what are good numbers and what numbers would it be time to rebuild ?

IMO even across all cyl is more important

You can also listen to where the air is leaking from to determine exhast intake or ring leaks to narrow it down.

I would also do it with the engine at operating temp

a cylinder with 20% leakage needs attention,its true that it may seem to be running fine,but power is being lost,and it will not get better,ie,it wont fix itself.

so if boat is winterized in building that is only 40 should i wait till spring

no,even a cold reading can give you a heads up if you have a serious problem,if you wait until spring,and then find a problem,you will be working on the boat,instead of enjoying it.

1 cyl,,,,or alll 8 ?

I see anywere between 8-15%,w/ not much residue in the puke tank on my blower motor.

Gapless will give ya false reading,but like above if one is out of line,start looking.

all 8 willl be tested

time for some total seal rings,,i see 2 to 4 % on the engines i have done..

Copied this from a blown alky site.

"The only thing I use leakdown for is a comparison to the rest of the cylinders. Not a condition of the motor itself. If you have 20% leakage, I would say that's good, as long as the rest of them are comparable. Gapless rings create their own set of issues. Besides, you don't race with the engine not running. And I guarantee, the rings will seal better with cylinder pressure. Gapless rings have a tendancy of trapping blowby between the top and second ring. When this happens, it unseats the top ring (bad) and you lose ring seal and power. But the leakdown number look great, who cares."


"Forgot something. One time I was told to try something, so I did. I did a compression test with our standard ringset, hellfire dykes top, cast 2nd and 3 piece oil ring. All the plugs out, throttle wide open, gauge read about 200PSI after the 4th pump. Pulled no. 1 piston out, changed the 2nd ring to a gapless ring and put it back together. No other changes, everything was the same. After the 4th pump on the gauge, 145PSI. After advancing the cam a total of 6 degrees, I finally reached 160PSI. I know what your thinking, yes, the ring was put together the right way, it wasn't upside down. Went back to the cast 2nd ring and ran the compression test again. It escapes me now what the gauge read with the cam advanced, but after putting the cam back to where it was, it read 200PSI again. After that, I threw all the gapless rings we had in the shop into the trash."