Onan engine longivity tips?

[Economy Bob]

Just got a Toro mower with a 20 hp Onan opposed twin. Engine has 1700 hrs on it according to the meter. Are there any tips out ther to encrease / prolong the runabillity of these engines? I havent had much luck with them in a past experience.

[John Dunn]

I've heard the 2 cylinder opposed engines as used in older John Deere and other lawn tractors tend to run out of oil when used on hills. Note all were Onan and it might not be a problem if you keep an eye on the dipstick. Makes sense if the engine was designed for stationary use. Good luck!

[Dave R]

I have seen a lot of them have valve seats on the exhaust come loose and things go to heck. I think that people dont pay enough attention to keeping grass chaff cleaned out of air passages and the block gets hot and the seats get loose. The the hydrualic oil cooler over the cooling air intake dont help much either , especially when covered with a mat of stuff. Also, keep the engine speed up a bit...onans are runners not luggers.

[dkamp]

Air-cooled boxer engine failures weren't the Onans, it was the Kohler KT17 "series 1". that engine employed pressurized mains, but 'spray' lubrication of everything else, and it would not properly lubricate when on a sidehill.

The Onans were much more solid.

It's a flathead engine, so it will build up carbon soot inside the chamber, and will get require cleaning out. As others noted, keep debris out of the cooling-airflow path, and change the oil on regular intervals.

[Sky]

There were the twin onans which were the "boxers" on the 520 Wheel horses that had a rep. of loose valve seats. I think this problem was addressed by the factory but i dont remember how. Dave R is right. Onan had this very problem. I recently had a 520 WH i had to get a new block for becouse the seats on the old block were out. Myself i wouldnt have an Onan for multipul reason. But thats ME.

[Andy Moss]

I worked on many of them in the Deere garden tractors and every valve seat I saw come out was on an engine with dirty fins. Now you can get .010" oversized seats from onanparts.com. I have peened quite a few, as that was an inexpensive fix, and most didn't want to spend the money.
Also seen Kohler, Honda and Briggs loose seats.


The key to longevity is the same as any other. Maintenence!

[ehpower2]

another popular thing i have done and it expensive 2 repair but if it runs out of oil it could shear most of the gear teeth on the cam wreaking havoc on everyting also the bearing on the cam shaft usualy goes 2