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Cummins Engine Question

H

Howard H.

Well-known Member

My Dad and brother overhauled an 855 Big Cam Cummins engine recently. It is a natural gas conversion.

It has a Starfire electronic ignition mounted on the harmonic balancer end of the crank and runs on natural gas.

After getting it mounted on the stand and everything plumbed in, it started right up and sounds good at low speed.

When trying to wind it up, though, it will only get to about half speed and start sputtering/backfiring/not running right...

Any ideas on what to check?? It seems to have gas pressure enough to run it... The main regulator was running this same engine before, anyway...



Howard
 
One thing to check first would be the timing then valve clearence.

There is such a thing called a polar diagram which is degree wheel showing the position of the crankshaft in relation to when the intake and exhaust valves open and close. That would be the best way to check valve timing. Let us know what you find out.
 
Howard,
Howdy! Sounds like the ignition is where the problem is,
either the Mag has crapped out or half working
or the ignition box has half way quit working.
Saw many a Mag do just that on HD 800 Molines over at LJ and Margaret's when I was there.
If you are sure the motor is "timed right" and the "valves are adjusted correctly" and the gas pressure is correct. it has to be the ignition! OBTW it isn't the Carb for you already said the engine started and got it to half throttle before it fell on it face. Hope this helps.
Later,
John A.
 
Did you have the rocker boxes opff? If you did don't forget that changing the thickness of that gasket pac changes valve timing.
 
Is it leaning out due to low LP flow?
Recently the conversion of choice for an LP industrial engine is NOT remove the injectors and NOT add spark plugs. That's old school and outdated.
The engine starts and runs on minimal diesel delivery. Varying amounts of LP gas is added to the intake manifold through a LP carb to follow HP demand.
Called pilot ignition. The amount of diesel is only ounces per hour.
Very simple, cheap, reliable and easy. Also allows use of diesel for backup fuel in emergencies or should fuel prices swing.
 
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