ONAN P220 - could not believe the crud

[JackC 617]

I have a 1989 520HC with the ONAN 20hp p220 engine with about 700 hours on it.

I have owned it for about 2 years and it has been running fine until this year when I took it out of storage and the engine started to surge and needed more choke to stay running. I have been using Seafoam as a fuel stabilizer for storage over the winter.

I took the carburetor apart today to clean it and i could not believe the crud that was in it,

There was about a tablespoon of light brown powder in the bowl that looked like light brown sugar.

The fuel inlet hole where the fuel comes in and the float needle opens and closes was plugged with the crud.

Also, the engine was covered with grime that would inhibit cooling especially around the rear cylinder.

The rear cylinder of an aluminum block ONAN on a Wheel Horse 520H lives in a tough environment as far as cooling goes,

Perhaps that is why there have been so many valve seat and broken rod problems.

It would not be a bad idea to remove the air cleaner and thoroughly clean the engine every few years rather than waiting for a failure.

A vented belt guard and or remote oil filter is also a good idea.

Now that I have the intake and exhaust removed i will also check the valve clearances.

I will do a de-carbon in the fall when I take the tractor out of service and I can remove the engine for a more thorough cleaning..

Luckily there is a Mobil station nearby that started selling no ethanol fuel for $4.25 per gallon which I will start using.

You definitely need to go out of your way to keep those ONAN twins clean and cool on a Wheel Horse.

[Sparky-(Admin) 21,074]

Sounds like you have a good plan Jack. After I get my hydro foot control on my 416-H (ONAN) I'll be after a vented belt guard to help insure a long life.

Mike...............

[HorseFixer 2,012]

Sing it Brother Sing it! Yep dirt is a good part of why these Onans Rear Valve Seats Fail, but that is far from the only reason. The 60" Deck that was used on so many of these put quite a load on the Old Girl take that and mowing in hot temps and then running it up to the house and shutting her down without a running coold down period plus what you said dirt grime and a blockage of the fan either on the exhaust (belt gaurd) as Sparky mentioned, or plugged up around the Flywheel and that gives a perfect combination for disaster. The main thing is ya got it cleaned out before damage occured,

Cheers ~Duke

[sorekiwi 761]

I havent tried to work out why, but the fan system on the Onan flywheel pulls a ton more air than any other small engine I have ever owned. While mowing my (nearly) 2 acres with the Onan I have to lean forward and clear the debri's off the fan screen on both the front and back "straightaways",, any of the Kohler powered tractors its maybe every 2nd lap.

I guess that works both ways - it is super easy for the air intake side (the screen on the flywheel) to become blocked up, but when that inlet screen is clear the flywheel does move a bunch of air over the motor.

I'm still undecided on whether the belt guard has an effect. Venting it certainly wouldnt hurt, but I need to come up with a really nice way of doing it before I start chopping it up.

I've been pulling the shrouds of my motor at the beginning of spring and again 1/2 way through the summer, and havent been too horrified by the amount of clippings around the motor. My engine is relatively dry though, it wouldnt take much of an oil leak to collect a bunch of nastiness.

[JackC 617]

Heat build up on the back cylinder may be the prime cause of the valve seat failures on the Wheel Horse tractors with the Performer series engines. An oil cooler would help remove heat from the engine, or a fan on the back cylinder.

Simplicity put oil coolers on some of their models. There is a Simplicity oil cooler for sale on eBay.

Has anyone added an oil cooler to an ONAN on a Wheel Horse?

My 1996 Buick Roadmaster Wagon with the LT1 350 Corvette based engine has an oil cooler and the motor never runs hot even when towing.

[Brian K WheelHorse 28]

Here's how I vented my belt guard guys - real simple. I was concerned about how boxed in the rear jug was so I milled 1/2" slots in it. 2 of them actually end up under the plastic pulley cover when assembled: