Alex29573 Posted August 4, 2009 Report Posted August 4, 2009 I got a banshee that had 30 psi in both cylinders, so i got the cylinders honed and put new rings on the pistons. I put it back together with all new gaskets and it has 40 psi now.. Can bad reeds cause low compression? what else? Quote
quikshee Posted August 4, 2009 Report Posted August 4, 2009 You may have needed a bore, not just a hone and rings. It sounds like the new rings seated a bit tighter than the old ones, hence the 10lb jump in compression. Did you have the cylinders measured before and after the hone??? Just an idea. Quote
TwistedSheeRida Posted August 4, 2009 Report Posted August 4, 2009 i bet your cylinder is out of round have you checked for air leaks Quote
spurdy Posted August 4, 2009 Report Posted August 4, 2009 You may have needed a bore, not just a hone and rings. It sounds like the new rings seated a bit tighter than the old ones, hence the 10lb jump in compression. Did you have the cylinders measured before and after the hone??? Just an idea. If you just checked the compression after replacing the new rings and not breaking the motor in then the new rings are not seated yet. I would bet that the cylinder is out of round or you have a leak between the head and the cylinders or a leak around the spark plugs. You are compressing the air from the closing of the exhaust port into the cylinder and into the head. Any leak from that point will cause a low reading. Reeds don't play a part in this. SP Quote
black sunshine Posted August 4, 2009 Report Posted August 4, 2009 (edited) Your shitty compression tester. Cross reference with another one. How many kicks to start it? How are you performing the test? (your not just kicking it once, are you?) Edited August 4, 2009 by black sunshine Quote
T_Shee Posted August 5, 2009 Report Posted August 5, 2009 ya make sure you kick it until the needle quits climbing with wide open throttle Quote
Wildcardracing Posted August 5, 2009 Report Posted August 5, 2009 I suspect you weren't holding the throttle wide open or didn't kick it till the needle stopped moving. But several things can cause a decrease in compression: Worn, broken or damaged piston rings Over sized,damaged or out of round bore glazed cylinder walls Damaged piston and yes broken or non sealing reeds Quote
spurdy Posted August 5, 2009 Report Posted August 5, 2009 I suspect you weren't holding the throttle wide open or didn't kick it till the needle stopped moving. But several things can cause a decrease in compression: Worn, broken or damaged piston rings Over sized,damaged or out of round bore glazed cylinder walls Damaged piston and yes broken or non sealing reeds How would reeds effect compression testing? The intake feeds the crankcase and the flow is through the transfers into the cylinder. Then as the piston comes up and traps the volume in the cylinder once the exhaust port roof is closed is when the compression starts. Correct me if I misunderstand the concept, but I don't see how the reeds would effect it. Even if the reeds were removed, once the intake was closed as the piston traveled down the pressure increase in the crankcase would force the charge up through the transfers into the cylinders. SP Quote
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