Engine Page

Commonly know as a stove bolt six, these engines were virtually identical to the standard prewar engines. During the course of the war modifications such as improved air filtering on crankcase and generator were added to improve engine life.


Engine Details

Manufacturer........................................................General Motors
Type.......................................(216 cubic inch) 6 cylinder in line
Power.............................................................85 bhp at 3400 rpm
Torque........................................................170 ft.lbs at 1200 rpm
Electrical System....................................................battery 6 volts

The pictures are from the restoration of the Patter 13 3-ton in 1989, Pattern 12 3-ton 2001-2006 and from repairs along the way.

Click on blue border pictures to enlarge

Clink on blue text for more pictures

In 25 years of driving my CMPs I have found the engines and trucks to be very reliable. In that they have broken down on me only a very few. Never have the trucks failed to the point of having to be towed home. Break downs include the following :

Here you can see the simple design of the transmission. Four speeds forward one reverse, with straight cut gears which makes double clutching a requirement.

Top -The valve cover and side panel have just been removed from the engine no cleaning has taken place yet. Note that there is no sign of any sludge or dirt in the engine. This is one of the reasons that I believe the odometer reading of 6314 miles.



Bottom -The valve cover and side panel have just been removed no cleaning has taken place- but water coming from cracks are a bad omen of what is to be found. Again the mileage is low but the 8588.3 miles were hard miles


1942 Pattern 13 


1941 Pattern 12


In the bottom view you can see the detail of the connecting rod scoops or dippers. The engine was in very good condition, compression was good and even once I had check the condition of the inside I replaced the cover gaskets and put it back together to test run extensively. No smoke or oil leakage every thing looked so good I cleaned the outside of the engine in place and painted it. Before cocooning it in plastic and starting on the chassis.


Layers of paint and cosmoline covered many parts of the truck. As the cosmoline dried out it peeled the paint off with it. But the wear on mechanical parts, very little and the very low mileage on the odometer seemed to match.  The nose goes back on once the chassis has been sand blasted and painted and is going back together. BEAST lends a hand in moving heavy parts around.

 A 3-ton roadster quickly followed note the mix and match tires. But the first trip down the road was short for in the first 3 miles a quart of oil leaked past the rear main seal. This caused the clutch to slip even with this light load. This was just 3 weeks before our clubs big rally.

  The nose comes back off and the engine has been pulled. It only took us about 4 hours to have the engine out and upside down to work on.
  Once the crank was removed the cause of the seal failure was evident the rear main seal surface was pitted. Why this didn't leak when test run with out load is a mystery. The crank was sent out and just a trace cut resurfaced it and all of the mains this with new bearing inserts brought the crank back to spec.  


Three weeks later BEAUTY C60S and BEAST HUP at our summer rally.

 The next major problem for the C60 came after about 3000 miles and three years. A lose of power returning from an event was the first sign of trouble. The coprate was a burned exhaust valve in number six cylinder. It was interesting that when I pulled the head the cylinder walls had no visible or measurable ring ridge.


The burned valve is a result of the new unleaded gas from first sign of a leak to a very noticeable lose of power was only 150 miles all happened in one trip. All of the exhaust valves showed very noticeable recession. The valve clearance dropped to nearly "0".
Over the ten year Beauty attended a great many events as well as logging some 12,000 miles only one breakdown on the road stopped the truck. That happened on our clubs 2004 Fall Foliage Run. The symptoms- POP BANG WA WA. This all happedn while running along at 50 MPH, down hill, trying to catch the rest of the convoy. After coasting to a stop I had an idea that something in the distributor had let go. Popping the distributor cap off I gave the rotor a twist and it turned. The problem was a broken pin in the distrubutor gear
After 18 years on the road Beauty came home on the hook for the first time, going out for a Veteran Day event in November while only 3 miles from home, the recently installed freshly rebuilt 261 engine started making noises. First tick, tick, tick like a fan blade just touching the fan shroud. Put the gear box in neutral and coasted to the bottom of the short hill was on and pulled over. Fan OK restarted the engine the noise was louder and the vacuum gage needle was dancing from pin to pin. Not good had the truck towed home and the pictures below tell the story. A intake valve guide had broken and kept the valve from closing all the way. The top of the valve had just barely kissed the top of the piston. But with the valve stuck the valve push rod had been bent.

New Engine Information and Overhaul Progress on the Pattern 12