ninjette.org - View Single Post - Low Compression On A Cyclinder, Should I Replace Piston Rings?

nocturncal · February 8th, 2020, 09:12 PM

I did the leak down test and got some results I don't quite understand.

With the leakdown regulator set at 100 psi, the cylinder pressures I got were:

Cylinder #1: 99 psi
Cylinder #2: 99 psi

No air leak from intake, exhaust, or radiator cap.
Air only coming out through oil filler cap, both cylinders tested had this problem.

I rechecked compression and got:
Cylinder #1: 155 psi
Cylinder #2: 160 psi.

Cylinder #2 was the cylinder which was originally testing at 110 psi. I'm guessing after I did a wet compression test described in my first post, even though I ran the bike to blow out the excess oil for 45 min, that maybe some oil is still there helping the piston rings seal and that's giving me my better numbers?

I also was kinda confused about trying to find TDC on cylinders when I didn't have the valve cover off to see the camshaft lobes, so I ended up trying both cycles of 1T and 2T and chose the one didn't have air blowing through the intake.

My carbs are in a land far far away right now being cleaned, so I can't run the bike

February 8th, 2020, 09:12 PM	#6
nocturncal ninjette.org member Name: Cal Location: San Francisco Join Date: Jun 2017 Motorcycle(s): '09 Ninja 250R Posts: 180	I did the leak down test and got some results I don't quite understand. With the leakdown regulator set at 100 psi, the cylinder pressures I got were: Cylinder #1: 99 psi Cylinder #2: 99 psi No air leak from intake, exhaust, or radiator cap. Air only coming out through oil filler cap, both cylinders tested had this problem. I rechecked compression and got: Cylinder #1: 155 psi Cylinder #2: 160 psi. Cylinder #2 was the cylinder which was originally testing at 110 psi. I'm guessing after I did a wet compression test described in my first post, even though I ran the bike to blow out the excess oil for 45 min, that maybe some oil is still there helping the piston rings seal and that's giving me my better numbers? I also was kinda confused about trying to find TDC on cylinders when I didn't have the valve cover off to see the camshaft lobes, so I ended up trying both cycles of 1T and 2T and chose the one didn't have air blowing through the intake. My carbs are in a land far far away right now being cleaned, so I can't run the bike Last futzed with by nocturncal; February 9th, 2020 at 12:46 AM.