Military Mule tune up procedures

[Tim Hoskins]

Hello,
I am helping a friend get his military mule running. He has had this thing for over 10 years. The guy he bought it from said it only needed to be timed and it would run. My friend never got around to getting it running. This machine has an opposing 2 cylinder Hupp air cooled engine with a magneto ignition. I called Hercules engine division and they could not provide me anything other than it was manufactured between 1966 and 1969.


The id plate identifies the following.
Ord Ser No: V- 001802
Ord Part No: 10919400.
Model No: AO-42
Contract No: DA-23-195-AMC-909 T
Rated RPM: 3600
Full Advance: 18 degrees BTC
Spark Static: 0 degrees TDC

I have timed VW engines using the static light so this is not a mystery to me.


I have a series of military manuals for this machine however none of them identify the following:

1. Location of the points: I suspect they are inside the magneto cover but I would like to know for sure before I begin exploratory.
2. Point gap:
3. Which cylinder is #1? Looking from behind the vehicle is it on the left or right?
4. Valve adjustment: What is the gap for intake and exhaust valves?
5. Battery voltage/polarity: I suspect it is 12 volt negative ground but I would like to be certain.

Once I get this running my friend will want to sell it. Does anyone know what these are worth?

Any help would be greatly appreciated.

 

[mulman7]

Points are inside the magneto. the points are set at 0.016


Before you pull the mag pull the governor and rotate the engine CCW so not to impulse the mag and it fire accidentally. initial timing is done with the governor removed so you can align the mag and cam gear.
locate the V on the mag gear and notice if it is matched with the V on the cam gear since it is a V model engine and not a KM.

When the two gears are aligned the roll pin on the mag gear will be at 9 o'clock.

Install the governor and verify that the heim joints on the connecting rod governor to carb are loose otherwise the carb will not open properly.

Running speed the timing is 18 degrees advanced.

If I remember correctly #2 is the blower side but it makes no difference since both plugs fire each revolution. One on compression and the other on exhaust stroke then it switches. The mag fires like the old Harley. The top ignition cable runs to the blower side due to ease of connection not timing order.

No valve adjustment needed they are hydraulic.

Electric start mules use negative ground.

Do not put 12 volts to the condenser connection on the magneto as it is self contained and does not use outside voltage to operate.

 

[Tim Hoskins]

Thank you for the info. Will be attempting to get this thing to run tonight. Any idea of what these sell for? My friend will want to sell it once it is running. I believe he is on to other interests now.

 

[swiss]

Awesome detail in this post. Great Job Mulman!!!

Points are inside the magneto. the points are set at 0.016


Before you pull the mag pull the governor and rotate the engine CCW so not to impulse the mag and it fire accidentally. initial timing is done with the governor removed so you can align the mag and cam gear.
locate the V on the mag gear and notice if it is matched with the V on the cam gear since it is a V model engine and not a KM.

When the two gears are aligned the roll pin on the mag gear will be at 9 o'clock.

Install the governor and verify that the heim joints on the connecting rod governor to carb are loose otherwise the carb will not open properly.

Running speed the timing is 18 degrees advanced.

If I remember correctly #1 is behind the blower but it makes no difference since both plugs fire each revolution. One on compression and the other on exhaust stroke then it switches. The mag fires like the old Harley. The top ignition cable runs to the blower side due to ease of connection not timing order.

No valve adjustment needed they are hydraulic.

Electric start mules use negative ground.

Do not put 12 volts to the condenser connection on the magneto as it is self contained and does not use outside voltage to operate.

 

[Tim Hoskins]

Mulman,
Thanks for the great instructions. I got the timing down but I cannot get spark. I see that the condenser was hooked up to 12v pos. Can you tell me if this could have ruined the condenser or mag? It appears that that this wire should be connected to the mag terminal on the key where the key connects it to ground when turned off killing any spark. Please confirm. Are there any other adjustments within the mag that might fix my non spark issue?

Best regards

 

[mulman7]

Pull the magneto from the engine and put it in a vise. Remove the top [4 screws].

Disconnect the condenser wire from the points and reattach the coil lead to the points.

Make sure the points are clean and bright [400-600 grit wet-dry sandpaper] then contact spray to make sure the points are clean.
Set to 0.016"

Impulse the mag and watch for a bright spark across the points.

If no spark then you have a bad coil.

Attach the top but do not connect the condenser.

Attach your ignition cables and hold the ends about 1/2" to 1" apart and impulses the mag you should see a bright spark.

Short one cable to the mag and the other 1/2" to 1" from the mag and impulse then reverse. If both cables show a bright spark you have a working mag.

If one wire will not fire reverse the wires attached to the mag and try again. If no spark follows the wire then you have a bad cable.

If no spark follows the mag connection then you have a bad bakelite tower top.

Pull top and connect condenser. Install top and check spark to ignition cables.

If no spark then you have a bad condenser.

Contact me for a new magneto and or parts or John Emery for mag parts. Saturn Surplus sells a mag rebuild kit for the 2AO42 engine but it does not have the water proof condenser used with the mule magneto it will work [Fairbanks Morse not Wico]

 

[Tim Hoskins]

Fortunately I only changed the points and condenser and I now have spark. Unfortunately we were not able to get it to start before the battery died. Pulled the spark plug and dry as a bone. Working the fuel portion now. Will keep you posted sir.

 

[The Auto Shop teacher]

Tim, on my own mule with electric start I didn't have a good ground connection on my ignition switch and fried my points one time, so check your electrical connections.

 

[Tim Hoskins]

My starter is now slipping. Not grinding. I am guessing that there is a clutch on the reduction gear. Anybody out there know how to diagnose or fix this?

 

[mulman7]

Upload a pic of the starter. There has been 4 ways to convert the mule to electric start using the starter mount on the engine bell housing.
Remove the starter and connect to a battery and energize to observe if the bendix moves out and turns.

1-Ford starter machined into the original manual starter
2-VW starter converted
3-Reduction gear starter
4-Prestolite starter used with the Fort Campbell A5 conversions

Starters 1 and 4 should be a spring loaded bendix.
Starter 2 is a solenoid activated bendix.
Starte 3 not sure. I will have to pull one and check.

Most Starter / Generator shops can repair especially the ones that use a solenoid activated bendix i.e. VW

Starter 1 in my experience failed the most due to the torque shearing roll pins securing the gear to the starter shaft and the pin for the bendix.
I have 3 and 4 in stock if you need one.