Crankcase seals/gaskets

RandyJ

RandyJ

Master Chief Petty Officer
Joined
Jun 13, 2002
Messages
808
One marina nearby is a bit notorious for telling people they have a leaking crankcase seal/gasket. Out of curiousity... how would this be diagnosed? What would be the symptoms? (I've got a waverunner and an old 65 hp Mercury that I suspect this problem)...
 
Faztbullet

Faztbullet

Supreme Mariner
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Mar 2, 2008
Messages
15,619
Re: Crankcase seals/gaskets

The old mid 70's Johnrude 50 was bad about this, sign are: idles ok out of gear but dies in a few seconds when in gear, primary timing advanced futher than normal, weepage around crankcase halves, lean spits that cannot be corrected by jetting and sometime weak fuel pressure allow carb/s to run lean at idle.
 
RandyJ

RandyJ

Master Chief Petty Officer
Joined
Jun 13, 2002
Messages
808
Re: Crankcase seals/gaskets

I've got a 1990 Yamaha 650 waverunner that idles fine. It won't rev up. I can completely close off the carburetor intake and there is no change while running. Just wondering if that would be a crankcase or shaft seal allowing it to suck air from the wrong place??? I've also got an old (circa 1970's) Mercury 65 hp that simply will not rev no matter what I do.... new plugs, carbs cleaned and even replaced... kinda leaning toward a high speed coil or something like that but don't know how to diagnose that problem.
 
Faztbullet

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,619
Re: Crankcase seals/gaskets

On the ski it may be the rear seal as these are the ones that wear on the 650 and also check the reed block as these are known to crack causing acceleration problems but check/clean the carb as it may need new diaphram in it. The 65 idf a older 70's should have the distributer thus no high speed coil......
 
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