Calling All Horse Gods

[Brandonsj04 0]

Newbie here, first post. Let me start off by saying how much I already appreciate this site and all of the knowledgable members it has. Have been lurking around gathering a bunch of great invaluable information from you members behind the scenes . I have recently inherited a 1988 520h that was bought by my grandfather. He passed some 18 years ago, and once my grandmother downsized, I received this beast of a machine. Starts right up and runs great, the only problem is the dreaded oil burning gnome that lives inside the 20hp Onan . It has 657 hours on it, which I gather isn't too much as my research shows these engines can go 1500-2000 hours before a rebuild. Compression test shows 125 on front cylinder, 115 on back. No knocks or terrible noises. No smoke upon start up, just noticable when engine is under load or giving it more throttle. I have read that these engines do burn some oil, but I don't think it should be shooting out puffs of blue smoke over 2500 rpm's. I want to fix the problem, as I am being shy with the machine thinking it's going to break down, not really harnessing it's full potential. Am I ready for a full blown rebuild, or will a hone and ring job fix my oil burning problem? I know I can't get a concrete answer until I tear down, but just looking for some opinions from members who have much more experience with these line of engines.

:)

[dryrun 0]

HELLO, and WELCOME. I am not much on ONAN, more of a kohler person, but at 657 hours, I would suspect you are pulling oil out of the crankcase thru breather. I would highly reccomend a leak-down test to see where air is going. I ran these engines for years on portable welders with a lot of hard running hours and no problems. Of course sitting around for years also takes its toll on oil-control rings. But again, I firmly beleive in shooting air into cyl, and see where it goes.

Don't be too quick to tear down, this site is well stocked with with people who have seen a lot, done a lot, and been there done that. I'm sure you will get the best help from them.

Again welcome and never be afraid to ask.

GEORGE

[HankB 16]

Another test would be crankcase vacuum at idle. I'm not really sure how to interpret the test, but it might indicate blowby (less vacuum) or breather problems (more vacuum?)

Be sure to let us know what you find. I have a Kohler (K301) with what sounds like the same symptoms. It's a smoker and does not produce a steady stream of smoke. It tends to put out puffs and when it does, it stumbles at the same time. I think it is a breather problem and the first thing I plan to do is to pull out the breather and figure out if it is working right. It seems to me that it is sucking slugs of oil into the intake that result in both smoke and stumble.

And BTW,

-hank