Bent Con Rod

[Chief Engineer]

Never Monday will probably back me up on this.

When I worked aboard tugs, the Fairbanks-Morse Opposed Piston Engines overwhelmed me at first.
The Port Engineer saw that I was taken aback by them and said 3 things
"Look for the simple things first, keep the fuel clean, and never EVER let the Captain MUCK with you engine room."

The bottom line is...you have got to find out what the problem is and gear your
work to correcting it and the damage it caused.

There are way too many bad wrenches" that just throw parts at engines, praying that something fixes it

[toddt]

Thanks for all the input everyone. The engine is in a 1984 Hunter 34. The way I hydro-locked the engine was forgetting to close the raw water sea-cock (how I forgot I have NO idea) while trying to get the engine started after a secondary fuel filter change. I'm going to try to pull the head to make some measurements this week after purchasing a few tools. I will post any and all findings as I go. The real tragedy is the engine is less than 3 years and 400 hours old.


Thanks Again

[never monday]

Originally Posted by Chief Engineer

Never Monday will probably back me up on this.

When I worked aboard tugs, the Fairbanks-Morse Opposed Piston Engines overwhelmed me at first.
The Port Engineer saw that I was taken aback by them and said 3 things
"Look for the simple things first, keep the fuel clean, and never EVER let the Captain MUCK with you engine room."

The bottom line is...you have got to find out what the problem is and gear your
work to correcting it and the damage it caused.

There are way too many bad wrenches" that just throw parts at engines, praying that something fixes it

Whats the old Army principal...keep it simple stupid?

In this case If I was considering but not sure of a bent rod I wouldn't yank it out and tear it down as the first step.
I'd pull the injectors and with a coat hanger get a decent measurement of the 3 cyl strokes the engine was making. If one cylinder has a bent rod it will be noticeable on a simple swept volume test.
Because of some things Todd told me on the phone I'm leaning him to pulling the head and visualizing the pistons crowning over the block. From there it'll be a simple mater to drop the pan and pull the pistons and rods out.
I have had knocks from atomized water before. They usually clear in a few min of run time. This engine has been run for over an hour since the knock developed. Something is going on in that cylinder.

Never, Never let a Capt in your engine room (and lie to him when he asks how it going)

[Xtofinooic]

Hi Toddt, I sail on a friends Hunter. We had noticed that the eng (Yanmar 3gm) Has not been running properly. It appeared to be missing on one cylinder. At times it seemed OK, then it would show white smoke at times at others blue smoke. I fig'd he had a bad injector (white smoke) and perhaps a bad valve seal (blue smoke) He took it into a marine mechanic. Turned out he had two bent rods one considerably more than the other. The eng was pulled While doing the job We had him hone the cylinders reseat valves, 3 new conrods and conrod bearings. Crank checked out OK. Next question was, how did water get into the cylinder. First thing (I still can't believe it but have the part to look at) The connecter from exhaust manifold to the exhaust pipe which has a water prevention loop (inverted U) had an amazing feature. In that the pipe putting raw water back into the exhaust is on the wrong side of the preventor. IE the water went in on the manifold side of the preventer instead on the exhaust pipe side. Then there was an anti syphoning loop with a valve at the top On the raw water line leading to the exhaust pipe. So now when you stop the eng. The raw water in the raw water line bleeds into the exhaust pipe (Enough water to fill a 1/2" hose about 18in in length) and because the induction pt is on the wrong side of the preventor and there is no outflowing exhaust (the eng has been stopped) the water can run back into the exhaust manifold and down into a cylinder. Stupidest system i ever saw. This is on a Hunter Production model that had not been messed with. To prevent this from reoccuring A much longer exhaust Prevention loop was installed About 10 in high as opposed to the original one about 2 inches high. The Raw water is introduced into the exhaust line well onto the exhaust side of the elbow. The nipple is pointed in a downward direction not just at 90 deg to the pipe. This longer pipe requires Heat tape and lagging on the dry side of the line. We also chnged out the muffler to a muffler with a one way valve re water. Nothing comes back up the pipe esspecially when involved in some rigorous sailing. The eng is running like a sweetheart. It was an expensive fix. The engine had about 1000 hours on it.
The mech. had recently done another Yanmar with the same problem It was another Hunter from our Club. The main cause here in my minds eye was the introduction of raw water on the wrong side of the exhaust elbow. So basic that you can't believe it when you see it. The elbow can only go on one way as the manifold side is threaded and the exhaust end is designed to take a rubber exhaust hose. as this part i believe is one supplied by Hunter I wonde how many more Hunter owners are out there with bent conrods caused by a mistake in design of the exhaust elbow?? Should launch a class action on this one.