OMC outboard

[mitchjenn]

Dont know if this is the right forum to post this but they look just like a Evin/Johnson. What is the most common reason for cylinder leakage? I have a mid 70s 115 and 140hp OMC that both have above average leakage on all cylinders. Any info would be greatly appreciated.

Thanks.

 

[ezeke]

Re: OMC outboard

Sorry, but I don't understand "leakage". Have you done compression tests and found the cylinders uneven?​

 

[tashasdaddy]

Re: OMC outboard

and give us the model number, so we know what exact engine you have. welcome to iboats.

 

[mitchjenn]

Re: OMC outboard

Well im looking to buy this OMC 115 with an extra 140 power head. The guy says he done a leak down test on the cylinders on both power heads. He says they showed "above average" leakage. I thought maybe the rings or cylinder walls may be worn. Also does anyone know of years and engine horsepower lower units will fit a 1978 Mercury black Max 150hp V6? The only thing i can tell you about the OMC's is that the 115 is between 73' and a 77' model.

Thanks!

 

[mitchjenn]

Re: OMC outboard

He says he did a compression check and it was ok then did the "leak down" test and it was above
average leakage.

Thanks!

 

[tashasdaddy]

Re: OMC outboard

still doesn't tell us anything to go on. sorry, what were the compression numbers? and on what part did he do the leak down test? the lower unit. what's average? post the Merc question in the Merc forum.

 

[iwombat]

Re: OMC outboard

You generally do a leak down test with the piston in different positions. At the very least two - on TDC and one BDC (okay that's a BDC for a four-stroke, I'm guessing two-strokes you'll do the bottom measurement just after the rings close off the ports. Never done one though). That can tell you if your cylinders are getting tapered. A single leak-down number per cylinder won't tell you a whole lot more than the compression numbers.

More data would certainly help us figure out what's going on here. But, generally if the compression numbers are good you should be okay.