Can you replace just one piston?
Yes, you can replace one piston, but if you don’t pull the engine down and have it balanced to the rest of the rotating assembly, it technically could be out of balance. If you buy the exact same piston you probably won’t notice it.
Can you reuse pistons on a rebuild?
Reusing the original pistons is no problem, as long as the piston skirts and cylinder walls are in good condition. The cylinders need to be measured very carefully, as they wear unevenly and a hone may not clean them up. As far as replacing just one piston, that is OK too – again with some precautions.
Do pistons have to go back in the same cylinder?
Unless the cylinders have been honed to fit each individual piston, you should be able to swap them freely. Technically, the rods don’t have to go back on in any particular order. They do have to be correctly oriented. “Smooth side” facing each other and “beveled side” facing away from each other.
When to reuse pistons or order new ones?
If either the piston or the top ring exhibit evidence of micro-welding, the only solution is a new set of pistons and rings. Avoiding a re-occurrence of this issue involves careful initial ring break-in that allows establishing early wear patterns that remove the tallest peaks early before maximum cylinder pressure is applied.
What happens when the rings are removed from a piston?
When the rings are removed from the piston, evidence of micro-welding will be pitting in the lower surface of the ring groove and the lower horizontal face of the ring itself. This will be more prevalent with pistons that place the top ring closer to the piston crown as this increases the temperature the ring must face.
How can you tell if a used piston is still working?
One of the first things to check on a used piston is that the ring groove clearance is still within spec. Install the ring in the groove and use a feeler gauge to measure the clearance. Beyond worn ring grooves, high output engines and especially supercharged or turbocharged engines tend to load the top ring with far more cylinder pressure.
What should the clearance be on a Pistons?
Although axial clearance recommendations will vary with specific pistons (and manufacturer), a generic clearance of 0.001 to 0.002″ is acceptable. This can be measured with a feeler gauge between the top of the ring and the groove.