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The following comes from a Technical Article I wrote for Mytractorforum several years ago. This article was written with the help of Boomer from Boomers Onan (he is a great resource for both parts and knowledge).


Flyball Spacer Replacement Kit
Onan P and B Series


Below is written instructions and a series of videos I have made on the topic. If you have questions drop me an email, if you need parts I am sure Boomer at Boomers Onan can help you out. 

Symptoms and Explanation:
- Engine will increase in RPM once it has warmed up. Typically after 20-45 minutes of operation.     Max engine RPM (depending on manufacture) is 3,450 to 3,600 RPM
- The governor on these engines is part of the cam shaft gear assembly. Attached to the cam shaft gear is a flyball spacer, with 5 ball bearings. As the engine RPM’s increase these bearings spin outward due to centrifugal force and press on the governor linkage that comes out of the top of the timing cover connected to the throttle controlling the RPM’s.
- Once an engine gets hot the flyball spacer will start to spin on the camshaft gear. The engine then loses the ability to properly regulate RPM’s and the engine can over speed.
- Most options to fix this problem involve removal on the camshaft. This fix does not require the removal of the camshaft and total working time is about 3 hours and a 24 hour set time. Not including removal and re-installation of the engine.


Supplies Needed:
- 1 metal early model flyball spacer (these can be sourced from Boomer)
- 1 timing cover gasket
- Red loctite
- 5/16, 3/8, 1/2, 9/16, and 5/8 inch sockets, wrenches, and associated ratchets
- Torque wrench

- Rubber Mallet
- Bar puller
- Alcohol to clean the camshaft mounting surface
- Bags for parts.

1. Drain engine oil, leave the filter installed
2. Remove engine from machine per manufacturers direction
3. Place the engine on a table where it can be accessed from all sides.
4. Remove only the rear flywheel cover. This will also include the coil since it is attached to the cover.
5. Remove the flywheel using the bar puller and the 9/16 socket with a ½ inch drive as well as a 5/8 socket on a second ½ inch drive. Loosen the flywheel bolt, leaving the bolt in and use the puller to loosen the flywheel. (you can rent a puller from most local auto parts stores if needed)

6. Once the flywheel is removed, remove the stator, the ignition module, and the timing wheel on the crankshaft. You will need a 5/16 socket for this. Put the parts in a plastic bag for safe keeping

7. Remove the timing cover bolts (4) and top nut (1). You will need the ½ socket for this. Carefully remove the timing cover. Do not use a screwdriver to pry off cover, this might damage the gasket surface and cause leaks. Using a rubber mallet; tap the cover until it is loose enough to remove by hand.

8. After the timing cover has been removed you will need to remove the C-clip holding the governor cup onto the camshaft. Be VERY CAREFUL NOT to lose the ball bearings or the C-clip. A small screwdriver can be used to remove the C-clip on the end of the cam shaft. It is helpful to place a block of wood under the front (flywheel side) of the engine to tilt the engine backwards, this will keep the ball bearings in place while removing the governor cup. Check the cup for excessive wear and replace if necessary.

9. To remove the old flyball spacer, use your fingers and gently rock it back and forth until it comes off. This may take a little effort. the inside of your spacer may look like this.

10. Thoroughly clean the mounting surface of the cam shaft. Denatured alcohol works the best. Apply to a rag and wipe until the rag is no longer dirty when starting with a clean section.

11. Check the fit of your new metal flyball spacer. Make sure to do this WITHOUT any loctite. Simply putting the flyball spacer on the cam gear will suffice, DO NOT tap it onto the gear at this point or it will be difficult to remove.

12. Apply the red loctite to the mounting surface. DO NOT APPLY AN EXCESSIVE AMOUNT, if this occurs red loctite will seep from underneath the flyball spacer and may end up in undesired locations. You can use your finger to spread the loctite.

13. Fit the flyball spacer on as best you can with your hands, then use a small rubber mallet to tap into place.

14. Let this sit overnight. In the mean time clean the gasket surfaces.
15. After cleaning the gasket surfaces put the new gasket on.

16. Place the ball bearing back into the flyball spacer, once again a block of wood under the engine to tilt it backwards will help. Be sure to EVENLY space the ball bearings. Failure to even place the ball bearings will result in an engine that will have a much shorter and shaker life than others. 

17. After the ball bearings have been replaced you can replace the governor cup. Then replace the C-clip.

18. The next step is to replace the timing cover. READ CAREFULLY. In order for the governor to work correctly the timing cover pin must be aligned with the governor cup. The governor cup will need to be turned until the hole with the plastic bushing is at the 3 o’clock position. Once the cover is on this can be tested by carefully tilting the engine towards you and testing the governor shaft for resistance. If there is no resistance remove the timing cover and try again.

19. The stator, and ignition if equipped can be reassembled followed by the flywheel. Be sure to torque the flywheel bolt to 55 ft lbs. Improperly torque flywheels can result in flywheel key shearing and cracked flywheels. Replace the engine shrouds and reinstall the engine.

Different Styles of Flyball Spacers found in John Deere Onan powered machines.

Flyball Spacer Fix Parts 1-4

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