Weekend Freedom Machines banner

Need JD 420 Garden tractor help:

4045 Views 44 Replies 10 Participants Last post by  billy_cravens
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!!
See less See more
1 - 9 of 45 Posts
I agree with Dave, You need to run a compression test
The Onans are known for loosing valve seats. When that happens the valve seat rides up and down with the valve, seating and unseating itself until it finally beats the block bad enough that the seat wont sit in it properly at all.
It depends on several things
how long its been loose & how much damage is done to the block
I opted to replace my block with another block.
A good machine shop can fix most but not all.

BTW Onan sells an over sized valve seat for them.

Mine did exactly what yours is doing. not running right and low on power and sputtering out of the carb. The most common valve seat to go is the right side intake seat

Know that there are a few things that can be done to prevent the issue.
Forum member JRL sells a replacement heat shield that seals off the engine to the firewall and improves fresh air flow to the engine.
Onan also sells a rubber grommet that seals the oil filter opening in the engine shroud to force good airflow to the right side of the engine.
See less See more
stuck valve
bad valve seat
hole in piston
broke rod

most likely a stuck valve or bad valve seat
you remove the head and then the valve
look for carbon on the valve stem
Also check for a loose or bad valve seat

try page 44 of the Onan manual
It is the step by step process
I use a standard Automotive C-Clamp style valve spring tool. It works well and has enough adjustment.

If you take the block all the way down to bare block you will need a puller for the crank gear. It's an unusual small thread and takes an unusual bolt. I ordered the bolts from my JD dealer and used them with the puller I already had.

For reassembly you will need a torque wrench that reads inch pounds or one that reads FT-LBS in single digits and they are hard to come by

The rest are standard hand tools
1) you need to remove both. If you use a machine shop they will want just the bare block

2) it depends on the amount of damage done to the block by the pounding of the loose valve seat
I took mine to my machine shop and let them look at it. They would have done the repair but I was able to come up with a good block at a decent price and just replaced the block rather than fix it.

if you look at mine the block looks melted and the the seat base is beat back probably too far to repair.

See less See more
It depends
A lot of us cut the front of the bolt holes out making Two slots on the muffler bracket
If this hasn't been done to yours then yes you will need to remove the PTO

We have a winner!

Strip it, send it out, and fix it right.
You have caught on to several of these, but I'm going to post them all for you

1) Make sure you have the insulation sheet that goes on the firewall. This forces air flow through flywheel screen and under the engine shrouds

2) Use the Onan oil filter seal. It closes off a potential leak area between the filter and the sheet metal. This is why the side with the oil filter is the most common to fail

3) keep the cooling fins clean. I now use air pressure to blow the dirt and dust out of them

4) Keep the Belly Pan on. This slows down the amount of dirt and debris sucked in through the flywheel

5) don't use gas with ethanol (ethanol cause problems with fuel lines and carb, potentially leaning the mixture)

All things learned from reading this site and going through this very same problem
See less See more
1 - 9 of 45 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.