520 Acts like it chocks itself out

[S416-8 388]

Going through the new to me 520. So far I've replaced the spark plus and wires, fuel and air filter, pre-cleaner, fluids are clean and at the right levels BUT the issue is that it runs great for several mins and then acts like it chocks itself out. Let it sit for 5 or so and it runs again but repeats after maybe 5-10 min. I dumped and changed the gas as well... 

 

Forgot to say that it is a 1992 tractor. 

 

I can tear tons of things apart but carbs seem to be my issue.. never go right .. think that the carb may need to be cleaned and redone.... and ideas?? 

[c-series don 9,980]

Try running it with the gas cap loose, perhaps the vent is clogged. Just a guess. If not, you may have to pull the carb and clean it? 

[S416-8 388]

thanks thinking the carb,, has no gas cap just ordered a new one until then it has a shop towel over it to keep everything clean. Guess it is time to check out puling the carb..

[8ntruck 7,815]

Is there a strainer on the fuel line fitting inside the gas tank?  That might be clogged.  Try blowing some air into the gas tank from the fuel line?

Edited June 10, 2023 by 8ntruck

[lynnmor 7,809]

The ignition module behind the flywheel can fail when the engine heats up, then operate again after cooling.  Check for spark immediately after the engine stops.  Since it seems to be heat related, have you cleaned the cooling fins on the cylinders and under the engine?  Is the rubber gasket around the oil filter?

[S416-8 388]

Thanks guys for the info.. have used the compressor to blow out as much dirt that I could around the engine but have taken off the covers to give everything a really good cleaning. Will try the air in the fuel line and spark plug check today as well... 

[S416-8 388]

Deep into it now. No spark when it died so decided to go through it all no turning back now  

[lynnmor 7,809]

You should have checked the compression before pulling the engine.  Did you follow the Onan manual in regards to testing the coil?  Unless there is a wiring, ignition switch or safety switch issue, the usual problem is the coil or ignition module.

 

Now that you pulled the engine, I suggest pulling the heads to remove carbon and inspect the cylinders.  If it were mine I would freshen up the valves and seats along with any fuel system work you might need.

 

Don’t get so far ahead of us, we are old and slow.

[S416-8 388]

Oops. No spark so thought ignition. The thing under the covers was filthy and caked with gunk. So figured might as well go through everything. 
 

fuel system checked out. Pump and gas flow out of the filter was strong and steady. So moved to electric. Died in about 5 mins. Pulled a plug and checked for spark none. So….  

[S416-8 388]

Even if I have to put it back in to fully test it before doing anything else I am happy that I did this. Pulled the flywheel and it was caked under it including all the electronic things under there. Blew out everything, tomorrow I will cover and seal all the holes and give it a good cleaning. Also found 3 of the head bolts were loose slightly 1/2 turn or so. Gotta find the instructions on how to "pulling the heads to remove carbon and inspect the cylinders." as suggested.

 

On the tractor side, again dirty as can be. Couldn't even see relays it was built up so bad. That will also get cleaned tomorrow as well. The engine mounting plate as that was loose and several other things to take care of. 

[S416-8 388]

Cleaned a ton of crap off the engine and pulled 1 side cover and after a spraying a cloth with carb cleaner and wiping things for a few mins this is what I have. 

[S416-8 388]

Will be testing the part tomorrow using this test

[lynnmor 7,809]

The black on and around the intake valve suggests that new valve seals are needed.  Use new head gaskets when you reassemble.  The heads should be lapped to make them flat, ask if you need to know how.  I have used oven cleaner to clean heads, just don’t use it on the block or piston.  It would be a good idea to run a tap in the bolt holes, then blow them out.  I bottom tap the manifold and exhaust bolt holes and use bolts one size longer where possible because they are easy to strip.  Onan says to put a drop of oil on all the bolt threads.  Use a torque wrench and don’t go over specification.

 

The ignition module should have a gasket behind it to help shield it from heat, your earlier model didn’t have one but you should add that.  You likely found that many bolts are corroded fast, spray penetrating oil on any and all fasteners and repeat every chance you get.  Those small bolts holding the module and stator are easy to twist off.

[lynnmor 7,809]

Just now, S416-8 said:

Will be testing the part tomorrow using this test

Remember that it may very well test fine but fail at high temperatures.

[S416-8 388]

2 minutes ago, lynnmor said:

The black on and around the intake valve suggests that new valve seals are needed.  Use new head gaskets when you reassemble.  The heads should be lapped to make them flat, ask if you need to know how.  I have used oven cleaner to clean heads, just don’t use it on the block or piston.  It would be a good idea to run a tap in the bolt holes, then blow them out.  I bottom tap the manifold and exhaust bolt holes and use bolts one size longer where possible because they are easy to strip.  Onan says to put a drop of oil on all the bolt threads.  Use a torque wrench and don’t go over specification.

 

The ignition module should have a gasket behind it to help shield it from heat, your earlier model didn’t have one but you should add that.  You likely found that many bolts are corroded fast, spray penetrating oil on any and all fasteners and repeat every chance you get.  Those small bolts holding the module and stator are easy to twist off.

ok now I am a bit lost.. I've never done any of this so will need some help.. didn't see any gasket so I guess I will need to add that to the parts list...  I guess valve seals, head gaskets, and the gasket for the ignition coil can be found at the vendors...

[S416-8 388]

ok.. grr what did I get myself into on this one... 

[lynnmor 7,809]

3 minutes ago, S416-8 said:

ok.. grr what did I get myself into on this one... 

Actually most of what you are doing is specified maintenance, of course few do it and blame the engine manufacturer for their problems.  If you take your time and do all of the items we talk about, you should have a reliable engine for years to come.

 

You can see the "gasket" we talked about here.  You will also see the ignition module and get an idea what they cost.  You might want to make a list of part numbers then search for best prices on new and used parts.

[S416-8 388]

Will follow what you advise. May I can have some things follow me home from the show as well.... I see some of the parts are well expensive as well so .....

[lynnmor 7,809]

31 minutes ago, S416-8 said:

Will follow what you advise. May I can have some things follow me home from the show as well.... I see some of the parts are well expensive as well so .....

Onan parts are now beginning to get scarce, they stopped producing many items so already high prices are getting crazy.  Make a good shopping list for the show, try to get there early and do your shopping before entertaining yourself because rare parts go fast..  I may not go this year for a variety of reasons.

[S416-8 388]

Would you be replacing those vales along with the valve seals? I am not sure if it is carbon yet but the surface is textured. So far I am checking to make sure the following parts are correct to put on the list:

 

Valve seals

maybe the 2 valves

Head gaskets

Rubber gasket for around the oil filter

Found this kit, sold out but looking for the individual parts: https://onanparts.com/index.php?main_page=product_info&products_id=737

166-0785 Ignition Module
166-0767 Electronic Ignition Rotor
166-0786 Ignition Module Insulator
312-0256 Condenser. Connects to  +  side of coil

 

This gasket kit  https://onanparts.com/index.php?main_page=product_info&cPath=1_7_19&products_id=18

Onan 168-0189 Valve Grind/Carbon Removal Gasket Set P Series

Two 110-3181 Head Gaskets:
Two 154-2495 Intake Gaskets:
Two 154-2746 Exhaust Gaskets:
Three 110-3709 Valve Cover Gaskets.

 

Then of course I am still waiting to lean what this requires "The heads should be lapped to make them flat, ask if you need to know how"

[lynnmor 7,809]

First thing, check the condition of your fuse block, especially the bottom.  Here is one source of the Dorman 85668, prices vary so shop around.

 

Valves can be ground by any automotive machine shop, they don't need replaced unless they are cracked, warped or the stems worn.  I use a Neway valve seat kit to resurface the seats and restore the width of those seats, again some automotive machine shops can do that for you.

 

The ignition module is the prime suspect here but with anything electrical there may be some other intermittent issue, for example the ignition switch, the fuse block, safety switches,  the 9 pin connector or the coil.  That 9 pin connector is a problem for many later model Wheel Horses.  You got way ahead of of us by pulling the engine before doing a number of tests.  One thing that should have been done was to run a jumper wire from battery plus to the coil plus to see if the engine continued to run.  The temperature rise and then fail led me towards the module.  Call A-Z Tractor and see if he has a module and can bring it to the show for you.

 

The gray 166-0767 rotor rarely fails, if it is black replace it.  You might want a flywheel key if yours isn't perfect.

 

I have never replaced a condenser.

 

You will need all of the gaskets that you mentioned plus the one under the carburetor.

 

Here is a video showing the truing of a head.  If you have a known flat surface the glass isn't necessary, I use the table on a high quality vertical bandsaw that I checked for flatness.  Contrary to popular opinion, glass isn't perfect and it can bend a bit.  The video shows using 400 grit paper, I use 320 because you don't need that fine finish and 400 takes forever.

 

While the engine is apart, consider glass beading the exhaust and painting it with Rustoleum High Temperature paint.  Also, paint the valve covers, the heat shields and the engine tins.  Test the intake manifold for leaks and examine it for cuts in the edge from the heat shields.

[S416-8 388]

4 hours ago, lynnmor said:

Thanks

Fuse block:  The main Furse was bypassed with a weather proof one. Have a new fuse block and cover ordered from Wheel Horse Parts & More - did this before I started this discussion. 

 

Values look ok just need a good cleaning. I've been watching videos on using a suction value tool and compound to resurface the values. As this will probably be the only time I will do this would this method work?

 

The ignition module is the prime suspect here but with anything electrical there may be some other intermittent issue, for example the ignition switch, the fuse block, safety switches,  the 9 pin connector or the coil.  That 9 pin connector is a problem for many later model Wheel Horses.  You got way ahead of of us by pulling the engine before doing a number of tests.  One thing that should have been done was to run a jumper wire from battery plus to the coil plus to see if the engine continued to run.  The temperature rise and then fail led me towards the module.   

 

 

I jumped on the engine when I saw all the grime built up on everything. Knew I would be doing this asap but never realized that there was more testing to be done.

Checked everything over and outside of the fuse block everything else looks good. Will spend the time to clean every connector and add some dielectric to them.

 

Call A-Z Tractor and see if he has a module and can bring it to the show for you. Will do thanks.

 

The gray 166-0767 rotor and fly wheel look fine - so should be good there.

 

I have never replaced a condenser. Ok thanks will just leave that one. 

 

You will need all of the gaskets that you mentioned plus the one under the carburetor. Ok thanks

 

Here is a video showing the truing of a head.  If you have a known flat surface the glass isn't necessary, I use the table on a high quality vertical bandsaw that I checked for flatness.  Contrary to popular opinion, glass isn't perfect and it can bend a bit.  The video shows using 400 grit paper, I use 320 because you don't need that fine finish and 400 takes forever.       I saw a different video but this was great.. I have a few heavy floor times that I checked with straight edges that have no warp on contours in them.. Will check them out again tonight using a flashlight looking for light the gets under the edges ...

 

While the engine is apart, consider glass beading the exhaust and painting it with Rustoleum High Temperature paint.  Also, paint the valve covers, the heat shields and the engine tins.  Test the intake manifold for leaks and examine it for cuts in the edge from the heat shields.

Ok might as well seeing I have it all apart .. Are we having fun yet...

 

The other thing that I found is that when I pulled the valve cover the gasket was not set correctly. On edge was sitting on that slightly lifted edge on top of the valve. So get to make it right at least

 

Edited June 11, 2023 by S416-8

[lynnmor 7,809]

 

Lapping valves is something I gave up a long time ago.  Grinding the valves to the correct angle and cutting the seats is the correct way.  Here is the theory; lapping will make the already too large contact area even larger.  The increased contact equates to less pounds per square inch and that can cause a leak that will burn the valve.  Too small of a contact area will not allow enough heat to escape the valve when it is closed.  Many on here use the lapping method, I am not one of them.

 

When you remove the valves, be sure to have all holes blocked so the keepers and dirt don't fall in.  Before doing anything in that area remember that a shop vac is your friend.

 

Good mufflers are getting hard to find and even those in only fair condition are bring big money, that is why you want to do everything you can to preserve yours.

[S416-8 388]

Sounds good thanks.. so lapping or not to lap that is the question? I guess? If I clean everything extremely well, new gaskets etc.. is that what you would be doing? 

 

I have the vac with my and air gun and cleaner so hope all works there....

[lynnmor 7,809]

2 hours ago, S416-8 said:

Sounds good thanks.. so lapping or not to lap that is the question? I guess? If I clean everything extremely well, new gaskets etc.. is that what you would be doing? 

 

I have the vac with my and air gun and cleaner so hope all works there....

Again, I am a no lap kind of a guy.  I said in a previous post that I use a Newway cutter to do the seats, I didn’t tell you that I have a tool & die shop and can grind the valves myself.  I have had low compression readings with valves that appeared rather good and freshening up the valves and seats things went back to normal.

 

I use a wire wheel to clean all of the deposits off the valves.  Do you have the ability to remove the valves?  You will need some kind of spring compressor.  Look thru the Onan Service Manual for lots of information, I hope you downloaded it.