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I just pulled apart my old LawnBoy 2-cycle mower engine. The needle bearings had come loose and were scattered inside the engine. Not too much visible damage, except...

Here's my problem: One of the needle bearings punched into the edge of the piston on the combustion side. It broke the piston ring and wedged into the piston. So, the leading edge of the piston has a needle-bearing-sized notch in it, on the edge. The notch is about 1/16" wide and extends down the side of the piston about 1/2" (i.e., exactly the size of the needle bearing.

The notch extends through the two other ring-type things on the side of the piston (not sure what these are called).

There is no visible damage to the cylinder block.

Here's my question: Will a repair be sufficient if I just replace the piston ring, or would I need to replace the piston? If I have to replace the piston, I might just chuck the whole thing and start over with a new mower (this mower is 20 years old).

Any suggestions?

Thanks!

--Carl

I find it hard to believe that if the piston is scored, the cylinder is not. Better look closely.

Yes. I thought the same thing, and looked carefully. The bearing was punched into the side of the piston, but no damage to the cylinder walls.

Still trying to figure out if I need to replace the piston.

For what it's worth, the Lawn Boy model number is 10201, serial #3937735.

Thanks!

--Carl

If the piston is visibly damaged, I'd replace it.

Here's a link to an F-series piston set a from a website that I've dealt with. They also have good prices on things like hones, fuel line, filters, etc.

I think it's common for the piston to be made from much softer metal than the cylinder wall so it's entirely possible that the wall isn't damaged significantly. However, I'd hone it before reassembling.

I have put together engines with banged up pistons and it worked out just fine. Send a picture? Do the rings fit in the groves OK?