Challenge: Engine Diagnosis

[Celestialsailor]

Originally Posted by Kapena

I'm with the guys suggesting a connecting rod...but if you want a scenario of what if's then....

It can't be the flywheel, a bolt too long, or dampening plate. It would cause friction the entire rotation. Same for starter and transmission. Valve train would be 360 degrees, so that's left out.

Best bet is liquid in one of the cyclinders...you can't compress a liquid. So somebody took the hydraulic oil out of the steering and put it into one of the cylinders. That's what you will find...if it isn't a connecting rod.

...Thank you for the try...maybe you're right but I doubt a broken con rod would stop at 140 degrees in the same spot time after time.
...I relieved the valves to insure no hydraulic and again it would rotate past the marks I put on the flywheel.
There is also the possibility of something in the timing gears and also the input shaft of the transmission.

[Celestialsailor]

I'm lovin the bolt theory. I'm selling tickets at the hanging!

[nigelmercier]

If the engine has been sabotaged by someone who is interested in buying the boat, then they would not do anything that could actually damage the engine. I think this rules out any foreign bodies in the cylinders.

[Cheechako]

Originally Posted by Kapena

I'm with the guys suggesting a connecting rod...but if you want a scenario of what if's then....

It can't be the flywheel, a bolt too long, or dampening plate. It would cause friction the entire rotation. Same for starter and transmission. Valve train would be 360 degrees, so that's left out.

Best bet is liquid in one of the cyclinders...you can't compress a liquid. So somebody took the hydraulic oil out of the steering and put it into one of the cylinders. That's what you will find...if it isn't a connecting rod.

I like the logic, but... liquid wouldnt cause a "clunk" or "bang"....

[DeepFrz]

If the engine has been sabotaged by someone who is interested in buying the boat

I like that line. I will have to remember it for the next time I have a boat for sale...

[SkiprJohn]

Something obstructing the ring gear on the flywheel? Starter gear not retracting and jamming at 140 degrees?
We will be guessing all the way 'til Saturday and maybe longer.
No, Martin, I'm not going to throw a bolt into my engine to see what happens!
kind regards,

[sdowney717]

all I can think is the rod was thrown off the crank and likely when the engine was running. An immediate stoppage made a big mess of the inside parts. even if it the trans, you got to wonder if the inertial spinning movement coming to an immediate halt damaged the engine. I snapped a crankshaft in a diesel car engine. In that case the rear of the engine would spin with the starter while the front did not move. (GM Diesel off to the junk yard)

[Celestialsailor]

The plot thickens!

[Jesse]

Years ago I bought a new Pontiac for my favorite son's mother. On the second day after taking delivery she arrived home and said it was making strange noises. I went out to start it to listen and it went half a turn then clunk, and the same symtoms you are experiencing began. A racing buddy was running the dealers repair shop and he oversaw the teardown and repair. The piston ring lands were aparently too deep on one piston and it broke at the top compression ring and the strange noise was the lower portion of the broken piston rapidly and repeatedly colliding with the top, keeping it suspended till she shut it off. Then the top tipped sideways and fell into the lower half taking up most of the stroke and preventing it from a full rotation. There was surprisingly little damage but they still replaced all the pistons and valves.

[Coachbolt61]

I was replacing the starter motor (only 3 bolts) and dropped a washer between the flywheel and the casing. Buggar. The casing has webs for strength. It could have been a bolt getting stuck on the casing web. To fix you would have to remove flywheel to get to the bolt. As I had to.
Coachbolt

[Aerion]

A broken piston rod would allow 180 degree movement. I simple check with a plastic or wooden dowel in the injector holes would give you a lot of info. If they can be reached that is.

[steamgoat]

How about removing all the injectors, get a squeeze bottle of diesel and fill each hole. Then do the rock back and forth routine. If all rods and pistons are OK, all injector holes should ''suck or spit'' if a rod is broken one 'hole' will be silent ?????

[senormechanico]

Lots of theories here, most of them are good.
I have a new one, not necessarily good, but here goes:
If the boat hasn't been run for a long time and for whatever reason got salt water into one or more cylinders, rust caused a ridge in a cylinder and the piston rings hit it and won't go any higher.

I am watching with interest for the real answer.

[SabreKai]

Senormechanico has a viable idea. I had a BMW single cylinder diesel where that was the case. Sat in a fellows garden under a taro for a couple of years and water got into it somehow. When I pulled it apart there was a ring of rust about half way up the cylinder.

[captain465]

Don't think that a ring of rust would produce a "clunk" at 140 degrees in both directions.