Compression on 85' 140 VRO

[Sal G]

A spark plug "steamed cleaned" led me to believe that my bogging down problems were related to water entering my top right cylinder. Upon removing the head gasket there was an area that looked scored-<br />also some score marks on the top of the piston head- almost if the spark was arching (did have an electrical problem with a dual battery system last year). Compression on 3 of the 4 cylinders ran approx. 135-140psi. The "steamed" cylinder only showed 60 psi but immediately jumped to 80 psi<br />as soon as we replaced the gasket. These readings<br />were taken with the engine cold- something I now realize was done wrong (live and learn by reading some great stuff in this forum)<br />Anyway to make a long story short (or shorter)-<br />the boat now literally runs fantastic. Reaches<br />about 6200 rpms at WOT. Somewhat baffled because<br />there is such a large difference in compression in that one cylinder but the engine idles fine and<br />and is smooth. The engine does have a very slight <br />"clanking" noise when idling. Is this normal for a 2 cycle engine? What does crossflow mean. Is this engine a crossflow? What do you pros out there gather about this compression thing? What is the "normal" compression and max WOT for an 85 140HP engine.Just trying to keep what I have in the best possible condition. I do own a Clymers manual but I'm more of a visual person and I don't understand <br />alot what is said in the book. Thank you to all who have been so informative.

 

[Sal G]

Re: Compression on 85' 140 VRO

Cylinder damaged because of water?

 

[wilde1j]

Re: Compression on 85' 140 VRO

I have an '85 140 and compression is generally in the 150 to 160 psig range. The low cylinder you have (~ 80 psig) is too low (10 to 15 psig delta is acceptable) and indicates that cylinder has a problem.<br /><br />Your motor is not a crossflow, but loop charged. Search here to find a good explanation of the difference.<br /><br />I would be inclined to remove the head on the bank with the low cylinder. Look for signs of head gasket leakage. The "steam cleaned" plug indicates you have water getting in that cylinder (not good).<br /><br />If you don't find any obvious problem (cracked block/sleeve, head gasket leak or other block abnormality) reasemble using a new head gasket, install dry and torque to proper value. Retorque after ~ 10 hours running time.<br /><br />You clearly have a problem that needs to be found. Good luck.