fuel shutoff stays applied

[Brian R.]

I have a 6v92 with an air activated (from a skinner valve) fuel shutoff piston that pushes the fuel shutoff lever.  Problem is that it stays applied most of the time.  I have to crack a fitting in the air line to vent the air then the piston retracts and I can start the engine.  I'm assuming that the piston housing should have a vent hole so the air can escape after the initial blast triggers the piston.  Haven't pulled it off yet to look but is this the correct thought or is something else involved ?  Thoughts appreciated.

[luvrbus]

Take the air line off the shut down cylinder 1st and see if the skinner valve is working both ways  off you should air, starting and running you should have no air to cylinder,they do have a vent on the front plate with the 2 screws they also have a spring  inside to return the piston with no air,they vent at the skinner valve,the vent on the cylinder is for when the piston extends for shut down

[Coach_and_Crown_Guy]

There may also be a real reason some system is not releasing the Skinner valve to let the engine start. Maybe a relay that energizes the Skinner? Another thing on the manual transmissions is a neutral safety switch on the linkage that won't allow the engine to crank over if in gear. The automatics also have a neutral safety switch so it's in neutral. Be sure to check all the upstream systems and interlocks ahead of the Skinner valve and air actuating cylinder pushing on the stop lever. The final fail safe procedure should be to remove the airline from the actuator cylinder so the engine will run and then stop the engine by hand by pushing down the stop lever. I know this sounds like merely engine cranking interlocks but there may also be engine stop/run tie-ins to be considered.

Another thing to Really look at is to check out thoroughly the proper switch position settings on the mechanics panel in the engine bay. Are the switches themselves in the correct position for Front/Rear operation and is the Safety switch engaged which kills the cranking and probably the Skinner valve too. The switches MAY be faulty or even the panel has been tinkered with through the years by "Mechanics" and may no longer operate as designed. Question EVERYTHING and don't make assumptions that because it looks OK that it's really working as it should. The Skinner and air actuator are the very LAST operation in the chain of logic events that create the condition for engine Stop/Run. If something isn't right up-line they are not the true cause of the failure. You can override and remove the air line which I've done in the past to get the bus home, but the real fault needs to be rooted out and repaired. One reason I like the pure mechanical engines so much.

[Brian R.]

Thanks for the tips guys. I'll be running this down soon, (finishing up a new propane compartment at present).  Skinner valve that I installed is hard to reach, as usual, but then what isn't. At least I know it isn't a neutral safety switch issue as I have none on this 1960 bus. Will checkout my rear panel start/stop for proper function. I was thinking maybe the stop switch was staying energized but the after I crack the airline and hook it back up it stays off. Will check with multimeter when it is stuck on.   Cheers Brian R