The detroit 2 cycle engines have a flap that when unlatched the springs force the flap to close the air intake. a system like this would stop a lister even with the rack all the way to the full speed position. a condition that could happen when a pin falls out.
Dennis
all I've ever seen those sutters used for is keeping crap out of the blowers when servicing the intercoolers and turbos.
unless your blower seals were in good nick closing the flaps would such them and their oil in too
detroits scare me, maye they wouldn't if i'd done the factory course, but that whole convoluted rack / injector thing is sooooooo easy to get wrong, or make wrong with a light hammer blow
listers have an almost exposed valve chest, so undo one handscrew, pop the cover off and whack the collets right and the valve will drop down and decompress the whole engine >;^)
on a more serious note, there is SOMETHING THAT NEEDS TO BE SAID here.
these old style external flywheel motors have abso-fucking-lutely massive inertia in the flywheels when spinning at 650 RPM.
you think a 2" dia crankshaft is tough?
I wouldn't try dumping all that inertia quickly, eg breaking a pushrod, it would be tantamount to sticking a fire hose in the intake, sure it'll stop the engine, but it better blow a neat hold through the piston crown because if the piston or rod tries to sieze that 2" crankshaft will snap like a glass rod.
shutting the rack is nice, and shutting the rack and decompressing (assuming your listeroids are set so you can do that at speed without crowning the valve?) is very nice
nothing that stops (eg 0 rpm) the motor in less than fifteen seconds will be nice
if the listeroid design follow the lister then the only way you'll get a diesel fuel runaway is if the rack is wide open
if you have a lube oil runaway (from oil bath air filter or passing rings) then shutting the fuel won't shut her down anyway, listers run on minute amounts of fuel.
if you have a lube runaway then you, by definition, cannot cut off the "fuel", so you can only cut off the oxygen, either by sealing the intake, or flooding it with co2, or by closing the intake and exhaust off together
if you're running a gen head then overspeed also = over Hz, which will probably trip out your loads, and let the engine spin even faster, the beauty of the start-o-matic was the combines Ac/DC head, even if ac tripped out overspeed, dc was still produced and dc solenoid was the standard shutdown method.
so you want.
1/ auto shut down the works
2/ auto shut down that does not interfere with or over ride run away shut down
3/ run away shut down that doesn't depend on anything except the engine, eg not ac only gen head
so
1/ auto shut down can work happily by controlling rack and / or decompressor
2/ run away shut down can work happily by closing intake
item #2 is faily easy to make up, and fairly cheap.
on the air intel, most people fit a 90 degree elbow up to an air filter, don't, fit a tee, make sure it is a reducing tee, like this
this is a slightly exaggerated example
the small diameter should fit the lister intake.
now all you need is a lathe and a surplus ball bearing.
make and insert a seat (for the ball bearing) in steel, set it at the lister intake end of the tee and spot weld into place.
on the top of the tee goes your air filter as usual
in the other end of the tee in direct line from the lister intake you put your ball and actuator, eg a suitable spring, end cap and release mechanism (you could make a piston type plug out of brass rod instead of using a bearing)
TRY THE BLOODY THING ON THE BENCH, both at room temp and at least 150 celcius to make sure it don't sieze, you'll also have to keep that thing clean from dirt etc so the ball can't get hung up, just a little though will do.
don't make it do it as a perfect seal, you NEED a moderate amount of leakage, say 1 cm square, to prevent damaging the engine by turning it into a vacuum pump on the induction stroke, she won't run fast on an intake 1cm square
if you try and turn it into a vacuum pump you cut off cooling air and may make her suck past the valves
if you try it on the exhaust side you risk popping the head or piston
make sure the tee is THICK walled, so it doesn't break and open up the intake again
personally I'd trigger it by intake manifold vacuum.
if you do NOT run an oil bath air cleaner, the only way to get "fuel" up there is past the rings, so an "overflow" in the crankcase would stop dilution, which would stop spattering excess up the bore, and a very lightly spring loaded alloy crank case door would stop excess crankcase pressure from blowing anything up there, but neither of these will help if something goes wrong and the rack jams open***
***I can distinctly recall and enamel coffee cup vibrating off an old tangye, and being batted by the spokes straight into the governor linkage, which luckily is bent shut, not open.... most embarrasing as it was my coffee
