Piston/wall clearance spec

[Stevehose]

After 2 months, my pistons are arriving today from JE, and they were very good about communication during the process (I bought them through Top End in CA). They are recommending piston/wall clearence of .003" to .0035" which is .076 mm to .09 mm. They are forged pistons. They are saying to bore the block to exactly 89.5mm and the clearance is built into the piston.

The manual states .040 mm which is .0016" and the original pistons were cast.

So basically the clearance is roughly half as much in the manual as suggested by the manufacturer.

I have read that forged pistons can knock during warm up due to the clearances being too much, or do they need more clearance than cast in order to expand?

Any comments/suggestions about which spec to tell the machinist? Thanks.

 

[Larry Louton]

I would ask for clarification as to Bore and finish hone to 89.5mm and measure for clearance at that point. If you want to hear piston slap first hand, I'll bring my Jaguar over and return for a cold start the next morning. It will shiver your timbers. But it has been three years, doesn't use a drop of oil. Forged JE pistons.

Larry Louton

 

[M-tuner]

installing uncoated pistons is a thing of the past, you can have the abraided by. line to line coatings they will not make noise, its a graphite as used by Mahle in their race pistons, and nascar, top fuel, imsa