Piston clearance is too small

[cmcfaul]

I broke a piston, found a perfect match new piston. However it's 4/1000 to big. It fits in the jug but there is no clearance. It's a JE piston they no longer make. Can it be machined, sanded or in any way be made the correct size. It's so close, would hate to have to buy 6 new pistons. The others are perfect.

Thanks,

Chris

73 911 e

[AlfonsoR]

I would think that you can machine the bore OD fairly easily, but there's more to just making the piston the same bore OD as the rest.

What about the ring area ODs and heights? These are very important. Under the compression stroke, the spent gas seats them (down) and then against the cylinder wall so that they seal to hold compression. There is some real science to that and if it's not the same, then you will probably have oddball wear.

[cmcfaul]

The new piston has the same casting number as the original. It's the exact piston except it's slightly bigger. The cylinders are Nickicell so I can't bore it out to make it work (that would be a bit of a jerry rig anyway). I believe that is why the remaining 5 pistons are a bit smaller as they were specifically made to fit these jugs and the replacement was made to fit the steel lined type of cylinders.

Can a machine shop take it down slightly? or any other method?

Thanks,

Chris

73 911 E

[AlfonsoR]

I would give them (JE) a call and see what they recommend. Just because they have the same casting number, doesn't mean that the final machining is the same. Maybe it is, maybe it's not. They can tell you. And let them know what you're trying to do. They'll tell you if you can or can't and if you can, they might give you input on what's the best way.