need an engine guru!!!

[oonighttrain]

bought a boat yesterday knowing it had an engine problem.. its a 1997 yamaha 50 hp 4 stroke, overhead cam 4 cylinder that runs ok but, has very low compression on cylinder #1 (like 30 p.s.i)and slightly low compression on cylinder #4. (around 90) 2 and 3 are over 120 psi....
i removed the head to take a peek and do not see any damage whatsoever on the cylinder walls. i took the head to a machine shop so they can do
a vacuum test on each valve.

anyone have any comments or hints for me???

 

[Estevahn]

Sorry,, I haven't got any advice or ideas. But I have a question about that motor, if you don't mind. Does it have rocker arm valve train or lifter bucket?

 

[oonighttrain]

i dont know what a lifter bucket is..

i think the answer is its a rocker arm valve train..

its an overhead cam with no lifters or push rods..

 

[EastcapeAngler]

..When's yer next trip to west train?? Chuck Sperry & Darrin Hauck have a machine shop next to polaris west & they are frikin geniuses! (IF Chuck is still wrenchin') Jim Burton at the cat shop's pretty sharp also.

 

[Estevahn]

with a lifter bucket type, the cam will be directly over the valve.
All their bike engines are that way.. Im just curious if that's what the marine engines have.

 

[ice auger]

four strokes are so nice and quiet, but what a pain in the a$$ to work on...

 

[oonighttrain]

..When's yer next trip to west train?? Chuck Sperry & Darrin Hauck have a machine shop next to polaris west & they are frikin geniuses! (IF Chuck is still wrenchin') Jim Burton at the cat shop's pretty sharp also.

hmm... maybe early march or so.. im hoping...

would be a bit tough for me to bring an outboard head with though...


estevahn, its a single overhead cam with the rockers running on the cam..

i think you are referring to a dual overhead cam...

 

[EastcapeAngler]

hmm... maybe early march or so.. im hoping...

would be a bit tough for me to bring an outboard head with though...


estevahn, its a single overhead cam with the rockers running on the cam..

i think you are referring to a dual overhead cam...

..I thought about that after I posted...Silly me

 

[Estevahn]

estevahn, its a single overhead cam with the rockers running on the cam..

i think you are referring to a dual overhead cam...

Yup,, bingo.. Thanks.