rwilson 128 #1 Posted August 13, 2009 I have a 520 H with the onan motor in it. I have recently been having trouble with oil blowing by out of the breather tube into the air filter area. I have replaced the tube and the little flapper that is down in there. And it still does it. Any other sugestions? :thumbs: Share this post Link to post Share on other sites
Gerry w 2 #2 Posted August 14, 2009 Check your governor, it may be broken/out of adjustment causing over revving. Or worse, ring job or valve seats. Share this post Link to post Share on other sites
rwilson 128 #3 Posted August 14, 2009 The tach is broke. So we dont know what the rpm's are. We tried mowing with it at a lower throttle setting and it still did it. The motor was rebuilt 104 hrs ago. Share this post Link to post Share on other sites
kpinnc 14,652 #4 Posted August 14, 2009 The motor was rebuilt 104 hrs ago. Run a compression test on both cylinders. Perhaps a valve is out of adjustment since the rebuild? Kevin Share this post Link to post Share on other sites
VinsRJ 723 #5 Posted August 14, 2009 Question..... Is it smoking out of the exhaust? or it just pushing oil into the airbox? Share this post Link to post Share on other sites
oldandred 15 #6 Posted August 14, 2009 Question..... Is it smoking out of the exhaust? or it just pushing oil into the airbox? hummm he said out of the breather box Share this post Link to post Share on other sites
VinsRJ 723 #7 Posted August 14, 2009 hummm he said out of the breather box Sorry, rwlison stated "blowing by out of the breather tube into the air filter area".... I took that as the air box. I was just asking whether if oil is being passed in both direction. The crank case is being presurized in some fasion, from where I'm not ready to speculate. Usually its the simple things that get you... like is the oil over filled? That can cause blow out into the breather tube. With so little hours and rwilson not indicating a loss of power I would look to the basics first. As suggested a compression test is also a good starting point. I would suggest a leak down test of each cylinder first, right after checking the oil level. Share this post Link to post Share on other sites
rwilson 128 #8 Posted August 14, 2009 It does not smoke out the exhaust at all. No loss of power. It does start hard sometimes. I will check compression. Other than that I have no Idea. :thumbs2: Share this post Link to post Share on other sites
Save Old Iron 1,571 #9 Posted August 16, 2009 Also, the op manual lists the breather assembly as needing maintenance every 200 hours - a clogged check valve can allow the cranksace to develop positive pressure Share this post Link to post Share on other sites
rwilson 128 #10 Posted August 18, 2009 Everything in the picture poster above is brand new. I havn't had time to do a compression test yet but I will soon. Share this post Link to post Share on other sites
Save Old Iron 1,571 #11 Posted September 15, 2009 Did we ever find out the cause for the excessive blow-by ? :scratchead: Share this post Link to post Share on other sites
Tgblanken 27 #12 Posted September 15, 2009 I have a 520 H with the onan motor in it. I have recently been having trouble with oil blowing by out of the breather tube into the air filter area. I have replaced the tube and the little flapper that is down in there. And it still does it. Any other sugestions? Check the dipstick. It has a o-ring on it. If it is missing or cracked it will cause oil blow-by. Terry Share this post Link to post Share on other sites
