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Rex L.
Rex L., Small Engine Technician
Category: Small Engine
Satisfied Customers: 761
Experience:  auto-diesel graduate. small engine and John deere and silver certified in stihl.
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Oil cap is blowing off john deere 425 tractor. Is it pvc valve

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Oil cap is blowing off john deere 425 tractor. Is it pvc valve or crank case breather clogged and how do you get to these parts to check. Where are they?
Hi, My name isXXXXX you for letting me try and assist you with your problem.
That sounds like a crankcase breather There's a hose inbetween the cylinders that comes out of the block. You can check to see if it's clear.
Customer: replied 5 years ago.
Tell me where does the hose connect on each end. You said it comes out of block, it where does it go to from there
It should come up to the airbox.
Customer: replied 5 years ago.
I checked that small hose. It is clear. ANy other ideas?
Customer: replied 5 years ago.
Relist: Incomplete answer.
Make sure you have a clean air filter. This system will not work correctly if the air filter is getting dirty or plugged up.You could also have a head gasket that is bad and letting compression into the crankcase. You can check a compression with a compression tester and the cylinders should check about equal. (140 to 170 psi). Also the dipstick should fit snug when pushed in and do loosen up over time and may need a new one. Check air filter first.
Customer: replied 5 years ago.
Hi,
Will check your suggestions out. Thank you. I want to give you a little more info about this engine. It is a Kawasaki 20 HP gas engine used in John Deere 425 lawn and garden tractor. I use a 54" mowing deck. I have heard that this problem can be caused by plugged pvc valve but don't know where this is located. Do you know anything about that. Also, I am getting positive pressure from dip stick tube. Shouldn't it be negative or slight suction from it? Let me know what you think. I will first change out air filter to see if that helps.
Bill
The pvc valve i believe on your model is in the crankcase vent that you have already check. A normal would be positive and negative pressure as the pistons go up and down. Usually you will have more positive as the engine gets worn. You will get more positive pressure if the rings are getting bad or head gasket blown. I would rather you run compression test on engine before you have head gaskets changed . They may be fine.
Customer: replied 5 years ago.
OK, one more question. If pressure test is low, what does that mean and what repair does that signify, especially if only one is low and how low from normal signals a need for repair. I have fairly constant positive pressure from dip stick tube, you are saying that's to be expected from old engine. No smoke from exhaust when running, so rings may be okay. I do get some oil build up around carburetor. Does that signal anything. Thanks for your prompt replay
Bill

If pressure is low it can be rings. Or you have a valve not seating correctly. If a valve is not sealing correctly it will allow compression bypass but it will put the compression in the intake or exhaust. If you have a cylinder testing low on compression spray some penetrating oil in spark plug hole and test again. If compression is much higher the rings are worn. (The oil seals the rings). You can also have a leak down test done and it will test the rings and valves at the same time. It requires a leak down test that a good shop will have but are kinda expensive.

Rex L., Small Engine Technician
Category: Small Engine
Satisfied Customers: 761
Experience: auto-diesel graduate. small engine and John deere and silver certified in stihl.
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