Strange thing happened today

[Gulf Islander]

This was a first for me. Tried to start my diesel and it would make a quarter turn and then stop. Big Clunk. Tried it again and same thing. I then grabbed a pipe wrench and turned the crank quarter turn then stop. I scratched my head and then decided to reverse crank and it was free. It was all of a sudden it was free. I started the engine and it has been running for the last 3hrs just fine. What could have cause this.

[senormechanico]

Watching this thread with interest !

[belizesailor]

Hmmm, whatever it is dont sound good.

A temporary obstruction of some sort, that reversing it cleared? But what was it and where did it go?

[Suijin]

I'm thinking it is starter related but that's because I can't think of anything else lol.

[atoll]

it sounds like a possible hydro lock,ie water in the exhaust entering a cylinder
but could also be bad contacts on the solenoid.

[a64pilot]

Originally Posted by atoll

it sounds like a possible hydro lock,ie water in the exhaust entering a cylinder
but could also be bad contacts on the solenoid.

Not with a big clunk and unable to turn with a wrench.
Most likely hydrolock, best get to the bottom of that fast. I'd start with exhaust elbow

[Jim Cate]

Originally Posted by a64pilot

Not with a big clunk and unable to turn with a wrench.
Most likely hydrolock, best get to the bottom of that fast. I'd start with exhaust elbow

Complete agreement! Had similar symptoms years ago when we first set out cruising in our previous boat. Had worked fine since purchase, then we loaded her up with all our cruising gear, the WL came up a couple of inches (maybe three!) and it started back siphoning into the exhaust and eventually into a cylinder. The idiot who had installed the engine had no bleed or vacuum breaker in the line injecting water into the exhaust, and the idiot owner (me) didn't know better either... then!

Good luck with finding the source, but it sounds like so far you have dodged a very expensive bullet.

Jim

[shakey doug]

Something dropped into gear train by reversing it fell away -----Possible.

[taxwizz]

May I ask what engine it is?

And...did you do anything with the Pressure Release valve?

[Elie]

Hydrolock would not clear by turning the engine backward, in my opinion. I'm thinking of a flywheel or starter problem. But most probably a starter with bad tooth.

[boeing1]

I think I would look at the starter for condition and security

[Symphony]

Not likely Hydro lock because that would not go away By cranking it backwards, would it?

Not likely something in the valves or timing because one clunck would have damaged it permanently?

The only thing heavy enough to take a hit like that and not break must be a starter gear on the flywheel?

[Matsubob]

There really is too little to go on, but since the engine wasn't at the point of starting yet, it would sound like it was starter related. Like the bendix wasn't fully deployed by the solenoid and it jammed. If cobustion had started, though, the engine would have destroyed the starter gear.
Waterloc is questionable, because even if backing the engine were to have cleared any water in a cylinder, it sure wouldn't have run smoothly at first, if at all.
Then.... if it is something internal, like a chunk of metal picked up by the timing gears and getting dropped upon reversing, possible, but very serious!
I would sure not ignore it. Check the starter pinion, solenoid action and actuator, as well as the bendix. Then, change the oil and look for filings or signs of any kind of internal trauma.

[Dave_S]

If there was water in it it would have cleared if you turned it back past top dead centre again as on the other TDC cycle the valves would be open and the water ejected.

If you turned it back that far?

[Maka]

I agree. Check the oil 1st for any clues.