Compression

[T jones]

my boat at a shop and the mechanic said that the motor has low compression 1=60 PSI 2,3,4,5 has 110 and number 6 has 90 does this mean that the motor is shot or can it be Decarb to get more compression the motor has been sitting up quite awhile.:laugh:

 

[Scott Danforth]

Welcome aboard.

you posted in the prop questions forum. what kind of motor? could be needing a decarb, probably needs rings or some other item replaced. will flag this for a mod to move.

 

[alldodge]

my boat at a shop and the mechanic said that the motor has low compression 1=60 PSI 2,3,4,5 has 110 and number 6 has 90 does this mean that the motor is shot or can it be Decarb to get more compression the motor has been sitting up quite awhile.:laugh:

:welcome: to iboats

If it sat long enough it could have some rust on the cylinder walls which could have damaged the rings. As Scott mentioned we could use some more info on what engine, how long it sat, what was done when you went to restart?

 

[Frank Acampora]

Doesn't matter what the engine brand is or what size it is. Compression ratio will tell you a lot.

If it is a 2 cycle outboard: Usually, if an engine needs reboring the compression will be 20 or less. Your engine may need something as simple as a head gasket. At 60 PSI, it is also possible that a top ring has broken and only the second ring is holding compression.. NOW: if your engine is a Merc "Tower of Power", replacing a ring requires complete disassembly because Mercs do not have separate heads. Some OMC engines are like this also.

 

[WIMUSKY]

Welcome to the forum, T jones. When testing compression, the first thing you look at is consistency across all the cylinders, 10-15% of eachother tops. #1 is in rough shape. Could be a head gasket, but your other numbers are low too. I'm assuming you have an I/O since your Topic landed in that section. May have to clean up the cylinders and re-ring it....