Piston condition?

[PiratePast40]

There are a few blemishes on these pistons and wondering if they are OK to use. Both have these small amounts of what looks like little bubbles from displaced material on the side of the piston above the upper ring groove. You can feel it with a fingernail on one of them but not on the other. There are similar marks on the tops of the pistons but you can't feel them with your fingernail.


I'm guessing these are from detonation but it really doesn't matter at this point. There do not appear to be any other rub marks, cracks, discoloration, melting, or anything else that I can see that would indicate a problem.

I realize this is subjective but don't have experience in this area. Thanks for any help.

 

[Don S]

Re: Piston condition?

I would say it's probably from rust & corrosion from setting with moisture causing rust in the cylinder, more than detonation. I would suspect detonation to start from the top of the piston and work down to the ring, your defects start at the ring and decrease toward the top of the piston.

 

[jerryjerry05]

Re: Piston condition?

Try cleaning them up with a wire wheel.Bumps and pits will allow carbon build up and eventually possible failure.They might last another 35 years or 1 year.
I'd use them.J

 

[Don S]

Re: Piston condition?

Try cleaning them up with a wire wheel.Bumps and pits will allow carbon build up and eventually possible failure.

I don't think I would try to smooth them out with a wire wheel, or you will have a bunch of low spots. Personally, I would use them just the way they are. Carbon build up is seldom a problem on a boat that is actually run normally. More likely to be found on ones that are used for trolling all day, day in and day out.

 

[sschefer]

Re: Piston condition?

There's a couple of things you need to do before you re-use a piston. You need to check them for skirt clearance and out of round. There are acceptable amounts for both and the numbers can usually be found in the Shop Manual.

Most pistons (even new) will be slightly out of round so once you check them you need to run a bore gauge down the cylinder and check it for being within spec for both size and round.

It that all checks out then you can feel fairly safe that you won't cold seize it or scuff them up during the break-in.

If you don't have the tools for checking these things you can usually take them to a shop and have it done. I've never been charged for it but I do a lot of business with the shop I deal with.

Those pistons look really good compared to some that I've seen. If they check out, I'd re-use them.

 

[PiratePast40]

Re: Piston condition?

I've checked the bores for out of round and diameter. They're in great shape. I'll go ahead and check the pistons as well. I suspect (but don't know yet) that the pistons aren't too out of round because there aren't any scuff marks on the skirts or on the cylinders. But you're right, there's no way to know for sure unless you measure. I was concerned about getting too agressive with a wire brush on the ring grooves and lands but hadn't even thought of taking off so much material that they would be out of round.

Thanks for the heads up on everything!