Yikes my Onan is smoking!

[papaglide 542]

Well the Onan on my 1996 416-8 is starting to spew light, wispy white smoke out of the exhaust on occasion while its running. It releases slightly more when throttling up and turning on the pto. It has 962 hours on it and now I am fearing that it is in need of a rebuild. I know that it is burning oil, I cut the grass yesterday for 2+hrs and my oil was down about 4-6 ounces after it cooled and I checked it when I finished.

Let me preface that while I change the oil and do maintenance and light mechanical work on my tractors, I am by no means an "engine rebuild type" guy! I would rather leave that to the ones that know what they are doing!

Would it be cost effective to take it to the local Wheel Horse (now Toro/Kubota) dealer for a rebuild if needed? Is it ok to continue operating the tractor and just replace the oil when needed? I am not quite sure what to do with this one as this hasn't happened before.

Edited May 5, 2013 by papaglide

[Tankman 3,523]

I'm not a "motor head" either.

I might note that at times, needing an Onan part, my local RV dealer has them.

From what I understand Onan's are used extensively in RV's.

You might check in your location.

[Dieselcowboy 210]

Parts for these are rather expensive. Might find a kohler replacement.

[Forest Road 594]

There's a lot of differing opinions as to what to do, the purists rebuild. The rest of us repower. I'm building a kohler Mag 16 for myself right now. You'll see guys go w twin vanguards, Hondas, and kohlers. It's all about keeping the horses and our many attatchments in use! Best of luck!

[Irv 115]

Very expensive to rebuild those Onans-if the parts are available. I would run it 'til it dies and look for a Kohler (or a junk tractor with a good Kohler) or consider one of the Honda clones like at Harbor Frieght.

[Tankman 3,523]

 

Very expensive to rebuild those Onans-if the parts are available. I would run it 'til it dies and look for a Kohler (or a junk tractor with a good Kohler) or consider one of the Honda clones like at Harbor Frieght.

My 520-8 has an Onan. I know nothin' about it other than I'm a stickler for PM (preventive maintenance).

I too would repower, never had a problem with my Kohler engines!

Repowering with a Kohler engine is where I'm goin' if this Onan quits. :smile:

[546cowboy 302]

I've never had one blow white smoke. I have had a 520H that used about a quart of oil about every 4-6 hrs. but it still ran great for over a year until I found another Onan to replace it with. I would just keep using it and be on the lookout for another Onan. They are really great engines.

 

Yes they have been using Onans for years in generators and welders. They also had P series engines in JD's and the older Onans in everything from Craftsman to Case/Ingersall tractors. New parts are more expensive but Kohler is going the same way. But you can buy aftermarket parts for a Kohler and you can't for an Onan.One of those replacement Honda's would run you around $1500 by the time you were done. Any new twin horizontal shaft engine would be anywhere from $1200 on up.

Edited May 6, 2013 by 546cowboy

[papaglide 542]

So I can run it and just keep the oil filled and there won't be any harm to the engine? That is good news to me. I am no motor head so replacing it isn't an option, money wise it isn't an option either. Maybe I run this tractor and then pass it on to someone who can replace the engine when its needed.

[dbartlett1958 99]

Mike,

 

Keep a close eye on the oil level and run it.  Oil is relatively cheap and you may go a long time as it is.

[papaglide 542]

Thanks everyone for the help. I feel very reassured now regarding my tractor.

 

Mike,

 

Keep a close eye on the oil level and run it.  Oil is relatively cheap and you may go a long time as it is.

David, thank you. That sounds like a plan and one that this "no motor head" can handle!

[JackC 617]

It may just need the de-carbon service and have the valves adjusted if that has not been done.

Some do the service to get over 2,000 to 3,000 hours out of their engines and some don't bother and just run the engine until it destroys itself.

 

The ONAN P Series needs the de-carbon and valve service after about 500 hours and I would not go beyond 1,000 hours without doing it unless you don't mind replacing it.

[papaglide 542]

What does the decarbon service entail? What does the valve adjustment entail? Remember, I am not an engine guy. I guess what I am basically asking is would it be expensive to have these services done or would it be easier to trade/sell this tractor to someone who can do the engine stuff?

[eric46986 0]

I was a Toro / Wheel Horse mechanic for about 10 years, but I've been out of the business since 2000.  I can tell you this about those Onan engines, they're not all they're cracked up to be.  I'm generally a fan of rebuilding, rather than replacing an engine, but those Onans have aluminum blocks, and every one I've ever torn down that was burning oil had exactly the same problem..... The cylinders were totally out of round, and would required having the block bored beyond the size of the largest available pistons (at the time) just to get a new set of rings to seat.  Your best bet would probably be to start running a little thicker oil for right now, and start looking for a cast iron Kohler Magnum to rebuild.

[leeave96 490]

I think you got several options.

 

1.  Run the tractor until it breaks.

 

2.  Do more diagnostics and see what you've got.  If you are not up to doing the service yourself, you might find a good mechanic that can do it - with a limit on how much you are willing to spend up front.

 

3.  Sell the tractor.

 

4.  Keep the tractor and do #2 to the extent you don't ruin the engine and then #1 until it breaks.  While all of this is going on, find yourself a single cylinder Kohler K341 out of a 16 hp Wheelhorse for a transplant.  Simple engine, cast iron block, lots of power - plus all the features of the 520H, like swept forward axle, etc.  Another route is to keep an eye out for a donor Onan engine.

 

Bottom line is - don't get in a hurry to do anything.  Take it a little at a time and enjoy the ride.

 

Good luck!

Bill

[MarkPalmer 81]

I would just top the oil off before you run it each time- after all you can buy a 55 gallon drum of oil for less than what an Onan costs to rebuild today.  When the Onan does take its final poo or gets too smokey to tolerate, drop a used or rebuilt Magnum 18 or 20 on the frame. 

 

-Mark-

[papaglide 542]

Everyone, I really appreciate the input. That's what makes this sight awesome! My plan thus far:

 

         1. I won't run it until it breaks, that would be downright wrong to me!

         2. I will keep topping it off and tolerating the wiffs of smoke and smell.

         3. Leaning toward selling/ trading. I see issues in the future that I don't want to really deal with.

 

What simple diagnostics could perform? In the meantime I am going to talk to my local dealer regarding an estimate dealing with the engine.

 

I will enjoy the ride, this is the most comfortable riding tractor I have ever had!

 

Thanks.

Edited May 7, 2013 by papaglide

[JackC 617]

The front cylinder head can be removed easily and checks made for carbon build up that could prevent the valves from closing properly allowing oil to get into the combustion chamber.  The cylinder could also be easily checked for wear or out of round or glazing.  If the cylinder appear to be OK then it may be worth going further and checks can be made for worn valve guides and seals and valve adjustments could be made.  If the cylinder is out of round or excessively worn then you may just want to put more oil in it instead of money and keep an eye out for a used replacement ONAN or Kohler.  You can't beat the sound of the ONANs or the reliability of the cast iron Kohler flat heads.  A used ONAN would be the easier transplant due to the wiring.

[Keith 21]

those Onans have aluminum blocks, and every one I've ever torn down that was burning oil had exactly the same problem..... The cylinders were totally out of round

 

The alloy P-series block also explains the problems with the valve seats.  I think the earlier B series Onan also had an alloy block but isn't known for valve seat failure.     If Onan had stayed with cast iron blocks, other than being much heavier, I think these motors would have had as good a reputation as the Kohler.   The cast iron Onans from many years ago just kept going, but most were used in generator sets where the cooling fins can be kept clean, and I think they run at 1,800 RPM.   David Onan was a stickler for dependability, which is why he manufactured his own motors for his generator sets, but that was decades before the P series.  The old iron Onans must have been very heavy.  David W Onan made several different products, includes lathes:

    http://www.lathes.co.uk/onan/

[eric46986 0]

 

those Onans have aluminum blocks, and every one I've ever torn down that was burning oil had exactly the same problem..... The cylinders were totally out of round

 

The alloy P-series block also explains the problems with the valve seats.  I think the earlier B series Onan also had an alloy block but isn't known for valve seat failure.     If Onan had stayed with cast iron blocks, other than being much heavier, I think these motors would have had as good a reputation as the Kohler.   The cast iron Onans from many years ago just kept going, but most were used in generator sets where the cooling fins can be kept clean, and I think they run at 1,800 RPM.   David Onan was a stickler for dependability, which is why he manufactured his own motors for his generator sets, but that was decades before the P series.  The old iron Onans must have been very heavy.  David W Onan made several different products, includes lathes:

    http://www.lathes.co.uk/onan/

 

I'm sure you're right.  I did more valve jobs on those P series engines than I care to think about, and it was usually the rear cylinder that lost the exhaust seat (less cooling than the front cylinder, I assume).  There was also a LOT of excessive carbon build-up on the heads and pistons, especially when someone tries "saving wear & tear" on the engine by running it at 1/2 or 3/4 throttle.  There's a reason they're governed at around 3400RPM.  All-in-all, a very sweet running engine when it's new, but I wouldn't give you a nickel for one with 1000 hours on it, especially if I didn't know exactly how it had been run and maintained.