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40 hp Mariner rebuild

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paulc057

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"To make a long story short I

"To make a long story short I am new to the boating community and just recently bought a used boat, after bringing the boat in for a tune up i learned that i had bad compression 100,55,120,120. the motor is a 1996 mariner tracker 40hp to save money myself and my father in law are doing the rebuild our selves. I am trying to trouble shoot to find the cause of the bad compression. after taking the motor apart the cylnder which was at 55 psi was extremely discolored and the rings were shot. the other cylnders had some wear on then which would have eventually went bad. does anyone have any idea as to what may have caused this....aslo the engine is oli injected, does anyone know if it is a good idea to disable the oil injection and start mixing gas. thank you for your time this is a great site. also if anyone has any tips or tricks while doing the rebuild please let me know."
 
Usually blocked carbies play a

Usually blocked carbies play a big part in ring wear and destruction so give them a good clean out befor you crank the engine up
 
"Agree, the oil injection work

"Agree, the oil injection works fine on these and it's a simple, factory set, 50:1 constant rate pump.

Oilers get blamed for everything from an overheat to a busted prop - they almost "never" are the fault.

If the oiler went you would have 4 cylinders with 50 psi...

I would leave it there, if for no other reason than you will have something to blame should you ever neglect the motor and develop a problem - then YOU can say "damn oil injection" and everyone at the boat ramp will nod


Seriously though, the oil system is decent. If you will sleep better at night ripping it out, then do it for the peace of mind. Otherwise, keep it topped up and let it do it's job.

Dirty/old unstablized gas, lack of proper storage and the resuting blocked jets in a carb are probably the main cause of the damage to that powerhead, with a contribution from the maybe original (or maybe changed once) impeller."
 
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