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Need JD 420 Garden tractor help:

3984 Views 44 Replies 10 Participants Last post by  billy_cravens, 
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Has Onan 218 (instead of Onan 220) and was running great for several years until tractor just stopped one day a few weeks ago after 30 minutes cutting grass. Would only restart after sitting for a while. When restarted the tractor was running somewhat roughly and the RPMs were very low. Changed oil and filter, replaced spark plugs and wires, new air and fuel filters. Still runs as before with RPMs not near where they should be and are very low. And as before, I can run the tractor for a while, shut it down, but it will not start back up until it has cooled again. What approach should I take to troubleshooting? Should I be looking for vacuum leaks, carb problems or governor/throttle adjustments? I have a 420 service manual as well as the Onan engine manual, but I am looking for advice on the best area to start investigating. I've already had to have someone else cut grass for me once
and I've got some dirt to move!

...and thanks Dave T. for pointing me in the right place to post this!!
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Dominic, thanks for the welcoming! As Dave T pointed out, the Onan is the P-218 and it therefore has electronic ignition. I will definitely change the fuel lines, couldn't hurt since I do not know their age and I have read about cracks that can cause vacuum leaks.

Dave, how do I test the ignition coil pickup behind the flywheel? I couldn't find anything in the manuals unless I have overlooked it. I need to get my hands on a compression test kit and i will test for compression.

John, just in case, is a loose valve seat an easy fix?

A couple other observations...I have been getting a burst of black smoke upon start-up that quickly disappears. Also, I ran the engine without the air filter and I could see gas sputtering out of the carb (normal?). When shutting down I could see smoke hovering inside the carb.
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I am going to start with testing the coil while I wait to get my hands on a tool to do compression and leak down test. The Onan manual does not provide a diagram of testing the primary windings. I assume these are just the terminals on the coil next to where the spark plug wire holes are located?

"2. Place a black lead on negative (-) coil terminal and
red lead to positive (+) coil terminal. Primary
resistance should read between 2.90-3.60 ohms."

I am still wondering how to test the ignition coil pickup behind the flywheel if anyone has any advice how to do this.
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I tested the coil (part no. 166-0820) in my 80 degree garage last and it read 3.6 ohms for primary resistance and 21,800 ohms for secondary resistance. This is about 2,000 ohms above the range indicated as acceptable in the service manual. Is there any +/- variability in this reading? Is a new coil in order here?
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Hi Chuck, I have not tested the ignition module, but plan to do that later when I can get a helping hand. The tractor will start and run, just the same low RPM condition as stated earlier.

I wonder which model coil the Deere manual refers to. I think the earlier coils had their own bolts and then the newer style have the bracket. Supposedly the newer style coil will have a little higher resistance reading than indicated in the Onan manual, around the 21K ohm range, but that's no where near what the Deere manual states!
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Chuck, I have not checked valve clearances yet. Also, no compression or leak down test yet, that's on the books to do though. Wanted to go with the easier things first until I can get a tool for testing compression.
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Tested the ignition module this morning. Getting 12.46 volts and 0.9 volts. I assume this says the module is good?
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Finally got to testing compression. First cylinder tested at 110 psi. Second cylinder...0 psi. What possible scenarios am I looking at here?
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If it is a stuck valve, is there a good procedure to "unstick" an Onan P218 valve?
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Thank you everyone for all the help up to this point! I will be pulling the cylinder head this week to investigate the problem. Is there a specific kind of valve spring compressor tool that works best for the Onan P218? I have seen different styles available through various auto part stores loan-a-tool programs. Any other tools i may need when looking into this potential valve issue?
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I pulled the head tonight (oil filler tube side opposite the exhaust tip). Looks like the intake valve seat is quite loose and the valve will not seat properly. A few questions:

1) My valve spring removal tool should arrive tomorrow. Can I get the intake valve out without removing the carburetor and exhaust? Looks like there's enough room in there but I can't tell.

2) What are my options for dealing with the loose valve seat?
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Okay, looks like more work to do here then. I'll get a better look at both valve seats once I get the valves out. I might as well just pull the other head and have a look there as well. Won't hurt to decarbon since I'm in there anyway.
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I removed the exhaust "header" bolts. I see there looks like two bolts for the muffler bracket underneath the PTO clutch assembly. Is there an easier way to remove the exhaust or does the PTO clutch assembly have to be pulled?
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I guess I can loosen the bolts and see if this has been done. Not keeping my hopes up. I beginning to think I should just strip everything off the block at this point so I can get a good look and likely it's going to a machine shop.
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I think that's my new plan. It's always a krap shoot buying older equipment. The PO told me that they blew the original engine, then put the "late model" P218 in there suggesting the engine was not very old. The PO ran it for one summer and then it only lasted me 90 hours. I plan to have this machine for a very long time so I would like to know that the engine is working at its best potential.

I'm learning more and more about this machine as I read. I may have unknowingly contributed to its demise. It seems it's often debatable as to their worth, but my machine does not have a belly screen. Also, there doesn't appear to be any firewall insulation which I have read will help to direct cooling to the engine. I may look into getting the insulation while I have it torn down.
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Thanks, John. That's a huge help. I'll have to look into getting the filter seal too. I don't have a belly screen and have been trying to locate one. I'm not sure I can get around the ethanol issue though, unless there's a way to find gas stations that do not use any ethanol containing fuel. Thanks for the tips!
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Just found this website for finding ethanol free, pure gasoline.

http://pure-gas.org/
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Okay, so I am slowly working on removing the engine from this 420. Is it a good idea to remove the firewall? There's one last bolt holding it to the transmission cooler assembly. Should I remove the transmission cooler? It looks like it might also help to remove the battery tray and side tins next to the dashboard to make more room. Getting close, but looking for recommendations on making life easier.
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This is my first time and I was hoping to just make more room by removing the firewall, but I see your point, probably just making more work for myself, I'm good at that!!
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Thanks for the tips!! I hope the loose valve seat is the only problem.
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