Yanmar 4JH4-TE Catastrophic failure

[Mike Banks]

Did the big end bearing cap bolts come adrift? I have heard of that--it even happened to me on a petrol motor where they had used some sort of locking compound on the bearing cap nuts instead of using bolts with castellated nuts and cotter pins.

Apparently some oils have a solvent in them which dissolves that stuff they use to lock nuts. If that is the case--you need to make sure your engine uses only the recommended oil, and that the crankshaft has only castellated nuts and cotter pins for locking once torqued up to the proper setting.

If the con rod just broke--that sounds SO unlikely under normal usage--and it was no over-revving that caused it. It needs a proper metallurgical examination to determine if it was a faulty forging--and I think Yanmar con rods should be drop forged and machined--not just cast and finished from re-cycled scrap.

The only cause of such a failure that makes any sense to me is a lungful of water, fresh or salt--that will usually do it. It would be my diagnosis anyway.

[mvweebles]

Originally Posted by Mike Banks

Did the big end bearing cap bolts come adrift? I have heard of that--it even happened to me on a petrol motor where they had used some sort of locking compound on the bearing cap nuts instead of using bolts with castellated nuts and cotter pins.

Apparently some oils have a solvent in them which dissolves that stuff they use to lock nuts. If that is the case--you need to make sure your engine uses only the recommended oil, and that the crankshaft has only castellated nuts and cotter pins for locking once torqued up to the proper setting.

If the con rod just broke--that sounds SO unlikely under normal usage--and it was no over-revving that caused it. It needs a proper metallurgical examination to determine if it was a faulty forging--and I think Yanmar con rods should be drop forged and machined--not just cast and finished from re-cycled scrap.

The only cause of such a failure that makes any sense to me is a lungful of water, fresh or salt--that will usually do it. It would be my diagnosis anyway.

My opinion, bolt on end cap being improperly torqued at time of manufacture is a 100 times more likely the cause than hydrolock from exhaust. Odd that that the bolt broke. When the con rod breaks, the force is straight down onto crank. No reason to break the bolt. But who knows, when something gives way in a cylinder of a running motor, all hell breaks loose. No telling where the forces are.

I do think the broken bolt may be a clue.

[mvweebles]

I'm sorry, you'd have to invest a large amount of water all at once - through the exhaust. This was a hot and running engine. Small amounts of water would be burned off as steam. So somehow, you'd have to get a LOT of water upstream, past the exhaust, past the exhaust valve, into the cylinder when the cylinder was in the downward stroke, before the exhaust closed. On a boat that is floating on her lines (more or less given the sea way). That's a moon shot by a caveman.

[osprey877]

The Photos in post 35 show the piston in pieces. So if that cylinder hydro locked, wouldn’t there be a big slug of seawater in the oil sump, which would have been apparent to the mechanic??

[rlamoureux]

Much agree that the Beneteau - Yanmar- ZF marriage à trois is really bad. Ended up replacing both VCU and TCU harnesses on the Dock&go. Fingers crossed on working reliably now.

Anyhow, how do you take out the Yanmar engine on a Sense? Or must you take it apart insitu? Thanks

[Jim Cate]

I'm now a bit confused: did the rod break or just the big end bolt, causing the bending of the rod (to me, rod appears to be bent rather than broken ). Or did the piston fail first, jamming the rod, causing it to wedge into the cylinder and then the cap bolt broke on the downstroke?

Good question about water in the oil, too.

A good puzzle.

Jim

[jimbunyard]

Both valves are still intact and in the head, right?

If so, then the following picture, regardless of some people's ability to imagine it or not, pretty much proves, against apparently almost infinite improbablility, that, given the proper conditions, the water the vessel is floating in can enter into an engine's exhaust whilst the engine is running.

Of course, a little reflection on the operation of a water lift muffler might shed some light on the subject.

The fact that the forward cylinder was the one killed further verifys it; when the boat surfed down the wave face the water that had collected or been forced into the manifold ran down and enough got into the forward cylinder to bend the rod, which caused the piston to sieze in the bore, almost simultaneously tearing the piston apart and breaking the rod cap off.

Conversely, the water got in the cylinder, bent the rod (and that's a damn serious bend), then the rod wedged against the cylinder wall, breaking the cap off. The rotation of the crank grabbed the big end, pulled it down far enough so that piston was pulled into contact with the spinning crank, which then chewed it into the pieces shown in the other picture.

Obviously, I'm just making things up, but they're informed stories. Find the right person to analyze the marks on the affected parts and the sequence of events will become clear, and it shouldn't take metallurgical experts or microscopes to do so, though they might provide insight if things turn out to be different from what we've been told and can see indicate.

How does the picture 'prove' this? Notice the straight red line? The rod is supposed to be straight like the line. Rods don't bend after the cap or cap bolts break, at least not like that. The rod in the picture bent because the crank tried to compress something incompressible.

If a valve wasn't dropped, what else could have gotten in there?

Again, although the exhaust diameter recommended by Yanmar could certainly have contributed to the catastrophe, good luck making that stick.

Don't think you'll have much better luck with Beneteau, but they designed the exhaust...if you have or are putting a new engine in (couldn't tell from your original post), it surely seems that you should get a couple or three different opinions on the design of the current exhaust system.

Or it could have just been a fluke. What are the chances of it happening again?...

[Wotname]

Originally Posted by mvweebles

I'm sorry, you'd have to invest a large amount of water all at once - through the exhaust. This was a hot and running engine. Small amounts of water would be burned off as steam. So somehow, you'd have to get a LOT of water upstream, past the exhaust, past the exhaust valve, into the cylinder when the cylinder was in the downward stroke, before the exhaust closed. On a boat that is floating on her lines (more or less given the sea way). That's a moon shot by a caveman.

Re-read post #18 (Jimbunyard) and some others in this thread for a creditable explanation of how a possible hydrolock might occur.

This engine was only just above idle (OP reports 1400) and well under half of it's rated max rpm. The exhaust gas flow (and pressure) would have been very low. The exhaust gas temperature would have also been very low.

The volume of the exhaust system is likely to be oversized even for its max rated rpm thus very oversized for running at 1400. The amount of cooling water in the exhaust system at these conditions builds up until it gets expelled after some seconds (5 to10).

The OP reports a surf (or wave slide) from a following sea which as others have suggested can force exhaust water back towards the engine.

The rod is clearly bent (last photo in post #35) and the piston is smashed (also photo in #35). The only things that do that is a incompressible item in the combustion chamber - usually a liquid or a valve.

Clearly it hasn't dropped a valve so that leaves a liquid. It doesn't take that much, maybe a tablespoon or so will do it.

No report of a blown head gasket so that sort of only leaves exhaust water - only a small amount from an unfortunate combination of events.

IMO.

EDIT : Jimbunyard posted at the same time but explains it better than mine

[Wotname]

Originally Posted by osprey877

The Photos in post 35 show the piston in pieces. So if that cylinder hydro locked, wouldn’t there be a big slug of seawater in the oil sump, which would have been apparent to the mechanic??

Might only have been a small slug of seawater and was sitting in the bottom of the sump thus not noticed by a lesser mechanic. Engine didn't run for long enough to emulsify the oil/water.

Just speculation of course

[skipperpete]

I’ll take a guess and throw in the possibility of a dropped valve but only because I can’t see how a hydro lock could occur with an engine running at 1400rpm. It looks like the bearing cap was still held on by the other conrod bolt because it’s not stripped broken or bent. No sign of overheat seizure on piston skirt either. I’d love to see a picture of the head and piston crown. I think this is a possibly a 16 valve engine with those pesky crossheads that need adjusting at the same time as valve lash setting. Of all the Yanmar’s , this is the one I’m not too keen on..... mostly because of the injectors under the valve cover.
Just a guess, and I hope the real cause of the failure is eventually found.
Pete.

[a64pilot]

Originally Posted by mvweebles

How the heck do you you hydrolock a running engine? I'm a damn good shade tree mechanic (past delivery skipper who can bandaid anything), but I'm far from an expert. Given the path and impediments of seawater going against exhaust on an engine that has been running fine for several hours, I just don't see it.

The con rod broke. It's a huge stretch for me to say hydrolock.

It was hydrolocked or partially so previously, assuming there is evidence of salt water intrusion that is what I would be looking for.
I could see maybe an engine at idle getting water in, maybe, but not at 1400 RPM.
The over speed thing is a red herring, it’s just not possible or we would all see massive over speeds every time we drove our cars downhill, and we don’t, plus a prop just can’t drive an engine up much in RPM at all.

[Wotname]

Originally Posted by Jim Cate

I'm now a bit confused: did the rod break or just the big end bolt, causing the bending of the rod (to me, rod appears to be bent rather than broken ). Or did the piston fail first, jamming the rod, causing it to wedge into the cylinder and then the cap bolt broke on the downstroke?

Good question about water in the oil, too.

A good puzzle.

Jim

Hmm... my guess - piston on the compression stroke (i.e. going up) finds water in the combustion chamber. Rod bends and piston breaks.

Bent rod and broken piston pieces continues though a few more strokes (valves still working and broken piston so no more hydrolocking) until a piece of piston jams the rod in the cylinder and a cap bolt breaks on an upstroke.

But hey, there are other possibilities for sure

[a64pilot]

Originally Posted by Mike Banks

Did the big end bearing cap bolts come adrift? I have heard of that--it even happened to me on a petrol motor where they had used some sort of locking compound on the bearing cap nuts instead of using bolts with castellated nuts and cotter pins.

Apparently some oils have a solvent in them which dissolves that stuff they use to lock nuts. If that is the case--you need to make sure your engine uses only the recommended oil, and that the crankshaft has only castellated nuts and cotter pins for locking once torqued up to the proper setting.

If the con rod just broke--that sounds SO unlikely under normal usage--and it was no over-revving that caused it. It needs a proper metallurgical examination to determine if it was a faulty forging--and I think Yanmar con rods should be drop forged and machined--not just cast and finished from re-cycled scrap.

The only cause of such a failure that makes any sense to me is a lungful of water, fresh or salt--that will usually do it. It would be my diagnosis anyway.

I’ve never seen connecting rod bolts, or Crankshaft bearing caps held on with nuts and cotter pins, not even on an aircraft engine.
What kind of engine did you have?

[mvweebles]

Check the water injection exhaust elbow. If water did get in, would be there. Scooping it from the transom of a boat moving forward with engine running makes zero sense. Maybe if you were seriously pooped - maybe.

If the bolt on the end cap let loose due to human error during install, a pretzeled conrod would be highly possible though I concede it should make a helluva racket beforehand. I agree, looking at head would be helpful. Regardless of what happened, should have bent valves. Piston danced around with vigor for a while.

I look forward to updates.

[wingssail]

Boy, that thing got busted up good!

I tend to believe the hydrolock theory; the bent rod happened when the spinning crank pushed the piston up against something incompressible.

Probably water.

And that's a bit discouraging for all of us.

I have no flap on my exhaust outlet, and it is down at the tip of my transom.

Well, the stern of my boat does rise pretty easily, and the exhaust hose goes up 4 feet before going down to the outlet.

And in all of our sailing, and plenty of following seas, even some with the engine running, I never had that problem.

Lucky me I guess.