zeedubbya 18 #1 Posted May 2, 2013 Last week 520h started spewing gas out of carb again and flooding out under load. Cleaned carb really good twice and nothing. Adjusted valves and it fixed it. I just adjusted the valves last year? What is going on? What would cause them to Get out of adjustment that fast? I'm thinking the seat is getting ready to go, but I hope not! Any suggestions would be appreciated?! Share this post Link to post Share on other sites
MalMac 1,328 #2 Posted May 2, 2013 I think your on to something with the valve seat. If you can't keep valves in adjustment especially on a Onan that would be my guess. If that is what you suspect and I concur I would just go a head and pull the head to verify. Maybe you will catch it in time to save ruining a block. Share this post Link to post Share on other sites
MarkPalmer 80 #3 Posted May 2, 2013 The seat was likely loose to begin with. Adjusting the tappet clearance additionally won't help the matter and can make it worse, so its time to invesigate. -Mark- Share this post Link to post Share on other sites
zeedubbya 18 #4 Posted May 2, 2013 My thinking was if the valves keep pushing down a small amount each time there has to be some sort of change around that seat or on the valve itself. I can't believe the cam is responsible? I imagine the thing needs a decarbon too so it's probably running a bit hot which I'm sure is a recipe for a seat letting go if it isn't already started. I'll probably try and pull the heads sometime next week. Is there anything specific I should look for to indicate a future catastrophy? Share this post Link to post Share on other sites
MarkPalmer 80 #5 Posted May 2, 2013 The valve seats can get excessively hot when the tappet clearances are neglected for a long time, or if the engine isn't getting enough cooling air. The hardened seats will start to press themselves in to the soft aluminum block, then they come loose. If you pull the heads and see problems, don't try to peen the seats in yourself or do any other sort of back-woods repair. I have found most mower shops that are supposed to "specialize" in small engines are clueless when it comes to this problem with these engines, and repairs are best left to automotive engine machine and performance shops, they know how to properly repair the issue. -Mark- Share this post Link to post Share on other sites
W9JAB 156 #6 Posted May 2, 2013 Try adjusting the valves, a little bit on the loose side. Yea you’ll hear them rattle but it dose two things for you. One it will help pound away and build up of carbon and debris on the seat, and two it will pound in a “new†seat of what dose not move. I have used this technique on my Harley with solid lifters for years, and it can extend the time between valve jobs dramatically. Share this post Link to post Share on other sites
woodchuckfarmer 333 #7 Posted May 3, 2013 Get it hot and then take a compression test. That should show you something. It did with mine. Share this post Link to post Share on other sites
