Originally Posted by zeehag
just prior to coming into marina we had runaway,. was stopped by cracking all 4 injectors, so we figgered it to be fuel delivery, aka injector pump. we got the lift pump and injector pump and the transmission heat exchanger rebuilt here and now we put it back together to find omg no go just literally ka lunk. so......onward and upward.....today we found the dirty injectors which does follow the history of this boat and this engine.
now we look for where the water is coming into cylinders so we can fix that and fix the cylinders and all the rest to be able to leave this precious pricy palace that costs arms and legs and such and continue on along my cheapo cruising lifestyle.
is perkins 4-108, probably built in 1982, or there abouts as the forging drop number is august of 1982.
FWIW - The reason that cracking the injectors stopped the runaway (I can't believe that someone did this on a running engine
) is that compression was lost. Whatever the source of fuel that the engine was running on, it could no longer ignite, due to the lower compression.
I don't know the Perky in particular, but the preferred way to stop a runaway is to block the air supply.
For the symptom that you describe, I would suggest that you put a socket on that big nut on the crankshaft and try to turn the engine over slowly. If you can do this, then the kerlunk is the starter/battery. However, if you can turn the engine, I would then try to VERIFY that you have the compression within each cylinder within spec.
It is likely that a connecting rod, or a bearing, went bye-bye. This is because the loss in compression when the injectors were removed, allowed the pistons to place unusual strain on the connecting rods and bearings (that the compression was no longer helping to slow these rapidly moving parts down). This is why those of us with compression release levers should NEVER use them to stop a run away engine. It is better to cram a cushion in the air cleaner.
I suspect that you may have a connecting rod that has detached itself from a piston, and is stuck against a cylinder wall. Turning the engine over slowly, and testing compression will help you diagnose if this is the case.