ST-120 Oil Leak

mharrison

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Just inherited a 1989 Bolens ST-120. I was told the crank case seal has been replaced in the past and apparently has blown again as it is leaking oil out of the bottom of the engine. I would think that it would blow due to crank case pressure but I am at a loss as to what could be causing that. My son and I want to try to fix it ourselves, but I'm not against just taking it to a shop if need be, or even just replacing the motor.

Any thoughts on what could be the cause and what I could possibly do to resolve it?

I've only ever worked on my Cub Cadet RTZL54 so this one is a bit new. I'd like to get it working as it was eventually passed down to me and my son and it was my grandfathers first riding lawn mower and the one I learned to mow with, so it has some sentimental value to my family.
 

ILENGINE

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Could be related to a groove worn into the crankshaft where the seals runs or maybe some wear on the lower sump bearing allowing the crankshaft to shift allowing oil bypass. Something else to check and would be more common is the sump gasket is leaking and running underneath.
 

Mower King

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Is the seal still intact and leaking oil past it or, has the lip seal itself blown out of the sump case?
 

mharrison

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I have been checking and I do think it is the sump gasket that is bad. The problem I have now is I cannot find the model number on that 12hp B&S motor. Any chance someone knows the model number Bolens used in 1989 so I can do a lookup on the gasket and oil seal so I can get them replaced?
 

slomo

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Might of installed the new seal dry. Supposed to oil the seal before sledgehammering/jack-hammering it in.

Should be some engine numbers on the engine some place. Briggs website has some locations to check for on it.

slomo
 

gainestruk

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Look on back of the blower housing above spark plug, at that time the etched it into the metal housing.
 

gainestruk

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When you put new seal in leave it a little higher or a little lower than old seal, if there is a grove in the engine where seal goes that will give better seal.
Warning don't drive in too deep I've had piston rod rub against new seal, when you get it in take out spark plug and make sure it turns freely and no rubbing sound or feeling really tight, do this with old seal before you take it out so you know how it feels, new seal will feel a little tighter than old one.
 
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