AO42 Cam Replaced WO Pulling Engine

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Location: Georgia

AO42 Cam Replaced WO Pulling Engine

Post by muleman7 » Mon Oct 26, 2015 11:08 pm

Through my years of working with the Mules I have found 3 major weak links.
1 the Drive Gear in the DG Housing it will split at the keyway.
2 The Exhaust Seat will fall out when the Head over heats #1 cyl more frequently. Mice love that area for their nest.
3 The Front Cam Bearing will spin in the block and create more clearance allowing excess oil into the Timing Gear Chamber. The gears will whip the oil and it will be discharged through the Vent Valve into the Carburetor. This will cause the plugs to oil foul.
4? Yes the Later Style Tie Rod Ends wear quickly.

Spark Plugs that Oil Foul can be caused by:

1. Worn or Broken Piston Rings [not likely]
2. Excessive Intake Valve Stem Clearance or defective Valve Stem Seals [not likely]
3. Bad Fuel Pump Diaphragm [very likely]
check oil level if high and smells of fuel replace fuel pump and change oil and filter.
4. Bad Front Cam Bearing [likely]
check Vent Valve at air horn for excessive oil with engine running. Your finger will wet with oil quickly. I had a customer's mule that fouled new plugs within 5 minutes. A new Camshaft fixed the problem. When the bearing spins it reduces the Cam Bearing OD. The Engine Block's Bearing Bore ID is not effected. The surface of the Cam Bearing will show signs of concentric circular marks.


I will attempt to show you the process I use to replace the camshaft without pulling the engine.
Remove the:
Engine Guard
Fuel Line from the Sediment Bowl to Fuel Pump
Oil Filler Tube Bracket
Blower and Bracket
Valve Covers
Rocker Assys
Fuel Pump
Spark Plugs

[Spin the engine over several times to move the Lifters away from the Cam Shaft. this will aid in the removal and replacement of the Cam Shaft]

Pulley from the Crankshaft
Timing Gear Cover [I use a torch to heat the cover to release the gasket from the cover I do not like to scrap gaskets.
Baffle Diaphragm replace 1 bolt to hold the Diaphragm Assy
Rotate the Crankshaft until the DOT on the Crank Gear and Cam Gear line up and mark them with paint [White Finger Nail polish] This should give you access to the Cam Mounting Bolts remove the bolts.

CAUTION Carefully pull and rotate the Camshaft from the engine without ROTATING the Crankshaft.

Clean the Cam Bearing Bore in the block I put a small amount of Loctite on the outside surface of the Camshaft Bearing to prevent future failure. Future removal will require heat or you can pin the bearing.

Mark the new Camshaft Gear at the DOT [This will assist in lining up the gears when installing the new Cam]

You may decide to install a new Bearing on the one removed instead of a new camshaft. If you install a new camshaft coat the Bearing surfaces, Lifter and Fuel Pump Lobes with Sealed Power Camshaft Assy Lube from O'Reilly Auto Parts or equivalent. ... &ppt=C0139

CAREFULLY insert the Cam and line-up the teeth of both gears. Let the Cam Rotate as you push it in you may need to assist with a hammer handle lightly tapping. If the Crank Gear never moved then the Cam should slip into the Oil Pump Gear.

You now can reassemble the Engine and enjoy years of Mule-ing.

Engine stripped ready to remove Baffle


Mark Timing Teeth


Cam Removed


Ready to install a New Camshaft or New Bearing onto your Camshaft


VERY IMPORTANT check the Woodruff key and make sure it is lower at the insertion point so it does not hang on the Keyway of the Oil Pump Gear. If the Woodruff Key is loose use Loctite and a little heat to set it. You do not want this Key to fall out.


Cam Installed


Now reassemble the Engine

Leave the Fuel Pump loose to ease starting the Inverted Flare Fitting for the Fuel Line to the Carburetor. This can be tricky and I have used a long flat nosed screwdriver to help push the Flare Nut into the Fitting as I turn it. Do not Cross Thread as this is Brass on Brass.
Mules are my passion

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