VX200 OX66 - Knocking sound

[99yam40]

Never heard of a rope in prop taking out a cylinder.

Sounds strange

Post what they find when the open it up and what they think caused it

[TownsendsFJR1300]

Got the results today...6th cylinder is busted.

As in a cracked cylinder???

[kmswiber]

I picked up the boat today...he said the ring was busted. Would cost around $2000-$2500 to replace.

He didn't see anything in there that could've caused it. He thinks it is simply a mechanical failure.

There's just too much coincidence with the rope and shallow water. When I *****ed passed the area I took off near I saw I kicked up a lot of mud.

[boscoe99]

Some times two completely random events happen at the same time.

On another forum a guy reports that his two motors failed at the same time. He is convinced that something external caused both to go at the same time. Maybe so. But maybe not.

Some stuff cannot be known. They spend millions and millions of dollars trying to find out why airplanes crash. In most cases they can only guess. They call it "probable" cause because it sounds better than "our best guess". Which is all that it is.

[scofflaw]

never heard of a broken ring knocking

[boscoe99]

never heard of a broken ring knocking

Now you have.

Without the rings to keep the piston in check it can slap the sides of the cylinder walls and make a knocking sound.

[scofflaw]

Now you have.

Without the rings to keep the piston in check it can slap the sides of the cylinder walls and make a knocking sound.

Tell me how the broken rings come out of the groove. Piston would have to be broken in half at that point for that to happen. Ring width would be far greater than piston to wall clearance.

[boscoe99]

Tell me how the broken rings come out of the groove. Piston would have to be broken in half at that point for that to happen. Ring width would be far greater than piston to wall clearance.

I am presuming that the piston is also broken. Or parts of it.

Lots of dynamics going on in a combustion chamber. Something breaks and parts flapping around or flying around causes other stuff to break.

Now is this what happened in the OP's motor? I have not a clue.

https://www.google.com/search?q=imag...HVfMDY4QsAQIGw

[kmswiber]

I am presuming that the piston is also broken. Or parts of it.

Lots of dynamics going on in a combustion chamber. Something breaks and parts flapping around or flying around causes other stuff to break.

Now is this what happened in the OP's motor? I have not a clue.

https://www.google.com/search?q=imag...HVfMDY4QsAQIGw

Boscoe99, I don't know. He just said the ring was broken in the 6th cylinder. I really wish he took pictures for me. I have an insurance guy coming Saturday. I think I'm going to get a new motor...I'd hate to buy a used one and go through the same situation. Wish I could sell the boat, but it is hard without a working motor.

[TownsendsFJR1300]

I wonder if he pulled the head....

[kmswiber]

I wonder if he pulled the head....

He told me he did...I know a little about fuel lines/pumps, same with the oil side. But all of this is over my head. Everything he told me I posted on here.

Thanks again for all the comments/suggestions.

[TownsendsFJR1300]

Something just doesn't sound right...

Will your insurance guy need a detailed estimate of the damage?

He (the mechanic) would have to put down more than "a broken ring", ie bore cylinder, new piston(s) labor to R&R power-head, tear down, gaskets, machine work, etc.

#6 cylinder is down low at the bottom, your noise is way up (the noise can echo). A ring break from a sudden engine stop, never heard of it. Broken flywheel key, broken crank-does happen but rare (and in your instance shouldn't have)

You may consider a rebuilt power head. If not, part out the LU, carbs, etc and get some of your $ back...

[scofflaw]

Head off won't reveal much. Exhaust manifold off will give a nice piston profile

[TownsendsFJR1300]

Head off won't reveal much. Exhaust manifold off will give a nice piston profile

Agreed, but depending on what he saw in the top end with the head off may have been enough.

[zenoahphobic]

Sorry, coming in late again.

1. Boscoe, I don't believe a broken ring (even completely removed) allows the piston to rock and make slapping noise (nonsense); even less so on one cylinder in a six setup.

2. the knocking can be the ring contacting with the exhaust port, many a ring once broken can exit this way. If that is the noise then there will be some mess!

3. Townsend a ring can break with a sudden stop in a two stroke engine; rare but can occur with close tolerances such as engine beginning to overheat leading to ring expansion (lenghthening); the sudden halt in momentum throwing the piston and ring further into the exhaust port opening, and a snag or sudden compression of the ring back into the bore. Mind you this would be at high revolutions causing destructive shock to the brittle ring.

Please advise what has probably now been inspected.