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piston cylinder clearance w nicasil
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Posted by: iamjasyn

I told the guy at Millennium to put .003" clearance in my stock (270cc iron) TRX bore for a wiseco piston. Does that sound about right to you guys?

Posted by: Aceman

I can't answer your question. But shouldn't you be asking BEFORE you bore it?

Posted by: iamjasyn

Yes, the obvious answer is yes. .003" will probably be fine. I'm asking for opinions in case someone has deeper knowledge about this setup. There is a bit of a range you can run pistons at. Honda set them up I think at .0024"-.0031" and the wear limit is .006".

Posted by: 250r4life

yes that sounds about right... i have them set mine up at .0025... but .003 is fine... you want to keep them between .002 and .005, although .002-.003 is the ideal clearance...

Posted by: wilkin250r

You know, I haven't really built any Nikasil motors, but 0.003" sounds a bit big. One of the major advantages to Nikasil is the fact that you don't have an iron sleeve, it's usually coated over an aluminum sleeve. Therefore, the thermal expansion rates are the same for the cylinder and piston. This should allow you to run tighter tolerances.

What is your piston material?

Posted by: iamjasyn

Ya, I know nic is usually run on AL bores. I think the one of the large historical points for it started with Porsche back in the day. Anyway, I'm doing it to preserve my the cylinder on it's last bore because I like porting in it. That's it. I think with an iron bore you're not really going to realize any heat transfer improvements just with nic. So I basically still have to pay attention to iron bore clearance specs (forged piston, wiseco).

Someone really familiar with the setup can tell you how fine tuned you can run the piston. The tighter being that you have less oil between the piston and bore, and the looser, you lose efficiency and power. A builder on another board told me .003 is fine, but make sure the engine is nice and warm before hitting it - so it's basically kinda tight, so I'm probably where I need to be I guess. I just thought I'd open a discussion up about it.

How hard is it to replace the iron bore with an Al and still get the ports matched how they were?

Posted by: wilkin250r

quote:
Originally posted by iamjasyn
How hard is it to replace the iron bore with an Al and still get the ports matched how they were?

That's an excellent question. I wish I had an answer for you.

As for the original question, I think you're on the right track. I first thought it sounded loose for a Nikasil bore, but the iron sleeve is going to require a little extra clearance as opposed to an aluminum sleeve, and the forged piston requires a little more still because the grain structure causes it to have a little more horizontal expansion than a cast piston.

Posted by: Tech23

iamjasyn......I sent you a pm, Check your messages

Posted by: iamjasyn

Kevin. Sent a reply.
J