[HWYSTR455]

Originally Posted by scott70

.003 clearance? Is that the end gap on the lock ring after it’s installed?

There's no asterisk on any of the values, so it's not real clear, but you can't adjust the pin to retainer clearance, so...

That .003 appears to be the pin to piston clearance, the more I think about it.

Considering the materials can differ between piston and rods, it must be the value for pin to piston, and the pin to rod clearance would be dictated by the rod manufacturer.

Searching for that I couldn't find the Molnar specs for rod to pin clearance values, but you should get a spec sheet with the rods. If it doesn't have the pin to rod clearance, I say call Molnar, or even Butler.




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[Dragncar]

.003 on pin to piston is huge. The piston would flopping around..

[HWYSTR455]

Originally Posted by Dragncar

.003 on pin to piston is huge. The piston would flopping around..

Only other thing I can think of is that could be the piston to wall clearance.

That spec sheet for some reason is not making it clear to me.




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[Dragncar]

Originally Posted by HWYSTR455

Only other thing I can think of is that could be the piston to wall clearance.

That spec sheet for some reason is not making it clear to me.




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Its says "gauge point" pointing at the bottom of the skirt right where you measure piston dia.
.003 piston to wall sounds tight. But, I believe Racetech are similar to the old JE stuff and I want to say you ran those a little tighter.
Paul sells those pistons, he would know.

[Formulajones]

Icon forged pistons I just bought call for .0025-.0035 piston to wall clearance. They sure are making them tighter than they used to. I ended up with .003 right in the middle of spec so I'm running with it

Pin clearance gets a little confusing as it's not real clear. I've always had to have a new setup honed for pin clearance as they all are shipped on the tight side on purpose so this can be done. How it's explained to me anyway. And different shops seem to have their own ideas what that clearance should be depending on rpm turned and the HP being made.

[Jay S]

The .003” is piston to wall at the gauge point. Guessing the piston is a 4032 alloy to run that tight. Paul K speaks better RaceTec&Autotec than me, he can correct me.

[mgarblik]

Many posts lead to giving Paul a call. I would also recommend doing that. He sells those pistons and is familiar with their instructions. Piston to wall of .003" may be a minimum for a 4032 alloy for their pistons. Personally, I never hone a performance oriented engine to the minimum clearance. I would probably hone it to .004". But that is a machinist choice. The wire pin retainers do an excellent job retaining the pins but are a pain to install IMO. Typical Pin to rod bushing and pin to piston clearance is a nominal .001" +- .0002". Some variations are extreme heat from power adder applications, very large pins like Mopars, floaters without bushings.

BTW, buying Molnar rods for your application is an extreme overkill purchase for your application..........and I love it. High quality parts only hurt you at the time of purchase, not three years from now when something fails. You have huge safety margin with those rods.

[scott70]

Yes it has snowballed some … just like everything I do lol. I went from changing the rod bolts and checking the big end to different rods with arp 2000 already installed and converting to floating pistons . I think I paid like 260 for the rods from ace in 2012. These molnar were 730.00 and I’ll sell the ace 4130 rods,, probably not worth much. Price wise I tried to weigh it all out . It’s the same pistons going back in so pistons to wall clearance should be all good. I’m assuming the autotech pistons that are in it are for floating pistons because they came with wire clips but I can’t find them now,, probably figured I’d never use them and threw them. I did order some of the wiseco ones summit has. Overkill for sure for my application. This engine will never be built for 6500 rpm shifts. It’s the number matching 455 in my 70 gto. Where it says .003 clearance… it’s just a weird place on the paper,,, you would think it would say .003 piston to wall clearance. I bought the pistons from Paul k,, maybe he’ll see this.