Mtu 396 TE piston problems

What is the condition of the turbos? Almost imperceptible loss of turbo efficiency can lead to overheating of exhaust valves and the kind of damage you described. Once you have some tramp metal flying around you are almost guaranteed to have more turbo damage as well.

Hi,

Have you had the Camera in your Stbd Engine?

Excessive Exhaust Backpressure caused by a restricted silencer etc can also have a pretty heavy effect on Exhaust Valves, you would normally see this in your EGT though.

I was on a boat with a pair of 16V 396 TB94's that were rated at 3520 HP.

We used to regularly see 800 Deg C in the Exhaust- we also had a number of B1 Turbo Charger failures.

I neglected to mention that a slight overload in combination with poor scavenging will combine to create the problems mentioned. have a good look at the prop or pump on that side.

By pump I meant the impeller if you are running a jet drive. It doesn't take much of a tweek to increase the loading of either. Ask K1W1 about his recent experience with that one ...

If the boat seems to be hanging up at the point where the power demand should drop off as it gets on plane it is staying in a high drag condition and that is where you are likely to sustain a slight overload and incur heat damage. I had that problem with a 396 powered jet boat There were nearly identical symptoms attributable to a middle aged weight gain ... the boat, not me.

"... shine spots on the crown?"

Localized high temperature burns off the carbon. This is consistent with overloading. I would check the accuracy of your EGT display.

Hi,

The loss of Valve Clearance is either the valves settling further into their seats and the heads or the heads about to pull off and stretching the valve stem there by sticking further out of the guides.

Shiny spots on your pistons in the area of Injection can indicate an increased viscosity of the injected medium and having it stick and burn on it's way across the Piston Crown.

Is your fuel good?

I know of another yacht with these engines that had similar problems and it was blamed on fuel quality by MTU.

"... it was blamed on fuel quality by MTU ..."

But this appears to effect only one engine.

Hi,

It affects one engine that he knows about, he said his last visual of the Stbd one was last year.

If it sits a lot the fuel could have gone bad also gummed up rings ( another symptom of too little use and exhausts open to atmosphere)on these things cause massive oil burn around the edge of the piston crowns.

"... he said his last visual of the Stbd one was last year."

You've got a point there. But, if the stbd engine was suffering the same problems I would think it would have shown up by now.

I too would check the fuel. On Many yachts one engine runs off of a different fuel tank then the other engine. I've seen where a marina in the NE (USA) was selling heating oil as diesel. I would have the fuel tested. Also check the vent for the fuel tank and make sure it is not clogged. If it's a load issue, I would think he'd be seeing problems with the stbd engine also, unless the tachometer is off and he's running the port engine 100rpm more then the stbd and dragging the stbd engine and running a much higher load factor on the port engine. It sounds like it may also be a fuel starvation issue of some kind. I would run fuel pressure gauges on both engines and verify proper fuel pressure. Water in the fuel will also do the things that are described. Clogged aftercoolers may also create a high intake or fuel charge temperature and create issues also.

I really doubt it is fuel if it only effected one engine over an extended period. Besides, bad fuel usually manifests itself in other symptoms that are visible to those who are looking.

A damaged or tweeked prop only effects the engine that drives it.

What is fuel starvation going to do to the cylinder components of a diesel?

"fuel charge temperature" ???