Onan decarbon and vavle adjustment , plus other maintenance

[DrabHorse 1]

Hello all, I am soon going to decarbon and adjust valves on my Onan in a 97 520 with 1000 hrs.  I bought the tractor a few years ago with around 800 hrs.  I have been reading to see if there are some other things I should look at or replace at this time.  Any input or comments welcome on the following or any other issues?

 

1. replacing the gasket for the oil cooler,

2. heard somewhere about replacing a spring that regulates the oil pressure ?

3. something about sealing leaks on the two peice intake manifolds?

4. I'd also like to clean the carb while its off, is there a standard kit for that or just some individual gaskets needed?

 

thanks

[sorekiwi 761]

I'm not sure I would touch any of the things you mentioned unless you are having a problem.  I'd have a good look at everything while it is apart, and do a thorough cleaning of the cooling fins, but that's about it.  I would fit new valve stem seals on the inlets while putting it back together.

 

Not sure what you mean by the gasket on the oil cooler?  Do you mean the filter?  If its not leaking now, and the bolts are tight, I would leave it alone.

 

The 2 piece intake manifolds can leak, but if your engine is running well then I probably wouldn't screw with it.  Martin has described how he did his in one of his threads.

 

I've never had to buy a carb kit for an Onan.  I have always managed to remove the top, clean out the bowl and blow through the jets without destroying any of the gaskets.  Mind you I have never had a major carb problem either, if your motor is running OK now, I wouldn't get too carried away.

[Martin 2,130]

+2 on everything that Mike said. if its not giving problems don't touch it. the carbs can be done on the engine if you are careful with the top gasket. clean out the bowl and remove the idle needle and make sure its clean in the small holes and put it back together....

 

if its running ok just do the minimum, I'm sure you will get your fix working on getting it running well later on, especially if the carb picks up some junk from somewhere.......

[Ed Kennell 35,604]

                                                                                                                            If it is not broke ....don't fix it.

       I am in the process of redoing the onan on my 1988 520H  and have learned a lot from everyone on here.   The main issue with these engines seems to be keeping the cooling fins clean on the back cylinder.  They are not easy to work on. The wiring is a nightmare ... must have been designed by a demented electrical engineer.  Too many places for bad connections in all the fuses, connectors and switches.  I did have an oil leak on the oil filter mounting base and at the oil drain pipe that totally clogged the cooling fins and tin around the back cylinder. I did decarb and it was not bad at all. The intake seal looked good, so I did not reseal it. I did add vent holes to the belt guard to increase air flow across the rear cylinder.  The valves were in tolerance... no need to reset clearances.  Just cleaned the carb out with spray cleaner and reset the jet.

 

You can see some pics and read info on several recent posts in the TRACTOR FORUM   and ENGINE FORUMS  ;  

                                                                                               New? ..Find 

                                                                                               520H   Major oil leak   

                                                                                               My new to me 520H

                                                                                               Head gasket advice

Edited March 24, 2014 by ekennell

[DrabHorse 1]

Thanks for the info, sorry I did mean the oil filter mounting base, not oil cooler, I just said that out of habit from working on various cars that have those.

I've had the tins off before to clean, not too bad there, and I already have the belt cover vented.

I had not thought of the valve seals, thanks sorekiwi for bringing that up.

Edited March 24, 2014 by DrabHorse

[SAM58 30]

I have a question about this link...

 

"Onan decarbon and valve adjustment"

 

Is this a required maintenace at certain hours on the clock 500, 1000, Ect...

 

or if it is just not running right?

 

 

I always thought it best " if it's not broke don't fix it"

 

I use Sea Foam & stabil in my gas or does that even help?

 

   

[MalMac 1,328]

Doing a decarbon and valve adj, comes under the heading of "Preventive Maintains". You do this to help prevent problems form happening down the road. Carbon does get built up over time and valves wear. The Onan is prone to valve seat problems. Now that I said all that with the saying "If it ain't broke don't fix it" I know it's hard to tear something down if it's running good. I myself am facing the same problem. I have a Onan that I don't know the history on real well. This motor is strong as anything and runs just perfect. Starts the instant you hit the key no matter what the temp is outside. No knocks, pings, smoke nothing. To tear into it just seems wrong. So I am on the fence on what to do. I am a believer in PM. but tearing this one down to decarbon and adj. the valves when there is no indication it needs it i just don't know.

[shorts 182]

The decarbon is a  scheduled factory PM procedure, if carbon builds up enough it can cause an interference issue between the piston and cylinder head and cause a catastrophic engine failure, I too am a if it ain't broke don't fix it guy , but PM service is intended to prolong the life of the engine so you don't have to fix/overhaul/replace it prematurely. the valve adjustment is considered routine maintenance for proper engine performance and durability.

[DrabHorse 1]

I'm back to report what I have found working on the Onan.  Everything came apart well, but I had to take some time with a couple of the bolts working them in and out with pb blaster.  I noticed the edge of one of the exhaust heat shields was starting to wear a groove into the intake manifold, but it did not look like it was worn all the way through but could be getting close.  I plan to trim the heat shield some and put some jb weld or something on the intake.  It looks like one of the intake valve oil seals was leaking because that port was much more oily than the other one, I am glad I have the new oil seals.  I did not think there was alot of carbon build up in there at first, but after cleaning everything I guess there was a fair amount.  It took awhile to clean and what was on there was really hard. 

I was really hoping to put the engine back together in the next couple days, but I think I need the valves and seats machined.  When I hold the intake valves against the seats and shine a small bright light down into the port I can see light between the valve and seat.  When I do the same with the exhaust valves no light can be seen.

Edited May 5, 2014 by DrabHorse

[AMC RULES 36,941]

Thanks for the updates...    

sounds like you're making good progress with it. 

[Tankman 3,515]

Try SeaFoam carb spray?

[DrabHorse 1]

I took the engine to a shop to get the valves and seats ground / cut.  They should be doing it sometime this week.  Hopefully everything goes well, and I hope the seats don't decide to come loose anytime soon after having put this work into it. 

 

I have been thinking about a problem I had with a slight vibration in this engine the last half of the mowing season last year (I had even started a post here about it).   I never did find anything more about that and now I'm wondering if it could have been leaking valves causing an unbalance between the two cylinders.  I had checked the compression and I don't recall what it was exacty, but at the time I didn't think it too far off.

[Jim Piver 0]

On ‎5‎/‎8‎/‎2014 at 2:40 PM, Tankman said:

Try SeaFoam carb spray?

Seafoam?...PFFFt...Save your money.

[ZXT 2,394]

1 hour ago, Jim Piver said:

Seafoam?...PFFFt...Save your money.

Resurrected a 5+ year old thread for nothing, but that's cool I guess.

 

I'll be the first one to say that SeaFoam is amazing stuff that works wonders. I agree that not everything can be fixed with a chemical, and I assume your one experience with it didn't result in a fix. Most of the time it does though.. from cleaning fuel systems, to de-carboning combustion chambers, to freeing up stuck lifters, I can assure you that it works quite well.