New piston/rings or just oversized rings on the old piston.

f4radar

Well-Known Member
#1
I’m confused. Can you just put .10 over rings on a standard sized piston. Or how about .20s or 30s there must be some rules about this that I don’t know about.
 

f4radar

Well-Known Member
#3
Say for a TEC HS50. I get the sizing the ring to the cylinder. I'm just wondering if you use .10 or .20 over rings to get within specs, can you just stick those oversized rings on your standard size piston? or do you need to use an oversized piston?
 
#4
I get the sizing the ring to the cylinder. I'm just wondering if you use .10 or .20 over rings to get within specs, can you just stick those oversized rings on your standard size piston? or do you need to use an oversized piston?
I've used .010 over rings many times to get proper gap, and used them on standard pistons. Worked well. As for .020, never have went that far...
 
#7
We used to knurl the piston skirt on standard pistons on cars when using oversized rings , to keep the piston from rocking. if you have to much gap between your piston and cylinder wall the piston will rock back and forth cutting a crescent in the cylinder wall with the rings. I had that happen on a Harley Shovelhead that I bought from a friend with a brand new bore job & rings in it, 50 miles after the build I had to tear it down and take it back th the shop that did the bore job, he looked at it and asked "what a mess, who did that bore job" should have seen him squirm when it handed him his receipt, wanted to just redo the bore job and me buy the new pistons, NOT!
 

cfh

Well-Known Member
#8
i rebuild a lot of Tecumseh hs50 engines... probably done at least 50 of them for my bikes. and i always buy .010 or .020 oversize rings on the standard piston, and just adjust the ring end gap to the motor in question. i have never used standard rings. The advertised suggested ring gap should be .006 to .020. If you use standard rings, even on a low hours motor, at best you'll end up at .015 ring gap. heck i've bought brand new short blocks and have measured the ring gap and it's never less than .015, and sometimes .020. If you want that tight ring gap you have to buy oversized rings and adjust them to the desired gap. Personally i like .008 to .010. That's what i shoot for.

But the big problem these days is getting oversized hs50 (or hs40) rings. They are just not available. Also with hs50 motors, there's another complication... in the 1990s they changed the bore size slightly when they went to thin rings. So you have to match that up too. Meaning you can't put a thin ring hs50 piston and rings into a thick ring block (or vice versa.) So it's not just a matter of getting hs50 .010 or .020 over rings... you have to get the right style rings too (be it thin or thick.)
 
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