Onan Engine

[biltno 32]

Just want to say thank-you ahead of time for input. I've had  a 416-8 since new and recently bought a 520h cheap and other than a mower deck bearing it is surprisingly a great tractor! Anyhow I have been reading posts on here for weeks educating myself on the good and the bad. (mostly good) . The biggest thing troubling me is two issues with the engines. When referring to the rear cylinder cooling fins getting plugged with debris, is this something you can see without disassembly? or does the shroud need to be removed? The second question I have, both the 416 and the 520 have in the 800 range for hours. Do I need to adjust the valves because they get tight? Both engines  make no valve noise. Thanks again for anyone's input.

[TJ5208 1,824]

I would go ahead and take the shroud off and check on things. Another way you can vent the rear cylinder is by drilling holes in the belt guard. As for the valves i would wait for 1000 hours to hit the meter.

[pacer 3,173]

For sure remove the shrouds and inspect .... Its amazing what will accumulate behind them, and if its been sitting theres usually a wee mouse has set up house there.

 

When I bring a 'new' horse home I remove the shrouds, change all fluids (especially to NEW non ethanol fuel), inspect wiring, etc. This way you know where/when your starting point was -- and, you'll usually find something that needs attention.

[lynnmor 7,307]

First thing, apply penetrating oil repeatedly to all fasteners starting today.

 

It is time to adjust the valves, Onan may say 1000 hours but a tractor can have a wide variety of uses and abuses.  To adjust the valves you need to do some disassembly and that gives you the opportunity to do some improvement.   The exhaust needs to come off, so consider glass beading and painting it.  The intake needs to come off, so check for heat shields cutting into the edges and check to see if it is sealed.  The carburetor will be off with the intake, so take the top off and dump out the debris.  The valve covers will come off, so clean and paint them.  Use new genuine Onan gaskets and a torque wrench so you do not over-tighten any of the fasteners.

 

The belt shield holes are something I never did.  With that large flywheel forcing air thru it is a none issue.  The rear cylinder is next to the oil filter, so check to see if oil caused dirt to plug up the fins.  With the oil filter off you can see if there is a problem and maybe blast some parts cleaner in there, a flashlight and mirror will help.  If more cleaning is needed remove the head cover.  Removing the entire shroud may not be necessary and it is a pain to do.

 

Be sure to download the Onan Service Manual so you have the specifications for the valve clearance and bolt torque.

 

Come back and ask questions as you proceed.

[Ed Kennell 38,196]

Yes, remove the shrouds and clean the cooling fins.     With the tins off, look closely for an oil seep between the oil filter base plate and the engine block.   This plate is held in place be two bolts that have a history of loosening.   Remove the plate and clean the surfaces. Then glue a new gasket to the base plate and reinstall.     Any oil leaks around the filter are blown across the rear cylinder cooling fins where the  grass will adhere and clog the fins.

After cleaning, make sure the rubber oil filter gasket ring that seals the filter to the tins is in place.

[Handy Don 12,233]

3 hours ago, Ed Kennell said:

After cleaning, make sure the rubber oil filter gasket ring that seals the filter to the tins is in place.

This seemingly innocent bit of foam rubber is absolutely critical to proper cooling of the oil and the rear cylinder--DO NOT run the engine without one (they are the same on P216, P218, or P220)!

Replacements are cheap (<$10).

[kpinnc 12,067]

I'm gonna be THAT guy again...

 

While you're removing intakes and exhausts, and replacing gaskets, etc- you may as well pull the heads off and decarbon them. It's part of the 500 hour service anyway. 

 

And don't be scared to tear into these engines. The tins are the hardest part of the whole thing. 

[pacer 3,173]

11 minutes ago, kpinnc said:

may as well pull the heads off and decarbon them

 

That is a REALLY good suggestion!! Once the tins are off maybe take 2 minutes with an impact wrench. Will also give you an opportunity to examine the cylinders/valves and if you can, get a measurement on wear --- or, or hopefully ... not!

[Horse Newbie 7,071]

I did not decarbon my kinda new to me1994 520H, Onan P 220, but my new hour meter says 17 hours, so I’m good, right ?😆

[biltno 32]

Thank-you for all this great information! something is bothering me now... The 520H I bought used had maintenence records from the dealer. I used the 520 maybe 8 times to mow the lawn that takes about an hour. The seal that goes around the outside of the oil filter was missing. Did I cause damage from overheating it ? the engine sounded fine when I idled it down when i was finished. Obviously, I am not running the engine again until I replace it.

[Ed Kennell 38,196]

13 minutes ago, biltno said:

Did I cause damage from overheating it ?

Probably not.    If you overheated it enough to loosen the valve seat, it will let you know.

[Handy Don 12,233]

59 minutes ago, biltno said:

Thank-you for all this great information! something is bothering me now... The 520H I bought used had maintenence records from the dealer. I used the 520 maybe 8 times to mow the lawn that takes about an hour. The seal that goes around the outside of the oil filter was missing. Did I cause damage from overheating it ? the engine sounded fine when I idled it down when i was finished. Obviously, I am not running the engine again until I replace it.

Agree that probably haven’t caused much, if any damage, but I wouldn’t push your luck any further!

I AM startled AND disappointed that a dealer handling that machine would not have replaced that seal. Any tech who knows Onans would be all over that.

[Blasterdad 2,692]

1 hour ago, Handy Don said:

I AM startled AND disappointed that a dealer handling that machine would not have replaced that seal. Any tech who knows Onans would be all over that.

Doesn't surprise me a bit, I wouldn't take a push mower or anythig else to a stealership.

Finding anyone that knows what they are doing is getting increasingly difficult.

On the other side of that coin a shady tech left it off on purpose to cause failure.

A good friend of mine had a sealership take in her machine for service & new blades, when it was returned to her all they had done to it was change the oil & broke the rear fender, they had run into it somehow, they claimed it came to them that way.

Only after taking them to court did she get her money back. 

 

[lynnmor 7,307]

2 hours ago, biltno said:

Thank-you for all this great information! something is bothering me now... The 520H I bought used had maintenence records from the dealer.

All the more reason to do the basic maintenance we are talking about.  I had some warranty work done on my backhoe by a large dealer and it was returned to me with all six bushings missing.

 

With the oil filter seal missing you can run the Onan all you need to if you are just moving it around, just don't put it under heavy load.

 

I have pulled heads to de-carbon and never found enough to have made it worthwhile.  I run my Onans full throttle when working them, so that may be the reason for no appreciable carbon but in your case it may be a good idea to pop the heads since there is no way of knowing how it was treated.  If you are going that far, do a compression test first to see if the valves are sealing properly.  If you find low compression the valves are easily removed since everything is out of the way and no additional gaskets would be needed, only two valve seals.

 

Hopefully we are not scaring you too much, all the things mentioned in this thread are just normal procedures that many just ignore.  The bottom line is that treating the engine right should give you years of service.

[kpinnc 12,067]

4 hours ago, Handy Don said:

Any tech who knows Onans would be all over that.

 

So true. Unfortunately things like certification mean more now than understanding how to read a service manual. Freaking idiots these days, and it's frightening. 

 

The oil filter seal mentioned above is in the pic below. 

[NA73 70]

hmm, first I've heard about the oil filter to tins rubber. I don't think it was even mentioned in the onan p220g pdf but did see it after checking the 520h pdf - looks like toro# 82-0680.

Guess it's time to get one since mine didn't come with it.