520 oil problems

[kens clidlesdales 0]

Hello there all you fellow wheel horse owners. I have 3 my self. 520-H, 418-A and the one I've own since 1994 the 312-8 .The 520 and the 418 I am restoring. I am having A problem with the 520 I mowed with it for the first time this week and it fouled a plug pulled the air cleaned off and there was oil on the inside of the air cleaner  so I replaced the spring in the valve cover that holds the reed valve in place and the filter but the problem is still there. it seems that the crank case is under pressure. Do you have any idea what could be the problem? thanks

[lynnmor 6,762]

You can check the breather that expels into the air cleaner housing, but they rarely cause problems.  Check the compression, it sounds like a lot of blow by.  Possible causes are bad rings, bad piston or bad valve guide.

[kens clidlesdales 0]

I was thinking  compression as well. Is there normally pressure in the crank case?

[kens clidlesdales 0]

Would you know what the compression should be?

[buckrancher 2,672]

I believe good is between 80lbs - 125lbs crank with the throttle open

[kens clidlesdales 0]

Thanks much I'll check that next 

[lynnmor 6,762]

80 psi supposedly is OK, but I like to see over 100.  Just a minor valve leakage can cause under 80 psi, so if you find that, the head needs to come off to find the issue.  A pressure that is too high usually means that there is too much carbon buildup.

 

There is quite a bit of pressure pulsing in the crankcase.  A serious combustion chamber leak to the crankcase will cause an abnormal high pressure and can push oil and mist laden gases into the air filter.

[kens clidlesdales 0]

Thanks lynnmor for your advise. we will check the compression and go from there but my guess is that the engine has to come apart.