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Wed Feb 14, 2018 11:11 pm

I'm running 96mm hypereutectics in a T1. The 94mm AAs run around .0028" to .003". I used the percentage from the 94s to figure that I need .0032" clearance. Is .0032" adequate clearance?

Wed Feb 14, 2018 11:30 pm

Sorry I did not get to your question in my PM. EMW is one of the firat aircooled groups that Keith Black made HE pistons for. They have a lot of experience.

Here is an interesting resource:

http://www.hughesengines.com/TechArticles/2clearancerequirementsforhypereutecticpistons.php

Note if you scroll down that they recommend around .003"+....but that is for....I interpret.....a sand rail application.

The HE pistons have less expansion.....supposedly. I would have a serious chat with EMW. They have a lot of experience. Ask them for exactly what application they think their tighter piston to cylinder clearance is best for. Ray

Wed Feb 14, 2018 11:41 pm

Yeah .003 sounds about right.
Or.... I'd say, at least .0015 more than the minimum, if you are adapting it from watercooled normalish engine.

With any piston the clearance will depend on the design of the piston, and cam grind on it, so.....hard to say for sure.
What is the piston supposed to fit?

Thu Feb 15, 2018 7:22 am

It's either a domestic piston, and he paid Silvolite to machine them for a different pin size or a completely custom piston. I found a piston with the same specs, but with a larger pin, so that's my guess.

Ray, I actually walked-in and spoke with him. He mentioned that he runs .002" in Buses, and they should run hotter than my T1. I measured .778" halfway up the skirt, and he has his T4 barrels machined for .780".

It is possible that his pistons don't expand as much as an AA, but I feel like I want to err on the side of caution and do .003".

Oh, btw the skirts are uncoated. Should I use some sort of friction coating?

Thu Feb 15, 2018 5:37 pm

Sounds good.
IMO, don't bother with coating the skirts.

Thu Feb 15, 2018 7:20 pm

Great! Thanks! I called today to ask for an extra thou.