A co-worker recently rebuilt his Tecumseh 8hp snowblower engine. He went to a local small engine shop to order the parts. They told him that a .010-over piston is not available, and the official recommendation is to use a .010-over ring set on the standard piston. He had it bored .010-over and installed the parts supplied by the shop. He said it seems to run fine, but is uneasy about the piston. It sure doesn't sound right to me, either, but I'm sure not a small engine expert. Can anyone shed some light on this? Thanks.
Tecumseh oversize piston
- Thread starter zrxkawboy
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Wow! It must sound like the piston is ready to come out
What else can he do? With no oversize piston available it's either replace the engine or try the oversize rings. Even if the piston rocks back and forth, makes noise, and wears out a little faster it's no big deal, he'll just have to replace the engine.
There are a couple of things that could have been done that would have resulted in a better outcome.
If the bore was not scored to the point of needing a rebore, it could have been just honed and then the .010 over rings gaped to the proper specification. This would have helped maintain closer piston-bore clearance.
The piston could have been knurled to restore the proper piston-bore clearance in the .010 over bore. Knurling could have been applied in the case of honing also.
Ed
If the bore was not scored to the point of needing a rebore, it could have been just honed and then the .010 over rings gaped to the proper specification. This would have helped maintain closer piston-bore clearance.
The piston could have been knurled to restore the proper piston-bore clearance in the .010 over bore. Knurling could have been applied in the case of honing also.
Ed
Back in the day, it was common to get a piston skirt Knurled to solve a problem like this,
http://en.wikipedia.org/wiki/Knurling
"Knurling may also be used as a repair method: because a rolled-in knurled surface has raised-up areas surrounding the depressed areas, these raised areas can make up for wear on the part. In the days when labor was cheap and parts expensive, this repair method was feasible on pistons of internal combustion engines, where the skirt of a worn piston was expanded back to the nominal size using a knurling process. As auto parts have become less expensive, knurling has become less prevalent than it once was"
In your application I'm sure it would work well.
http://en.wikipedia.org/wiki/Knurling
"Knurling may also be used as a repair method: because a rolled-in knurled surface has raised-up areas surrounding the depressed areas, these raised areas can make up for wear on the part. In the days when labor was cheap and parts expensive, this repair method was feasible on pistons of internal combustion engines, where the skirt of a worn piston was expanded back to the nominal size using a knurling process. As auto parts have become less expensive, knurling has become less prevalent than it once was"
In your application I'm sure it would work well.
It's too late now but I would have just put in a new set of std rings and went on with it, I do not see any benefit to oversizing bore and using bigger rings with a std piston other than a way to sell off .010 ring sets.
Must sound like a piston slapping chevy.
ken
ken
Originally Posted By: JR
Must sound like a piston slapping chevy.
ken
I was thinking this too!
Must sound like a piston slapping chevy.
ken
I was thinking this too!
It's only .010 over. Many small engines wear themselves that much (and more) just in normal operation over time. No, this isn't the ideal situation, but at least the ring gap and tension is what it should be. Now it was .030 over with a standard size piston, I'd say no way.
You friend says it seems to run fine and I'm sure it does. Maybe that small engine shop knows what it's talking about.
You friend says it seems to run fine and I'm sure it does. Maybe that small engine shop knows what it's talking about.
^^^ I was going to say the same thing.
In my old chevy we had to bore it to 040 bc the cylinder walls were worn that far. The ridge land at the top was huge, where it was never worn. So the whole cylinder was opened up to above .030, with the original pistons doing their thing all day long. It didn't make a sound.
In my old chevy we had to bore it to 040 bc the cylinder walls were worn that far. The ridge land at the top was huge, where it was never worn. So the whole cylinder was opened up to above .030, with the original pistons doing their thing all day long. It didn't make a sound.
Most cyls need to be bored to make them round . Worn cyls are never round , usually an oval shape of sorts . Putting new round rings in an out of round cyl will never wear in proper .
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