1990Onan520-H 15 #1 Posted August 6, 2019 Hey all, just wanted to get some educated opinions on what to do with a couple of my engines on my 520's. Long story short I have 2 P220G's that need work. 1 surges and although I can't find any, I'm assuming it has an intake leak. This particular engine has only 85 psi in each cylinder and has just under 1000 hours. It has never had any valve adjustment or de-carbon done. The second engine is basically the same, but has 1250 hours and 90psi/30psi in its cylinders... also never any maintenance. Are these engine tired and probably just need a rebuild or is there any hope of bringing them back to life by doing a de-carbon/valve adjustment? Share this post Link to post Share on other sites
WHX?? 51,781 #2 Posted August 6, 2019 My guess is some valve seat issues but you never know. I say pull both apart and see if you can get one out of two. Never know might just get lucky and get by with a re-ring or something less $$. I am in the same boat with a 220 that burns oil & fouls plugs but won't know what's going on or worth saving till it comes apart. Share this post Link to post Share on other sites
1990Onan520-H 15 #3 Posted August 6, 2019 1 minute ago, WHX24 said: My guess is some valve seat issues but you never know. I say pull both apart and see if you can get one out of two. Never know might just get lucky and get by with a re-ring or something less $$. I am in the same boat with a 220 that burns oil & fouls plugs but won't know what's going on or worth saving till it comes apart. I've got another p220g with 800 hours that slung a rod, that might have some good parts on it. It did punch a hole through the block though so not sure. The cylinder pressures didn't change much on either engine with oil added so I do agree with valve issues being likely. They did come up some, so it could be a combination of both but probably mostly valves. So you doubt a valve adjustment and de-carbon will bring compression back? I was hoping valves were sticking open a hair or not opening enough hurting compression. Or jammed with carbon and not sealing right. How do I know I have valve issues once I open these guys up? Other than seeing a loose valve seat? Share this post Link to post Share on other sites
Bill D 2,256 #4 Posted August 6, 2019 Make sure you do your compression check with the throttle wide open. There will be a big difference in readings if you don't. If nothing changes open them up and see what you have. From everything I have read on here the P220's are known for valve seat issues. People don't seem to have as much problem with the valves on the P218 and P216. If your interested, I have a P216 with 630 hours I would like to get rid of. It will need governor work. PM me if interested. 1 Share this post Link to post Share on other sites
lynnmor 7,824 #5 Posted August 6, 2019 If you still have some valve clearance, then the valves and seats may need ground. Note that I said ground, not lapped. I don't believe in lapping valves that already have seat contact area that is too wide. I have had that low of compression come back after a valve job. 2 Share this post Link to post Share on other sites
seven 202 #6 Posted August 8, 2019 Take his advice ? I would Share this post Link to post Share on other sites
