Thanks for all this, extremely illuminating. I've seen several cars with hydraulic lock from water - driving through floods, at the beach. It once happened to my wife when her car was submerged. But it never occurred to me that it could happen from fuel. Anyway, see more below....
Hydraulic lock occurs when one cylinder or more fill with petrol. This condition can occur when mucking around with the FD on K jetronic resulting in a continuous stream of fuel squirting into the cylinders. I have encountered this problem myself...as have quite a few other folk ...who have delved into the wonders of K jet.
This most definitely DID occur, at least briefly, and the engine was cranked until it was clear that it wasn't going to fire.
But having now read your earlier threads on starter motor -to ring gear- to fuel distrib, something tells me this is a problem that is all related and has been some time in the making. Seemingly, the case for conventional "cylinder hydraulic lock "seems to weaken partic as you have removed the plugs. ie the lock up is not in the cylinders. You have removed all the plugs ?...yes?
Yes, removed plugs. But the borescope arrived. Same day delivery from Amazon! Sso I'll be having a look inside anyway shortly.
It is drawing a long bow, but it is possible to jam a motor from turning if there is too much oil/fluid in the sump.
Hence my suggestion to drain it. As u are aware the 6.9 is dry sumped. This is a bit misleading coz of course it has a sump but only to collect and scavenge. Oil supply management is drawn from the reservoir tank. It is theoretically plausible and possible for the sump/crankcase to overfill and lock the piston downstroke. There are a couple of ways this can happen...all of them bizarre. Impossible I hear the experts chortle!
Ordinarily in this motor, the scavenge pump would keep the sump at the right level even if it had filled with surplus petrol draining from the cylinders past the rings and into the sump...
But what if the scavenge side of the pump is not returning the oil to the reservoir? The reservoir would be empty and the sump would be full.
Interesting. What scenario(s) would cause this to happen apart from pump failure?
So you need to determine that the oil level in the reservoir is in the right range [yes I know..that level is determined when the engine is running but we can't run the engine ]HOWEVER...a static dip of the tank will tell you if it's emptyish. If heaps comes out of the sump then you have the answer.
We'll know the answers in a few hours! Keeping my fingers crossed that this IS the case, and nothing else is broken. Thanks again. This mystery deserves a youtube channel with millions of followers. Cheers,