Weisco 250 husky piston(air cooled)

[Bigbill]

I got a free new piston with a bored cylinder. I contacted wiesco on the piston cylinder clearance. They said .002" now. What say you? And .011" to .015" ring gap.

 

[Michel Dufayard]

I got a free new piston with a bored cylinder. I contacted wiesco on the piston cylinder clearance. They said .002" now. What say you?

Weisco, Wiesco ! Dislexyc ?
Try Wiseco...

 

[Bigbill]

Wiesco, weisco, wiseco? I just wanted to see if anyone is awake?

 

[disonny]

.002 is too tight. I had a penton that was bored to that spec. It kept locking up on the parade lap at Unadilla last year. Got home and had it honed another thou and it was good.

 

[Kartwheel68]

005" ring gap per inch of bore diameter.

 

[jimspac]

I got a free new piston with a bored cylinder. I contacted wiesco on the piston cylinder clearance. They said .002" now. What say you? And .011" to .015" ring gap.

.002 is for liquid cooled engines. Air cooled requires at least .003

 

[Bigbill]

I was thinking he gave me specs too tight I did say air cooled 77 to 84.

I'm thinking between .003" to .0035" I can adjust the great driven hone to any amount. That's only .002" on a side.

There's no specs. No service limit specs.

 

[Bigbill]

I finally dusted off my measuring tools. I purchased this cylinder bored/honed with a new piston. It measures .004" clearance. I was figuring like you guys said .003"/.0035" but .004" would be the max. I think it's good to go. I didn't bore it but I'll live with it.

I think about it this way .004" is .002" on a side. .002" is one hair on your head.( they run between .002" to .0025 average) that's not much.

 

[suprize]

I have thin hair bill but then its very fit (face it who wants fat hair....)

 

[Bigbill]

I like to relate to things everyone would understand.

Food for thought,,,
I built dynamometers that had the torque of 27 Chevy 427 engines. We would put electric motor against electric motor testing the torque capabilities and torque curve for elevator motor new designs. 27 427 bigblock chevy engines.

 

[Bigbill]

There's rebuild specs in the technical section here. The specs are .0035" clearance.

 

[Kartwheel68]

That is for a stock piston, the clearance is relative to the material of the piston.

 

[Bigbill]

I feel safe with the wiesco piston at .004" clearance in the 250 ac.

 

[Kartwheel68]

Stock Mahle and Wiseco pistons are both forged so they will have similar clearance specs, but a cast piston will need much more, probably 50% more. That was my point, the piston clearance really has nothing to do with the engine it is going in, it is tied to the bore size and the material the piston is made of.

 

[Bigbill]

In car engines forged pistons expand more the forged pistons get .005" clearance while the cast pistons get .002" clearance.

 

[Kartwheel68]

Yes, you are right I had it backwards, cast expand less. The point is the clearance given by Husky in their manual is only useful for the stock piston or a piston of he same material.

 

[Bigbill]

I'm ok with .004".

 

[Kartwheel68]

Nothing wrong with a little extra clearance on an air cooled engine.

 

[jimspac]

.008 clearance on my 84 250WR engine when I got it even though it ran only showed 100 psi on a compression test. I am sure the rings were worn as well. I have since found there was a trend among POs of that bike showing that topends were neglected to the point of having a piston skirt break off and fractured the 250 web in the crankwell. Because of the 430 wall being intact there was never any pressure loss

 

[Bigbill]

Well I have a few 78/79 250 engines a wr and cr. Both will get new crankbearings, new seals, bored/new piston and gaskets. I like to rebuild it and forget about it. Crankshaft inspected for play and the tranny inspected. I have a few 390's and 430's to rebuild too.