Yanmar 4JH4-TE Catastrophic failure

[Scubaseas]

IMHO of pushing a wrench for 50+ years, it looks like a hydrolock issue. Flapper valve or check valve on the exhaust would be a good investment. A 3" exhaust can let a ton of water in on a following sea. Seen many a power boat hydrolock backing down for "fish on". Design issue? Maybe but not by Yanmar.

[jhulmer]

Originally Posted by Wotname

I think ReefM and Jimbunyard maybe on the money here.

Possible scenario - engine running at low rpm (1400), not much exhaust gas flow, cooling water pooling in the exhaust system and staying there until the exhaust back pressure builds up enough to push it out. Next lot of cooling water pools up but this time (at exactly the wrong moment), the stern picks up, boat starts surfing, gravity moves the pooled cooling water back towards the engine end of the exhaust. The wave possibly enters the far end of the exhaust and pushes the pooled cooling water far enough forward to hydrolock the aft most cylinder - game over!

Not saying this what happened but it seems feasible to me - a set of events that match the known facts. Of course there may be a another set of events that also explain the known outcome.

A close look at the conrod would be helpful. With a hydrolock I would expect the rod to bend before it broke. A latent defect in the rod should (IMO) show a developing crack face without any bend.

Hunterdog, was the broken rod nearest the flywheel? If so, in the Yanmar terminology, it is the #1 rod as the #4 rod is nearest the forward end of the motor (assuming no V drive).

I'm with Wotname here. I have heard of this happening. The engine that came out of my boat (4JH2) had a damaged #4 cylinder from water entering the exhaust out of the wet muffler during a grounding. In my research on how to prevent this with my new engine install, I read that this could happen if a big following wave hit the exhaust just right. Suggestions were to install a flapper on the throughhull or a backflow preventer. I have an engine below the waterline. I installed a riser on the engine exhaust and a large wet muffler that can handle excess water. The cooling water has to be injected into the wet exhaust on the down side of the riser to prevent cooling water from flowing back to the engine. I also routed the exhaust hose from the muffler as high above the waterline as I could get it before the Throughhull.

Jim

[mvweebles]

From the Yanmar manual for 4JH series.

Never mix different types of engine oil. This may adversely affect the lubricating properties of the engine oil. Never overfill. Overfilling may result in white exhaust smoke, engine overspeed or internal damage

No explanation how this would cause overspeed.

Given the number of exhaust systems that are now discharged underwater, I really don't think its feasible to hydrolock via a running exhaust under anything resembling normal operating conditions.

[Hunterdog]

Thanks peter.
Well, now the mechanic is saying there seems to be evidence of salt water, and thus some corrosion on top of the valves.

But about the speed thing: you’re right about the log. But after hours 10,000 miles over this past 18 months, and lots of motor-sailing, every conceivable combination of speed and attitude has been experienced on this boat.
Why does Beneteau have a sticker saying ‘keep transmission in neutral when sailing over 8 knots’. ???
BTW, it is pretty rare, and a ton of fun to keep over 8 knots for any prolonged period of time. I try all the time. (Motor off...)
So we are now at corrosion....do I suspect a bad exhaust design??

[Hunterdog]

Here’s some photos:

[Caravela1986]

My Opinion

Slug of sea water from exhaust hose caused the diesel engine failure.

Check spatial routing of engine exhaust hose. If horizontal and down, but no up
routing.............then a possible failure.

Normal cruising, with bow up, stern down, no problem cruising.

But, with rolling seas, long interval between wave heights, your yacht
pitches, bow down, stern up, with slug of sea water dormant in the exhaust hose because of slow speed( low power) lurches forward to the exhaust end of your engine causing the failure.

Solution ; There must be a tall rise upwards for your exhaust hose aft just before it exits the stern. This will prevent back flow of sea water to your engine,

Check your exhaust hose routing on your boat. Then it is fault of the yacht builder, not the engine builder.

[jhulmer]

Originally Posted by Hunterdog

Thanks peter.
Well, now the mechanic is saying there seems to be evidence of salt water, and thus some corrosion on top of the valves.

But about the speed thing: you’re right about the log. But after hours 10,000 miles over this past 18 months, and lots of motor-sailing, every conceivable combination of speed and attitude has been experienced on this boat.
Why does Beneteau have a sticker saying ‘keep transmission in neutral when sailing over 8 knots’. ???
BTW, it is pretty rare, and a ton of fun to keep over 8 knots for any prolonged period of time. I try all the time. (Motor off...)
So we are now at corrosion....do I suspect a bad exhaust design??

Yanmar cautions against leaving the trans in gear to prevent premature ware of the trans bearings.
the cone clutch in the trans will slip long before the prop could affect the powerful running engine. There is no way that the wave caused the prop to over speed the engine unless the prop came out of the water on top of the wave.

[Scubaseas]

From the Yanmar manual for 4JH series.

Never mix different types of engine oil. This may adversely affect the lubricating properties of the engine oil. Never overfill. Overfilling may result in white exhaust smoke, engine overspeed or internal damage

No explanation how this would cause overspeed.

Excess oil will vent into the intake, causing a runaway engine. Diesels are regulated by how much fuel is injected. More fuel, faster it goes. Supply an extra fuel and it runs out of control. Leaking oil from the turbo on the inlet fan will do it too.

[SaltyMetals]

A very close look at the fracture surface (possibly with a microscope) will show whether this was an immediate break or whether this was a partial fracture already that had been growing over the previous months. Not difficult. Standard stuff for a metallurgist.
andrew

[a64pilot]

Originally Posted by seabreez

I have seen engine failure of this type because the oil rushes forward and raised or goes up due to the curvature of the oil pan and hit the connecting rod and it was too much for the rod to displace all the oil in it's path. Very common in racing engines... that is the reason some engines have splash pans under the crankshaft bolted to the main caps to redistribute the oil evenly and prevent the oil from hitting the rods in motion. Some oil pans also have a baffle crossways with a door, to permit oil to go rearward and closes with gravity when the oil rushes forward. … my two cents worth... Roger

Oil will cause no issues of even very high speed motors if the crankshaft hits liquid oil.
Those splash pans your speaking of are called windage trays, they exist to keep the oil away from the crankshaft in high performance engines because the oil does have some drag and that robs power, not a lot but some.

If the crankshaft is running in liquid oil, like someone puts way too much oil In an engine which frequently happens about all that can happen is that the oil will get beaten into a foam, just like whipping cream, this foam will take up more space of course and the level will rise enough so that it will come out of the crankcase vent, if a Diesel it can then run away or at least blow a lot of smoke especially if it’s not a Diesel.
But it won’t break connecting rods.
https://www.eng-tips.com/viewthread.cfm?qid=17016

[mvweebles]

Originally Posted by Hunterdog

Here’s some photos:

Picture #1 and #2 show a broken end cap bolt. Does your mechanic believe the bent con-rod caused the bolt to break, or did the bolt break caused the con-rod failure? Or no way to tell?

I'm not the best mechanic, but it seems very difficult to get exhaust water to ingress into a running engine. To hydrolock in this manner, seawater would have to go upstream, against exhaust gases, past the lift muffler, into the manifold, past an exhaust valve, and into the cylinder - only one cylinder. This engine had been running for a while. I've not seen a hydrolock on a diesel, but have on motorcycles where a bike has fallen over and gas leaks into one of the cylinders. Enough throw for three of the cylinders to fire and force the hydrolocked piston to bend. A possible cause that we haven't discussed yet is some sort of leak on the injection pump or lift pump that dumps diesel into the crankcase. Accordingly, would cause a runaway condition which would result in something giving way - con-rod or bearings are what go.

As mentioned, as a single-engine trawler guy, very interested to get as much info as possible. Sorry for your issues Hunter, but a good learning experience for me so appreciative that you're sharing.


Peter

[Hunterdog]

The oil was correct. And was serviced regularly...

[a64pilot]

Hydrolocks or partial hydrolocks are very damaging, and very often will over stress a component often a connecting rod, but not break it, but will start a crack, later it breaks.
If there is evidence of salt water intrusion, I’d bet that scenario is very much more likely than a hydrolock while running at 1400 RPM.
Anything can happen, but that’s not very likely.

Very rarely does something just break, what almost always happens is it breaks due to cumulative fatigue.

For a price that connecting rod can be analyzed, it’s often done on aircraft as part of an accident investigation etc. did the part beak in the crash, or break and cause the crash?

But other than knowing how it broke as in fatigue and crack growth or sudden overload, I’m not sure you could do anything with that info.

[jacktheflyer]

Originally Posted by Scubaseas

IMHO of pushing a wrench for 50+ years, it looks like a hydrolock issue. Flapper valve or check valve on the exhaust would be a good investment. A 3" exhaust can let a ton of water in on a following sea. Seen many a power boat hydrolock backing down for "fish on". Design issue? Maybe but not by Yanmar.

Agree. Seems pretty certain. Those pictures don't show an over speed failure. I'd be looking for how it got hydrolocked.

[mvweebles]

Originally Posted by jacktheflyer

Agree. Seems pretty certain. Those pictures don't show an over speed failure. I'd be looking for how it got hydrolocked.

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.