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Discussion Starter · #1 ·
I have a 1990 JD 420 with an Onan P220G Spec C engine. I haven't had this tractor long and took it apart to fix a few mechanical issues and it has turned into a full restoration. So I pulled the heads, intake, exhaust to decarbon and adjust the valves. I also decided to pull the engine and replace the crank seal (flywheel side), the cam cover gasket and the oil filter housing gasket. I took the cam cover off to replace the crank seal and gasket and decided to take a look at the flyball spacer. My question is how do I know if the flyball spacer is ok or not?
 

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It’s good that you are servicing that engine, thoroughly cleaning and degreasing and fixing oil leaks. It will run cooler and hopefully last a very long time. Adjust the valves when you reassemble and consider resealing the intake manifold (seal inside the two halves) before you reinstall it. Over time the manifolds develop leaks and will let unfiltered air enter the engine after the carburetor, causing an improper air/fuel mix, poor idle and overall poor performance.
Keep all the tins in place and purchase a sealing gasket to seal around the oil filter if yours is missing or loose fitting. These steps are important to keep the engine cool.

Your flyball spacer looks OK for now but that composite material splits and allows the spacer to slip on the shaft. This causes the engine governor to work erratically and causes the engine speed to surge. You’ve done the major work removing the engine from the tractor and taking it apart. I suggest while it is apart you replace that flyball spacer with a metal one that won’t split.

I also suggest you replace the ignition module, the insulator behind it and the trigger module while the engine is dis-assembled. They fail over time and are simple to replace while the flywheel is already off.

Search this site for failed flyball governor photos and ignition module replacement for tips to follow for successful repairs.
 

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You should be able to source a metal flyball spacer from Boomer in Minnesota. Check out boomersonanparts.com He can also give you general advice about the engine and performing this repair.

The seal where the dipstick enters the oil pan can also be a source of oil leaks. Now is a good time to replace yours if it's leaking.

Other good preventative repairs to consider on your 420:

1. Replace the ignition switch if it is original. Over time they wear and connections become weak. If the switch looks and tests OK, consider adding a "Starter Improvement Relay" as an upgrade. You do not need to source the kit from Deere if you are handy with electrical systems and can source a simple 12V automotive style relay. Search this site for details.

2. Depending on the serial number/age of your 420, it may have glass fuses and plastic fuse cartridge holders. Over time the springs and plastic gets weak allowing poor electrical connections. If your tractor has glass fuses, consider replacing with blade type fuses and fuse holders.
 

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ITA47,

The spacer can loosen and spin relative to the gear even if it does not split or crack...but since you have a later version of the gear itself with the notch in the rim, there is a simple way to ensure the spacer does not spin by adding a "pawl' in one of the unused spacer cells. Just make sure it is either grooved or thin enough to let the governor cover rest all the way down to its original position when not being lifted by the fly-balls. Here is a good picture of the possibilities:
Automotive tire Light Bicycle part Wheel Rim


The middle solution can be done without any further engine disassembly...

Chuck
 

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Chuck, what kind of plastic would have to be used for these mods? I have had issues with the spacer slipping and spinning, on various Onan engines. My go to repair has been the metal flyball spacer, but I might have to try the pawl approach.
 

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Any nylon or delrin material should do it...not much mechanical stress on the part, and it just has to be able to survive engine temperatures. I would think even wood would work -- but a nonporous material is better... ;)

Chuck
 

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Discussion Starter · #7 ·
So if I wanted to make a plastic pawl would I have to turn my flyball spacer on the cam so it would line up with the notch, because right now my flyball spacer doesn't line up correctly?

If I go with the metal flyball spacer with the extended tab what do those usually cost?

Can a guy get the plastic flyball spacer with the extended tab? If so what is the part number?

Last does anyone sell the little plastic pawl?
 

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ITA47,
I have never seen a source for the plastic pawl or a listing of a common polymer that should tolerate an extreme temperature of say 250 F. Instead, I make an aluminum tab and anchor it with a screw (cemented in place). The third picture above is from onan p218g flyball spacer. It is nice to have the camshaft removed from the engine, but I have done these with the camshaft in place, rotated so a cardboard shield and magnet retains the drillings and tappings. Although I cannot claim that this will work for every plastic flyball spacer, heating it gently with a hair dryer has allowed a small rotation or removal for those I have tried.
Harold
 

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I also suggest you replace the ignition module said:
Agree with Mike on this. You ought to seriously consider replacing those things before reassembly. With age, use, can become unreliable and can\may cause the engine to shut down when hot and not restart until all has cooled sufficiently.

Product Organism Font Line Slope
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Harold,

Clearly the plastic the spacer is made from is meant to be used at these engine temperatures. Most high temp plastics will retain all their physical properties to well over 400 degrees F -- see this link;
Of course if you used a bit thicker aluminum part with the same shape & groove as the plastic one shown, no drilling would be needed. Your technique to capture all the metal shavings seems like it would work well also.

ITA47 -- I don't know of any commercial source of the added plastic pawls either...all the ones I have seen have been shop made by the owner of the tractor. The plastic spacer with the extended "finger" is a factory part from Cummins/Onan, but only as an assembly with the gear itself. It seems to be no longer available...
Bicycle part Rim Auto part Gear Circle


...and Bo and Mike are right about preemptively dealing with any electronic ignition issues while the engine is out.

Chuck
 

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Discussion Starter · #11 ·
Thanks guys for all the feedback and advice. I am in contact with Boomer and I am going to purchase the aluminum extended tab flyball spacer from him. I understand what you guys are saying on the ignition items, the problem is I'm already over budget on this thing. If they were cheap enough I would change them but the ignition module under the crank is $150 from Cummins. I'm going to test the ignition items if I can that you guys mentioned and run them if they check out ok. I'm hopeful with them cleaned up they will run cooler and continue working. Worst case is I will have to pull the engine again to change them sometime in the future. I do appreciate the suggestion though.
 

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Anyone who has dealt with repairing, refurbishing, rehabbing, restoring older used equipment is well aware of the components, parts costs, and sometimes the unavailability of wanted things. [Remember the commercial: "pay me now, pay me later"?] Plain dang cool, neat - what you've posted\done so far. Think we all love to see it and wish you the best of luck.


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Discussion Starter · #13 ·
Mike_U suggested Boomer in Minnesota, so I gave Boomer a call. What a wealth of knowledge on the Onan engines. I decided to get the CNC machined flyball spacer from him as well as an oil pump rebuild kit, crank seal and cam cover gasket. When the parts get here I will get this thing back together. I also have a new oil filter mount gasket and dipstick seal. Hopefully that will take care of the oil leaks. Thanks everyone for all the advice, I do appreciate it.
 

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Discussion Starter · #16 · (Edited)
I had some time this weekend so I worked on the engine. I got the new aluminum flyball spacer installed that I got from Boomer. I also installed the new crank seal in the timing cover and timing cover gasket. I also installed the oil pump gasket and oil filter adapter gasket. Earlier I had already installed the new oil filler tube seal. Hopefully all this will take care of my oil leaks. I also started cleaning everything up, it's looking better. The installation of the flyball spacer was pretty easy. I removed the plastic one and it broke during removal. I then cleaned the cam gear good with lacquer thinner, put a thin bead of red loctite on the inside of the spacer and tapped gently it onto the cam gear with a plastic hammer. If you are needing a flyball spacer or any other Onan parts give a shout to Boomer, he can fix you up. Boomer's Used Onan Engine Parts
 

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Me too! And an interesting guy. Some younger guys have been insulted by his no bs type of attitude. Be direct about parts inquiries and he’ll elaborate at length to help you, be wishy washy about not knowing why your JD is acting funny and he’ll tell you as soon as he loses interest he’s hanging up the phone! 🤣
 
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