New rings = less power :(

[Aero Fifty]

Subject says it all.. I took the top end off to investigate a noise, broke a ring putting it back together so I replaced the top end with all new honda parts. Now its down on power and lost about 10-15 mph. What did I do wrong?
Oh the compression is a tad above 90psi the same as my other 40+mph aero.

[Lunytune]

How much did you replace? Cylinder too, or just rings and gaskets? If you did not replace cylinder, did you hone the old one? If not, rings will not seat and seal properly. I think your compression should be higher than 90psi for a rebuild.

Then again, your problem may be from another cause and coincidental to the rebuild.

[Kenny_McCormic]

You never rebuild an engine unless it needs it.

[Aero Fifty]

I did have the cylinder honed and the only part I reused was the piston. Basically I took it apart to diagnose a noise which turned out to be excessive carbon buildup on the top of the piston. After I cleaned it up I put on new rings, bearing, and seals. Now the noise is gone but the power is down.
Maybe I just need to break in the new rings?

[tru72]

90.. dam im surprised it still starts!
anything close to 100 i recommend to customers to change rings or even replace bore. Like i said in a previous post. 120 your still surviving! lol
sounds like your cylinder is worn out already, did you check the measurements before replacing the rings?
aloha
D

[Aero Fifty]

Well it was running fine before I broke the ring when I took it apart to investigate a rattle. Which turned out to be excessive carbon buildup on the piston. I took the cylinder to honda and had it honed. They said it looked good? Well I guess i need a new bore now... Could I have screwed up something when I replaced the rings?

[bradthreee]

Did you torque down the head bolts properly?

[Aero Fifty]

To be honest I don't have a torque wrench but I did tighten them up good. Maybe honda took off too much material when they honed it? Ugh this is depressing after I spent $50 on a tiny bag of parts from honda and I can't even get above 20-25mph now.

[Kenny_McCormic]

Honing doesn't take anything worth mentioning off, it just scratches it up, measure ring end gap. use is what wears em out.

[Lunytune]

Sounds like you did everything right. 90psi compression may be best you will get until the rings are seated through break-in. Squirt a dab of 2-cycle oil in the spark plug hole and spin it over a few times to spread the oil. Put plug back in, and give it a shot of starter fluid as you crank. Sometimes that works to get that initial start. Then after a warmup and short breakin, rings should do better and compression should come up.

Primary issue on torquing the bolts is to make sure they are even. I usually do a crisscross procedure, and then after running the engine a few minutes, retorque. Purpose of torque wrench is just to make sure bolts are tight enough without twisting off. If you have a good feel for it, a torque wrench is not an absolute necessity.

[jstone]

Did you get the regular rings or the oversized ones? Actually I'm not sure if there are oversized ring sets, maybe its just pistons. But that wouldn't make much sense either... I would say measure the ring gap and compare it to the service manual and go from there.

[AeroFifty]

Ok so I measured the end gap and its around 0.40mm for both rings. This seems to be within the service limit. I had the wider ring on the bottom piston groove and the thinner one on the top is this correct for an Aero? I just read in another post that the fatter ring should be on top? Which is it??

[AeroFifty]

So lets say I had a rings installed upside down? Would that cause the low compression?
When I put a little 2 stroke oil in the cylinder my compression shot from 90psi to 120.

[Arnadanoob]

Upside down piston rings in some engines won't seal properly.

[AeroFifty]

Well I reversed the rings and reassembled the engine. Initial thought was it was fixed but i hit the first hill and my speed dropped to 15mph and no power. I need to recheck the compression again and make sure the carb is clean. Maybe check the reeds.