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Chestnut

520-H Onan surging issue

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Chestnut

 

I've seen this issue discussed in a couple of different threads and I know the first step is to clean the carburetor. My 520H tractor with the Kwik-Way loader and original Onan engine has the dirty carburetor problem and needs ¼ choke to run smoothly. It is also hard to start, especially in cold weather. How long should it take to pull the tins, carb, and manifold and reinstall after the carb is clean? If it's relatively quick to disassemble and reassemble I actually have a Chinese knockoff carburetor I could install while I get the original cleaned and sorted out. 

 

I plan to replace the fuel line. I have a couple of feet of the line, but an estimate of how much I'll need in total would help if anyone has that information.

 

Should I adjust the valves and decarbon the cylinders while it’s apart? Adjusting the valves seems a no brainer, but I wonder about pulling the heads to decarbon. Is there clearance to pull the rear head without unbolting and moving the engine? I’m assuming the rear cylinder is #2. When I looked at the Onan manual online it looked like the torque pattern for #2 was a mirror image of #2. Anything else I should be looking for when I’m in there? The tractor is at my mother in law's and I usually visit for a few days with a chore list and at least a rough timetable.

 

I just joined the forum so I just saw the posting about resealing the intake manifold. Is this a common issue? I haven't sprayed around the manifold or gaskets with carb cleaner while the engine's running to check for vacuum leaks, but I guess that's another step to take before starting to tear things apart.

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TractorJunkie

Surging, take the top of the carb off and you will need to clean the jetting ports and the float bowl. After you remove the air cleaner and mounting plate, just a flat blade screwdriver, carb cleaner and clean paper towels should be all that is necessary. Compressed air would be a big plus to blow out the debris in the bowl. The carb doesn't need to come off to do this cleaning. That would be a good time to replace the fuel line and filter Don't be surprised if you need to clean the carb more than once. All the other stuff is nice to do and can be important but being it is on a machine that is not run much, it is up to you. Checking the valve lash is not to time consuming like taking off tins, heads and cleaning, this can tie up time and is tough when your working somewhere other than home. 

One other thing, make sure you are using a gas additive to remove the water in the fuel. Machines that set are water to fuel magnets. 

I am by far not an Onan expert, just more tinkering than anything. There are some people here that can take those things apart with their eyes closed. I am sure one of those experts will be along and may be able to point you at a thread on this subject and offer more sound advise. 

Welcome to the square!

 

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lynnmor

I remove the engine mounting bolts and turn the engine to decarbon the rear cylinder, however I have never had excessive carbon.

The heat shield tins often cut into the intake manifold, so grind a bit of clearance if they touch.

The intake halves can leak, its just the luck of the draw.

Removing the major tins is only necessary if you need to do a thorough cleaning of the fins, it is a pain to remove the coil and other parts to make that happen but it might save you from major problems.

Be very careful removing and installing both the intake and exhaust mounting bolts, they strip easily.  If you can start soaking all fasteners with penetrating oil days ahead it will help.

 

I would never put a well used Onan in service before doing a decarbon, valve adjustment, intake inspection, carburetor cleaning and painting the exhaust system.

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Ed Kennell

:text-welcomeconfetti: to the :rs:Chestnut.        You have all ready great advice from Joe and Lynn.   

    I will only add what I found when I got my neglected  '88 520 a few years ago.

It took three carb cleanings to finally solve the surging problem.

If you do remove the tins, and I feel you should,  check for oil leaks under the oil filter base plate.  It is attached with two bolts and has a very narrow sealing gasket to the block.

Any oil drip there is blown across the rear cylinder cooling fins creating a sticky collector for grass clippings.  Also make sure the oil filter is sealed to the tins with the rubber grommet.

These are a couple things that contribute to the rear cylinder overheating problem.

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Chestnut

Thanks for all your input. The idea of trying to clean it without taking it and the manifold off the engine sounds good to me. When i wake it up in the spring I'll change the fuel line, start it up, check for vacuum leaks with some carb cleaner, then clean the carb in place by taking the top off and going after all I see with the cleaner, a nylon brush and compressed air. Repeat as needed. I have about four feet of new fuel line and a box of spring clamps from another project.

This tractor doesn't get a lot of use, probably less than 20 hours a year and only has about 620 hours total. 

Thanks again for the advice..

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cleat

Be sure to unscrew, remove and clean the brass idle jet as it has tiny holes that plug easily.

 

You can also unscrew then clean the idle mixture screw and the passage behind it with carb cleaner.

 

Go easy with the compressed air, I blew the welch plug out of one of mine a couple of years ago and had a heck of a job finding it to replace it.

 

 

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Tuneup

This is timely, thank you. I had to replace the plug on my'16 and used a flat battery. The backing is rigid enough and grinds easily on a dremel. stays in place with the old Permatex glue. Carb looks really good otherwise but I cleaned it and applied a kit anyway. You'll hate me but I used Permatex Ultra Gray along the seam in the intake. Now, thanks to your info, it will sit while I pull the tins and heads. May as well get in there good because who the heck knows what I'll find. Thanks!

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Tuneup

Not meaning to hijack the thread, just a final update. Pulled the front head. Carboned-up mess. Bore looks good. Pulled valve covers - valves read .003 and .013. Valve chamber cooked grimy. Time to remove the valves, clean and give a good lap. Intake seat OK. Seems this one either ran a bit hot or the oil was run too long or both. The pocket between the ports was stuffed with dirt but the fins were all clean. I'll get to the rear tomorrow. The former owner wired a fan to the hood on the light circuit to keep it cool - was aware of the issue and got on it. We'll see. When it's all done, I'll know if the surge is cured!

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Chestnut

Tuneup, glad to read that you were able to open up that engine and start to deal with the issues you found. 16 degrees when I took the "new to me" machine out to clear a little snow. Definitely too cold to be wrenching unless there's heat. Maybe April. Good luck.

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Tuneup

Maybe NOT today. It's 33 outside and I'm on a hillside so the wind is pushing 30 MPH. The days of installing cast iron 4-speeds in Chevelles in our northern NJ driveway are long past for me. 16 degrees? no.... Stay warm!

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lynnmor
10 hours ago, Tuneup said:

Not meaning to hijack the thread, just a final update. Pulled the front head. Carboned-up mess. Bore looks good. Pulled valve covers - valves read .003 and .013. Valve chamber cooked grimy. Time to remove the valves, clean and give a good lap. Intake seat OK. Seems this one either ran a bit hot or the oil was run too long or both. The pocket between the ports was stuffed with dirt but the fins were all clean. I'll get to the rear tomorrow. The former owner wired a fan to the hood on the light circuit to keep it cool - was aware of the issue and got on it. We'll see. When it's all done, I'll know if the surge is cured!

Grind the valves, don't lap them.

I can't see any way that an electric fan would do a bit of good, sounds like the PO was clueless.

Make sure that you have the 122-0502 Oil Filter to Shroud Gasket in place.

Replace the intake valve seals.

Operate the engine at full speed when working it and at a rather high speed at all other times.

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peter lena

chestnut, in addition to your work above , that entire  fuel system needs to be refreshed and REGULARLY ADD A CLEANER , LIKE SEAFOAM TO YOUR GAS. letting that engine heat up under load and using a high detergent fuel cleaner will really help things out. you could also add some vent holes to the  drive belt guard plate to increase that engine cooling. pictures on this site for that , pete

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peter lena

fund some pictures i would favor the rear cylinder area , pete , 

 

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tom2p
2 hours ago, Tuneup said:

Maybe NOT today. It's 33 outside and I'm on a hillside so the wind is pushing 30 MPH. The days of installing cast iron 4-speeds in Chevelles in our northern NJ driveway are long past for me. 16 degrees? no.... Stay warm!


 

lol brings back memories - bad memories 

 

many years ago we did a trans swap in freezing cold garage and I was sick for the next two weeks 

 

and I think it was a cast iron 4-speed ... Saginaw ...

 

 

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tom2p
13 hours ago, Tuneup said:

Not meaning to hijack the thread, just a final update. Pulled the front head. Carboned-up mess. Bore looks good. Pulled valve covers - valves read .003 and .013. Valve chamber cooked grimy. Time to remove the valves, clean and give a good lap. Intake seat OK. Seems this one either ran a bit hot or the oil was run too long or both. The pocket between the ports was stuffed with dirt but the fins were all clean. I'll get to the rear tomorrow. The former owner wired a fan to the hood on the light circuit to keep it cool - was aware of the issue and got on it. We'll see. When it's all done, I'll know if the surge is cured!

 


I believe quality motor oil - changed regularly (if not fairly frequently) - is a must especially for an Onan to provide long service life 


gotta keep on top of oil changes - and especially if using mineral based oil (as opposed to synthetic)

 

many top mineral based oils will lubricate / protect as well as top synthetics - but will break down faster and then will not protect as well at high temperatures 

 

 

Edited by tom2p

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Tuneup

Thanks, guys - taken to heart. This is the 16 so no oil filter, right? I'm a Briggs, Tecchy, Kohler guy so am starting fresh at 58 years of age with this twin. The vent atop the fan shroud is missing and he left it uncovered. Oh, that fan is radiator quality so about 12" across. It's like a jet engine under there. I am enjoying this!

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cleat

Any 16 twin Onan I have ever had came with the oil filter.

These should have all the engine tins in place for proper cooling.

 

They really do move a lot of air so it is a wonder that they ever overheat.

 

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tom2p
14 minutes ago, cleat said:

Any 16 twin Onan I have ever had came with the oil filter.

These should have all the engine tins in place for proper cooling.

 

They really do move a lot of air so it is a wonder that they ever overheat.

 

 

 

agree - they do move a lot of air 

 

maybe the air flow not getting to rear cylinder properly ?

 

or failures due to excess temps because air flow impeded due to screen obstructed by grass clippings, leaves etc ... and/or cylinder fins full of grass, etc 

 

oil filter gasket not installed 

 

or 

 

excess / high operating temps due to lean condition 

 

or 


oil related - excess running with low oil level (due to excess oil consumption etc)  ... or degraded oil ... 

 

the Onan engines are air / fan cooled - but the initial cooling of the internal engine parts is provided by the oil

 

 

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Chestnut

These tractors with Onans are all 25 years old more or less, so unless you've owned it yourself for that long you have to take what you get and try to correct any issues that have cropped up due to age, use, neglect, bad fuel, bad maintenance, and so on. I'm curious to find out how many hours the engine Tuneup is working on has to have that much carbon? The manual says to clean carbon every 1000 hours, but we all know that trouble could happen in fewer hours with poor maintenance, clogged carburetor, overheating, short run times so the engine never really warms up and so on. Glad you caught the carbon and cleaned it up. Hope you also cleared up the surging issue. 

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Tuneup

I admire you and that 20. I was able to find a 16 after looking but was hoping to locate the stronger Eaton. The 7 is strong at least. It'll take a couple of weeks of care to get this one back and running and then I can check the surge. Again, no oil filter on the 16s. It does have the pressure sensor where it should be. The hole is there for the filter and was, of course, uncovered. I can't get that tin off unless I bend it or remove the main frame bracket. Then I found the engine itself is loose and there's an oil leak which appears to be a loose drain. I'm just going to pull it. I didn't build a workbench to sit around empty! I may even take pics which is something for me. Good luck with that 520!

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Chestnut

The Onan is pretty new to me as well I'm the lucky "owner" of not one but two 520's. My father in law left one with the kwik way loader. That's the one with the carb issue. I was looking for a snowblower to add to it and found a whole new tractor with snowblower attached. The one I bought just had the carb cleaned and it runs like a bear. I can't wait to get the "old" one starting and running the same way. I was just talking to a friend and he said he has a neighbor with eight wheel horse tractors, each with a different attachment. Apparently the neighbor doesn't like to change attachments. I'm not quite there yet. Four tractors at my mother in law's (two Toro Wheel horse), one tractor at my house, one walk behind snowblower, and a walk behind mower for each of us. Takes a while to change the oil and get them all running in the spring. Pictures of the two 520-H's on my intro post on the main wheel horse tractor topic.

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