My 1996 John Deere 425 with the 20 HP K-Series engine Model FD620D has a lot of oil blow by coming from the oil fill. It is so bad that will blow the rubber fill cap off the fill tube. There isn't any exhaust smoke so I am wondering what causing this. If I have to pull the engine and overhaul it what is the approximate cost for parts and labor. Thank you.
Excessine crankcase pressure without oil smoke from the exhaust generally means a blocked engine breather.
The cost will be about $ 6.00 for a new breather gasket and about 1 to 1.5 hours of labour so it is a do it yourself job.
You can verify the blocked breather by removing the breather tube from the engine and running it for a short time ( it will be very messy ).
If there blowing from the dipstick tube is a lot stronger than the blowing from the breather tube then the breather is blocked.
the JD web sie has your service manual available on line for free, but you can only view a small section at any one time.
Or you can buy a copy. They are not cheap but excellent value as they are written for owners with almost no machanical knowledge so easy to follow and fool proof.