a lot of clearance, at that spec I can’t imagine you need to file the rings.
 
You could expect collapsed skirts or cracked skirts and oval cylinder walls with that type of clearance, thats way too much.
 
Just for reference, I built a Small Block Chevy Corvette 327 back in the 80's. Didn't have the $ to bore and get new pistons back then. One cylinder had .011 PTW clearance and others were well beyond normal but that was the largest PTW. It had factory cast 11:1s and the skirts had been knurled to bring them back out a bit for less slop, needless to say it should have been bored and new slugs.
I ran that motor to 8k in my 1973 V8 Vega, threw a 150 NOS shot on it and it never gave me any problems. Ran great and really never even used oil.
I agree with others that .008 is to much PTW but wanted to tell the story so you know that they will run but it is a crapshoot on if it will hurt pistons under pressure. Since a SBC piston has more of a skirt then a DSM piston, it held up and didn't rattle around like a DSM piston will.
Here was the car it was in, circa 1985.
Pops
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Oh the Vega and the Pinto, what were the companies thinking back then? they did end up being good for engine swaps though I guess, you see them with big hp engines at every track, they should have just made them with V-8's when they were new, then there was what the Vega Cosworth or something? some high performance version?
 
And I thought .005 was a lot of clearance, I’m looking forward to seeing what happens when they start the engine. The real problem around here is that if you are looking for machine work done your going to wait 2-3 months. They didn’t wanna wait that long so instead of over-boring they honed with a torque plate.
 
And I thought .005 was a lot of clearance, I’m looking forward to seeing what happens when they start the engine. The real problem around here is that if you are looking for machine work done your going to wait 2-3 months. They didn’t wanna wait that long so instead of over-boring they honed with a torque plate.
2-3 months is the norm for about any machine shop in the summer, maybe even in the winter around here, that kind of stuff needs to be planned and the block dropped off asap when your planning a build of any type, people are too impatient these days.
 
2-3 months is the norm for about any machine shop in the summer, maybe even in the winter around here, that kind of stuff needs to be planned and the block dropped off asap when your planning a build of any type, people are too impatient these days.
My machinist usually can have stuff back to me in 2/3 weeks
 
We have alot of dirt tracks around here and my machinist is a good month or more on wait time also. Alot of LS stuff in that place and a big old Buick straight 8.....
 
That is a very large PTW. i target .0045 normally with a build that will be seeing some serious duty. I have heard of people running .005ish, but never that large.
 
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