# John Deere JS45 w Briggs OHV engine



## Spit (Nov 3, 2006)

I picked up this mower. It is one of the caster deck models that were made by Snapper for John Deere. I think that it may be 6-8 years old> I notice that it seems to burn oil..smoke and smell. The spark plug was pretty oil fouled, I cleaned it and when I ran it for 30 minutes or so I had more fouling on the plug.

The oil in it seemed real black, and thin..like watery maybe someone was using too light of an oil.. when I changed it, it was hot so it should be somewhat fluidy.
I put in 30 weight and adjusted the valves to .006 seems to be less smoke. I am wondering what and how I can check for more problems related to it using oil? 

Could I have a ring that is sticking in the groove on the piston and not sealing like it should. I have read about running a mix of gasoline & Techtron fuel cleaner thru 2 cycle engines and cleaning up rings etc. Will this help on a 4 cycle.? The engine is a Briggs 12S502 0114 B1 Serial 08040763B . it is rated as a 8hp. Seems to run good starts in 2 pulls after priming. I did buy an inexpensive Harbor Freight Leak down compression checker..I have never used it. Not sure what would be a good reading..guess I could play around with that and see what I get. 

I'm not sure I want to pull the whole valve asby off to get to the head and cylinder. I have never done that on a OHV. I know on th eL heads you can clean the carbon of of the head and top of the piston with a putty knife 

Any ideas apreciated.


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## paulr44 (Oct 14, 2008)

Stuck ring on a 4-stroke? Don't put money on it.
Can't do compression test on engine like that, as is equipped with a compression release.
Leak-down test, no more than 10%, must hold flywheel/crankshaft steady at TDC on compression stroke to perform test - easier to do with 2 people.

Many reasons it could be smoking - and oil being thin is curious. Does the oil smell like fuel?

Given it's age and my experience, I'd suggest it has a leaking head gasket IF it hasn't been subjected to dirt ingestion (in which case, cylinder/piston ring wear).


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## usmcgrunt (Sep 16, 2007)

I agree with paul (congrats on having past 1000 posts :hat the head gasket is a likely candidate for replacing. It is fairly common for the gasket to blow out between the cylinder wall and valve galley.

You may also have a leaking float or needle valve in the carb allowing gas to enter the crankcase and causing the thin oil.


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## Spit (Nov 3, 2006)

My problem is resolved. Unfortunately the engine threw the connecting rod and blew out the crankcase. I took the engine apart and found a lot of scoring on the bottom of the piston. Previously I found that the oil breather tube had not been connected to the rubber boot not sure if that could have caused excess junk to get into the engine? The breather tube was heavily coated with junk so I think that the boot had ben off for some time. When I first changed the oil it seemed like there was very fine silvery metal in suspension in the oil. 

I tried to adjust the govennor and the spring on the linkage but is seemed to make no difference.

I was having trouble with it surging..and wanting to run too fast. Could the scoring have played a factor in that? If the engine was being loaded up by the extra resistance from the scoring would it cause the engine to race? 

I know that I am not going to be able to fix this engine but I am interested to hear what anybody knows about how an engine with a scored piston might behave. and possible causes of the racing/surging of the engine. I may well run into something similar in the future and would like to know better what to do.

Spit


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## Sir Thomas (Dec 7, 2013)

Spit said:


> My problem is resolved. Unfortunately the engine threw the connecting rod and blew out the crankcase. I took the engine apart and found a lot of scoring on the bottom of the piston. Previously I found that the oil breather tube had not been connected to the rubber boot not sure if that could have caused excess junk to get into the engine? The breather tube was heavily coated with junk so I think that the boot had ben off for some time. When I first changed the oil it seemed like there was very fine silvery metal in suspension in the oil.
> 
> I tried to adjust the govennor and the spring on the linkage but is seemed to make no difference.
> 
> ...


My dad always said when you buy a used car you buy another man's problems. This might apply to yard equipment, especially the larger equipment. There is no telling the neglect the previous owner gave to the mower. The oil in a 4 cycle engine does two things. Keeps frictiion areas lubricated and to keep the engine cooler by reducing friction. 
Low or no oil has a domino effect. Lack of lubrication in the cylinder, which get's hot anyway because of combusion, will cause the piston, rings and rod to overheat and break down. The fouled plugs indicated ring breakdown. I think this series of events had already started before you got it. Whether you could have saved this engine if you had broken it down depends how far down the road the damage began. Could the previous owner have run the wrong weight oil? Possible.


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