OEM Piston

Fabio566

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Oct 11, 2021
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Hello I am rebuilding my blaster after my piston exploded. I ordered a wiseco piston and it had almost one millimeter of space between the cylinder and the piston. I decided that ordering a OEM piston was the best bet. I got it and it was still kind of small but bigger than the wiseco. So my question is do pistons expand when they are in the cylinder?
 
Yes they do expand when running. I think your problem is you’re putting the wrong SIZED piston in. Really bad idea putting a new piston in a worn out hole !!

Have bore professionally measured to determine proper oversized, buy correct oversized piston, bore and hone to fit THAT piston. ALL pistons vary slightly, and cast and forged pistons require different clearance because of different expansion rate.
 
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Yes they do expand when running. I think your problem is you’re putting the wrong SIZED piston in. Really bad idea putting a new piston in a worn out hole !!

Have bore professionally measured to determine proper oversized, buy correct oversized piston, bore and hone to fit THAT piston. ALL pistons vary slightly, and cast and forged pistons require different clearance because of different expansion rate.
I am using stock bore. And my old piston fits nicely. I ordered the exact same OEM piston.
 
Piston sizes aren’t all that consistent. They vary a bit. My son got his banshee cylinders back marked “A” & “B”. Pistons were marked also. Obviously enough difference the machinist noted the difference.

The higher the performance, the closer the tolerances. Many cylinder/piston may be marked A,B,C (stock factory parts).

As the machine tooling wears the pistons become slightly bigger and the bores become slightly smaller. We’re only talking.0001 inch maybe .0002 but when your clearance is only .002-.003” it matters.

And that depends on what piston. A forged piston needs more to start with because it expands more than a cast piston.