Important info to keep your Onan happy

[artfull dodger 441]

Most guys will discuss the pros and cons of the Onan engines till the cows come home. But to keep these happy, four simple things need to be done.  The most important is making sure your rubber grommet around the oil filter that seals it to the cooling tin work is in place. Most every Onan I see is missing this on garden tractors.  A very simple $6 part, but HIGHLY important to keeping that rear/right side cylinder cool.  Without this little rubber part, you loose 30% of your cooling airflow on that side.  And that figure is from Onan themselves and does not take into account the belt guard helping restrict cooling air flow on our Horses.  Second thing is to do your valve lash adjustment sooner than the book says.  In Onan factory schooling they taught us every 250ish hours vs the 600 in the book was the best practice.  Valves being held slightly open is one the huge reasons we see popped valve seats on engines.  Add in the missing grommet on the oil filter and we have a perfect storm to overheat the engine and superheat the valve seat=popped seat or thrown rods. Three...keep it clean, when you change the oil, clean up your mess, wipe it all down in there, shine a flashlight in there and look, is the seal under the flywheel seeping, or is the jug oil/grime free and dry?  Pulling the left/front side cylinder head tin every spring or every oil change is good practice to check for the same along with rodent nests.  And finally, run them at full throttle at all times after starting and till just prior to shutting them down.  Onans do not tolerate overheating from extended RPM use like a Kohler can.  Just nature of the beast and the design of the engine coming from the generator world.  Once she is running, throttle up before driving off, drop back to 1/2 to 3/4 to engage PTO, then right back to full power 3600rpm + or - 50rpm with the PTO engaged.  Nothing in the small engine world can match the snarl and power of an Onan B or P series, they just take a bit more upkeep to keep them happy.  Mike

[lynnmor 8,853]

Actually every thing that you mention is for any small engine with the exception of keeping a good seal on the oil filter.  Onan generators ran at 1800 RPM all day with a full load, those engines were the same except for the governed speed.  But yes, run them at 3600 RPM when worked hard.  I would add that keeping the fuel system clean so that the fuel air mixture is correct, lean mixtures can overheat valves.  I helped a guy with a Kohler that had burned valves every season because the dealer leaned the carburetor every time he worked on it.

[artfull dodger 441]

yep, and a leaking intake manifold on an Onan will make her lean, hence the surging.  Onans are just much less tolerant of anything out of spec than a Kohler.  The valve adjustments are unique to the Onans in the older flat twins.  Kohlers you set via grinding when the engine is built or rebuilt with new valves.   Wasnt till the OHV engines of modern day did we see adjustable valve lash return and become a service item that needs checked.   

[bds1984 1,511]

On 9/4/2024 at 12:48 PM, artfull dodger said:

yep, and a leaking intake manifold on an Onan will make her lean, hence the surging.  Onans are just much less tolerant of anything out of spec than a Kohler.  The valve adjustments are unique to the Onans in the older flat twins.  Kohlers you set via grinding when the engine is built or rebuilt with new valves.   Wasnt till the OHV engines of modern day did we see adjustable valve lash return and become a service item that needs checked.   

 

I've done the grinding trick on many engines, but my K341 has adjustable lifters on it.  Get them out of adjustment too much and you'll hear it.  

[artfull dodger 441]

They will tap if they are out of adjustment to the wider side.  Sadly Onans close up usually, not the other way around.  You want to hear an Onan being a bit tappy when its idling.  New OHV engines are also adjustable.  Briggs are bad for going wide and loosing the compression release making the starter unable to roll them over.  I remember Kohler had a Command series that had hyd lifters that were self adjusting.  Was one of the noisiest clacking set ups they ever came up with.  Had plenty of customers complaining about the racket they would make and swearing they needed to be adjusted.  Not one of Kohlers better ideas.     

[CaptainDad 0]

On 9/4/2024 at 10:14 AM, artfull dodger said:

The most important is making sure your rubber grommet around the oil filter that seals it to the cooling tin work is in place. Most every Onan I see is missing this on garden tractors.  A very simple $6 part, but HIGHLY important to keeping that rear/right side cylinder cool.

Since I’m new to the Onan engine, would you please share a link to the part you are talking about or a part number. 

Thanks, 

Mike

[sqrlgtr 3,041]

6 hours ago, CaptainDad said:

Since I’m new to the Onan engine, would you please share a link to the part you are talking about or a part number. 

Thanks, 

Mike

Hard to find that particular seal now and todays price is way higher than 6 bucks. Engine Related Parts & Kits | Case Ingersoll Tractors Northeast | Connecticut these guys carry a aftermarket one but I prefer the original type myself and they are still out there but getting harder to find but the aftermarket beats nothing. 122-0502 -C, C20577 Onan Oil Filter Sealing Grommet To Heat Shield Replacement thats the part number for the aftermarket one and cant seem to find the factory # at the moment but you just google it.... here ishttps://onanparts.com/index.php?main_page=product_info&cPath=1_7_22&products_id=296 alink to the factory style 

Edited May 5 by sqrlgtr

[sqrlgtr 3,041]

3 minutes ago, sqrlgtr said:

Hard to find that particular seal now and todays price is way higher than 6 bucks. Engine Related Parts & Kits | Case Ingersoll Tractors Northeast | Connecticut these guys carry a aftermarket one but I prefer the original type myself and they are still out there but getting harder to find but the aftermarket beats nothing. 122-0502 -C, C20577 Onan Oil Filter Sealing Grommet To Heat Shield Replacement thats the part number for the aftermarket one and cant seem to find the factory # at the moment but you just google it.... here is a link to factory style https://onanparts.com/index.php?main_page=product_info&cPath=1_7_22&products_id=296

dont know how I posted above this way was trying to edit my first post but maybe you can make sense out of it.

Edited May 5 by sqrlgtr

[wfopete 24]

Check with Performance Saw Supply.  There website sucks but they have it on Evil Bay I have one coming now as well as other Onan parts.

 

 

 

 

[kpinnc 18,502]

On 9/4/2024 at 10:14 AM, artfull dodger said:

Most guys will discuss the pros and cons of the Onan engines till the cows come home.

 

Or in the case of the P220 specifically, some of us just replace them with something better. 

 

I absolutely agree with your maintainence points, but having seen meticulously maintained P220 engines fail several times, I'll take my chances with something else that I can at least still get parts for. 

 

I will say this: the P216 and 218 seem to be less prone to the weaknesses of the 220. Since the only real difference between them lies in the cam setup, I guess it is the culprit or at least a contributor. 

 

I would happily run a P216 or P218 any day. They are decent engines. But I have no use for a P220. 

[lynnmor 8,853]

11 hours ago, kpinnc said:

 

Or in the case of the P220 specifically, some of us just replace them with something better. 

 

I absolutely agree with your maintainence points, but having seen meticulously maintained P220 engines fail several times, I'll take my chances with something else that I can at least still get parts for. 

 

I will say this: the P216 and 218 seem to be less prone to the weaknesses of the 220. Since the only real difference between them lies in the cam setup, I guess it is the culprit or at least a contributor. 

 

I would happily run a P216 or P218 any day. They are decent engines. But I have no use for a P220. 

 

So you think that a .030" additional lift on the intake cam lobes makes the P220 a worthless engine?

[Bill D 2,894]

I too prefer the P216 over the P220.  I've passed on several nice 520's over the years due to that engine.   For whatever reason the P220 just seems to be more failure prone than the P216.  Personally I don't need 4 more horsepower to run my 48" deck.  Far from a worthless engine, but more engine than I need.

[sqrlgtr 3,041]

Well, I will take up for the p220 but I'm kinda biased the only two Onans Ive been around are the two I have on 520h"s. They don't get worked like they used to in their former life but haven't had any trouble after a little TLC when they came home with me. If the $$$ is right I will take a chance on a P220 any day.

[kpinnc 18,502]

1 hour ago, lynnmor said:

So you think that a .030" additional lift on the intake cam lobes makes the P220 a worthless engine?

 

No sir. I think an engine that has a very high percentage of losing a valve seat because it was a poor choice for this application which at best makes it a liability. As I said the P216 and 218 do not typically have the same fault. 

 

I wasn't casting damnation at the brand or model. I was stating my personal unqualified opinion. There won't be a P220 engine on anything that I use unless it has some upgrades. 

 

For example: I have a Toro Groundsmaster that uses a P220. That engine has over 3000 hours on it, and it will still run if fresh gas gets to the carburetor. The difference is that it has no obstruction on the cooling fins, and is equipped with a very large remote oil cooler and oversized filter. It takes nearly 4 quarts of oil to fill it. Point being?  Toro either knew the engine had special requirements or clearly placed  emphasis for longevity on that machine for thier commercial line during the same time the 520 tractors were being produced. 

 

I think the Onan P220 engine was a poor match for a Wheel Horse. In the very least there should have been additional systems to help it run cooler in such a restricted location. 

Edited 4 hours ago by kpinnc