Internal Mechanical Failure vs. External Impact? Severe Damage on Caterpillar 660 HP at Turbo Spool (No Felt Impact)

[betulio602]

Hello everyone,


I am looking for insight and technical feedback from the community regarding a recent failure on a 48-foot yacht powered by twin Caterpillar 660 HP diesel engines.


Background:


A month ago, after weighing anchor and stowing fenders, I was accelerating slowly out of a beach area. Right at the moment the turbos began to spool up and build boost, an extreme, violent vibration occurred in the port engine. I immediately pulled the throttle back to idle, and the engine shut down completely.


Key point: At the helm and throughout the vessel, NO impact, thud, or collision with any submerged or floating object was felt.


List of Confirmed Damages:


Cracked cylinder head / valve cover.


Two broken / dropped valves.


Damaged / destroyed turbocharger.


Shredded Vulcan flexible coupling.


Broken engine mount / support bracket.


Unbalanced / bent propeller shaft.


Unbalanced / distorted propeller.


Damaged cutless bearings (strut bushings).


The Controversy:


Local mechanics insist that the root cause was hitting an underwater object. I strongly disagree. An external impact severe enough to bend a shaft and break an engine mount on a 48ft boat would have caused an unmistakable sound and structural shock throughout the entire hull.


Our Hypothesis:


We suspect a catastrophic internal failure occurred—such as a hydrolock (coolant/water/fuel ingestion via aftercooler or turbo) or a dropped valve due to fatigue—right at peak torque demand during turbo boost. The instantaneous internal lockup of the engine at high RPM, contrasted with the propeller's rotational inertia in the water, created a massive reverse rotational torque. This load sheared the Vulcan coupling, snapped the engine mount, and warped the shaft from the inside out.


Questions for the Community:


1. Have you ever seen an internal engine lockup (hydrolock or valve drop) cause this level of rotational and structural damage to mounts and driveline components without an external strike?


2. What specific wear patterns or marks on the piston face, propeller blades, or shaft should we inspect to definitively prove the failure originated INSIDE the engine rather than from an external strike?


Thanks in advance for your time, technical expertise, and shared experiences!

 

[fallguy]

My experience is null.

Submit a picture of the prop damage. Minor distortion of the prop versus a clear ding are pretty straightforward. The leading edge(s) of the prop would not be damaged from the engine failure.

 

[jehardiman]

A month ago, after weighing anchor and stowing fenders, I was accelerating slowly out of a beach area. Right at the moment the turbos began to spool up and build boost, an extreme, violent vibration occurred in the port engine. I immediately pulled the throttle back to idle, and the engine shut down completely.


Key point: At the helm and throughout the vessel, NO impact, thud, or collision with any submerged or floating object was felt.

Welcome to the forums

The damage didn't have to occur while underway. It is possible to have damaged the prop or shaft many ways while moored in a shallow area. A bent prop or shaft will cause almost all the damage listed when throttling up to speed... and some of the damage listed can only be caused (on a properly sized shaft system) by something outboard the engine (i.e. an internal engine component failure will not backdrive and twist a proper prop shaft....the piston/rod/crank/block would fail first). As for the rest...what does the timing gear/belt look like? Extreme vibration will cause tooth jumping/damage which can make the engine eat a valve and destroy the piston and head with the turbo eating the loose pieces. Minimal damage/misalignment to the timing gear means you have only one piston involved per your hypothesis.

The only other failure to cause both the internal and external damage stated and huge vibration after startup is the loss of the engine-to-shaft geometry (i.e. engine mount failure)...but then the gears should be damaged but not the propeller unless the tailshaft got thrown.

As fallguy says...photos of all the parts.

 

[baeckmo]

The damage of the Vulcan coupling and the engine mount/bracket may be the key to understanding, as it probably will show which direction the overload torque was applied. If the engine stopped and the prop kept rotating, you have one failure mode, if the prop stopped and the engine thumped on, you have it the other way around. NOTE: when dismantling, don't "clean up" the parts before inspection!

 

[HelmutSheina]

Surely impact damage is claimable on insurance?

 

[gonzo]

There is no way an engine failure would damage the propeller as you describe. Since the turbos had not spooled up, the engine was at relatively low RPMs. What gets my attention is the description of the anchorage; a beach area. However, a grounding and the internal engine damage would not be related. There are damages that may be also caused by lack of maintenance. A broken mount will cause misalignment and could bend a shaft, but would not damage the propeller. I am an accident and insurance fraud investigator. The physical evidence has to be consistent with the story, which in this case isn't. Are you trying to get a mechanic to take responsibility for the damage? Any investigator would agree with my assessment. I have seen way too many claims invalidated by people not wanting to admit they did something foolish. In short, the story and the physical evidence do not match.

 

[fallguy]

Surely impact damage is claimable on insurance?

Perhaps with a large deductible of a percentage of the claim.

It could also be that the OP just doesn’t want to repeat.

The idea hitting a rock something causes internal engine failure is rather difficult for most anyone to appreciate. And I feel the pain for the OP.

Perhaps @gonzo could explain it best, but the combination of hitting something and accelerating the turbos perhaps created an ideal catastrophic condition. For many boats, the hull squats at rev and I have personally experienced finding bottom this way even in a small skiff.

So the engine revs, the hull squats a bit and the prop finds bottom. Hard sand bottom may not offer significant trace of impact. I made a nav error one time on a long trip and got super lucky as the boat hit hard sand bottom. It was a good thump, and almost zero damage but some paint on a painted prop on outboard. I had come off throttle so hard as the boat came down a bit it was the opposite of what happened for OP.

This is one reason to always idle out to the channel I’ll add.

 

[gonzo]

If he had run aground, which he denies, the engine would slow down and the turbo would've never spooled up. Hard sand would not be likely to bend a propeller, bend a shaft, and break a motor mount. Also, the OP does not show any photos or state the previous condition. Motor mount may break if they are old. This seems like someone fishing for an alternative explanation to get a free repair. I have investigated hundreds of them.

 

[jehardiman]

The damage of the Vulcan coupling and the engine mount/bracket may be the key to understanding, as it probably will show which direction the overload torque was applied. If the engine stopped and the prop kept rotating, you have one failure mode, if the prop stopped and the engine thumped on, you have it the other way around. NOTE: when dismantling, don't "clean up" the parts before inspection!

+ for the coupling and mount being the important info.
++ for not touching the parts. I and my wife (then a navy shipyard metallurgist) have seen several failure analysis messed up by people trying to fit the parts back together during disassembly and inspection. She trained me so well that the time something happened on my watch (a rigging component failure) I had the divers bring the parts to me, and only me. I then covered the fracture surface to prevent follow on damage while shipping it to the lab. She later said that the cleanness of the fracture surface allowed the intergranular corrosion to be traced (wrong cotter pin material) and the cup and cone surface of the tension failure to be seen under microscopy.

 

[fallguy]

If he had run aground, which he denies, the engine would slow down and the turbo would've never spooled up. Hard sand would not be likely to bend a propeller, bend a shaft, and break a motor mount. Also, the OP does not show any photos or state the previous condition. Motor mount may break if they are old. This seems like someone fishing for an alternative explanation to get a free repair. I have investigated hundreds of them.

He said the turbos spooled and then he heard the thunk.

 

[gonzo]

He said they were starting to spool. The story makes no sense.

 

[baeckmo]

I don't think we should dismiss the OP's description of the events; it is what is noticed on the bridge, nothing more. It does not confirm one or another hypothesis, and until we have seen pictures of the damaged coupling, engine mount and bracket, it is not possible to draw any conclusions. The damage to the turbo is a consequence of the valve damage, which causes pulsating backflow to the compressor and disturbed flow to the turbine. But that is the only conclusion I'm prepared to draw from the OP's text.

The OP asked if we have experience from similar "sudden deaths", and yes I have seen some of those. Personally I'm not convinced that the prop and shaft defects are directly related to the engine break-down; the first questions on that theme are: has shaft line-up been checked, what is the gear ratio, is the transmission ok? I'd also like to see the broken valve cover outside and inside, plus the push-rods and valve lifters (hydraulic valve clearance adjustment?) etc. Next I'd check camshaft timing and gears in the search for cause of broken valve stems.

 

[gonzo]

He also has a broken motor mount. That may damage the coupling and maybe even bend the shaft. However, he has a damage strut and propeller. It is easy to determine if a motor mount has been damaged recently or is an old problem. A damaged propeller will not result from a turbo failure. That is where the story and the physical evidence don't match. Also, he says that the turbo was just about to spool, so the speed was moderate to slow.

 

[baeckmo]

He also has a broken motor mount. That may damage the coupling and maybe even bend the shaft.

Question is where you have the Vulcan; is it between engine and gear, or between gear and propshaft? In my world, I'd expect it in the first position, and if so, it is not linked to the broken engine mount. In that case the broken mount might be the result of bad shaft alignment (which could be linked to both bent shaft and worn cutlass bearing). With "normal" gearing, the rotating momentum of the prop (at low rpms) is too small to damage a coupling either side of the tranny, but a dead stop of the engine is worse. Again, show us the pieces, mr OP!

I agree with Gonzo on most of the rest of the findings and what I don't like about the "story" is the question #2, where OP wants proof of his hypothesis before reviewing possible alternatives and before showing us the relevant imaging we asked for. The description of the break-down event, as noticed on the bridge however, must be accepted as the laymans observations. When one arrives at a "trouble-scene" for trouble-shooting it's important to register all info available, and then to ask "what info is missing, and what is at odds with physical evidence"?

The trouble-shooters manifesto:

--ALL MEASUREMENTS ARE WRONG
--ALL CALCULATIONS ARE WRONG (EVEN MY OWN.....)
--ALL MATERIALS ARE ELASTIC BUT TO VARYING DEGREES
--ALL LIQUIDS CONTAIN VARIOUS AMOUNTS OF FREE GAS
--ASK "THE LAST MAN ON THE BOLT" FIRST
--ALL AND EVERYBODY INVOLVED ARE LYING, EITHER OF INNOCENT IGNORANCE, OR BECAUSE THEY SCREWED UP SOMETHING SOMEWHERE

 

[montero]

You wrecked the clutch after the impact.
The engine revved up and broke down.