Mtu 396 TE piston problems

Hi,

Yes, based on my own experiences with MTU I would say this is a very good way to tell as long as the readout is accurate.

Do you have access to an MTU Dialog Unit?

Hi,

The suggestion is not bad and does make some sense as the compression in the Cylinder ( combined with the piston rings moving to the top of the groove as the piston changes direction at TDC) does actually pump Oil from the top side of the rings to the bottom side where it carries away some of the waste of combustion ( Carbonaceous Material, Acids etc).

If it were my engine I would just like to know why all the valves went bad so fast and far.

Does the boat sit in the winter without running?

Bad combustion - carbon residues

A good idea at every refuling is to take two fuelsamples, if supplier is a barge, two samples from every tank he's fueling from and seal them with signature of supplier and save them for later if trouble arise. It has happen on several occasions that fuel is contaminated with all sorts of rubbish, ie. old lub. oil, sludge or whatever they want to get rid of. I had to replace all liners due to excessive wear in a big 2-stroke engine in less than 5000 hours due to fuel problem. Normal lifetime on diesel up to 100.000 hours, on heavy fuel ab. 50.000 hours.
This could also have influence on the valves.

Except to visually check for contaminents before fueling I don't see the value in this. I sincerely doubt you'd be able to assign liability 1,000 hours later.

A thousand hours is only a few weeks of running. For the type of engine and operation he is talking about, fuel samples are very much an important part. They are required by law, the fuel is tested onboard, and a sealed sample is legal evidence when damage is claimed and proving the damage is easily done as there is a great deal of experience and knowledge concerning the operation of those engines. Visual doesn't count for much since IFO and HFO are opaque and MDO is often very dark.

Combining 2 posts to save bandwidth ....

The type of carbon fouling above the compression ring mentioned earlier tends to polish the liners and increase lube oil consumption more than cause mechanical damage. Anti polishing rings are now commonly installed in the liner to prevent carbon buildup on the piston to prevent this. The symptoms sound like overload, not fuel. I would tend to discount fuel because yachts don't typically upload bunkers from separate sources to separate tanks and feed engines from separate sources and no problems have been indicated by the other engine.

If the problem is not overload then I would go back to poor scavenging. Is the scavengine air pressure correct for the rpm and load? Did the failed valves show signs of tuliping and/or cracking? Any pieces missing from the edges of the piston crowns? Was the liner damage scoring or pitting as from micro siezures?

Thank you marmot. Learning a lot on this thread.

Marmot, I run a lot of yachts and a lot of yachts do tend to fuel from different sources and fuel different tanks and transfer it. There are numerous times when I may run 2 fuel tanks down and still have 1 or more that is full or near full and may not fuel it or may only put in 5-10% to top it off. When travelling, you'll take on fuel from a different source every single day. It's actually very common on many yachts from 50' + to do this. I was on a 97' and we held 6000 gallons between 4 tanks (1500gal each), along with 2-125 gallon day tanks. We never fueled all 4 tanks from the same source. Chances are we ran two down and topped them off and then ran the other two down. So fuel can be an issue. I know the dealer would take a fuel sample from the secondary filter and an oil sample from the oil filter. from the subject motor before rebuilding anything. As cheap as it is to do a fuel sample, why not do one just to rule it out? Water in the fuel can split injector tips and do this type of damage also.

As for replacing 10 cylinders and liners, I would recommend doing a major overhaul if you're getting into it that deep and replacing all cylinders and liners, checking the heads (even though they were recently rebuilt) and having all injectors checked and flowed. I have had 1 injector split the tip and washed out a cylinder liner. The piston looked exactly as you described, it was clean in 4 round areas where the excess fuel washed the carbon away. It didn't get into the oil or we didn't notice the level raise, because it was a 2 stroke diesel (12v71TI) and I guess it all went out the exhaust. I can pull up the photo of the piston and liner if you're interested in seeing it.

Condensation can also do a number on the valves and seats if the vessel sits all winter and is not started and run up to temperature at least every 2 weeks to get oil up in the valve train and burn out any condensation.

Hi,

Can you please explain the above rather ambiguous statements?

Isn't this what I posted in the Temp or Life of a DD Engine?

10 of 12 out of 12 or 10or 12 of 16 would indicate that this is a fairly major overhaul if nothing else.

Have you ever seen an excessive Centistoke injection stream?

Sitting has been mentioned at least twice before in this thread so thanks for the support. Unless you run your diesel at a reasonable load you will make nothing but water vapor by just starting and stopping them

If you're going to replace 10 liners, might as well do them all, check everything and remedy the problem. It could be defective parts of some sort.

I have no idea what an excessive Centistoke injection stream is. Is there another name they might use here in the US? Water or detonation could hammer the valve seats as well as do many other bad things.

Getting the engine up to operating temperature without a load will still burn off any condensation in the upper end of the motor (inside the valve covers etc). Heat is heat, running it under a load is better for the Turbo's and whatnot but it doesn't sound like that is feasible where this boat sits.

"... shine spots on the crown?"

Are you seeing this on all the damaged pistons? If so then you may have the wrong tips, wrong popping pressure, or even a timing problem. You wrote that the injectors were "fine" but are they correct in all aspects? And are you certain the other engine is not suffering any problems?

Here's a real stretch ... Is your fuel system isolated between the engines, do you have two separate or no centrifuge, dual day tanks, separate manifolds so that the fuel supply and return is never mixed between the engines? Has the good engine never seen the same fuel as the bad engine?

"Getting the engine up to operating temperature without a load will still burn off any condensation in the upper end of the motor ..."

Since it's an MTU it won't even start unless it is pretty warm already, running it with no load will just produce water and blow it into the oil which will not get hot enough to dry and the underside of the rocker covers will be nice and moist as they cool off. It is better to leave the engine alone or keep it warm with jacket water heaters - in my humble opinion.

Hi,
Sorry for the confusion.
What I ment was that contaminated fuel - whatever it is contaminated with - could shorten lifetime of both liners, pistonrings and exhaustvalves considerable due to bad combustion. In the early 60-ties a normal runningtime betwean overhauls on exhustvalves was ab 2000 hours and on pistons 5000 hours, 20 years later we were up to 10000 hours on exhaustvalves and 15000-20000 hours on pistons due to better lub. oils and better material in valves and pistonrings. Liners liftime were the 50000 - 100000hours depending on fueltype. Here I'm talking about heavy low speed 2-stroke engines or medium speed 4-strokes. If You were unfortunate and got fuel with for example catlyst-fines in it runningtime could be just a fraction of that.
On smaller highspeed engines ab 300 - 400kW, 1800 rpm used for generators we were able to extend time between oilchanges from recommended 200 hours to ab 1200 hours just by careful monitoring and testing of the lub. oil with the good memory of enginemanufacturer.

Cheers

Block heaters would be a very good idea in this situation and it would help to leave them on all of the time. I still would run the engines every 2 weeks to keep the valvetrain lubricated and oil on everything. Otherwise sitting for 6 months without running in a saltwater environment and you could get surface rust on valves, valve springs etc.

"I still would run the engines every 2 weeks to keep the valvetrain lubricated and oil on everything."

That is what the prelube pump is for.

Keep the engine warm and run the pump once in a while beats a cold start attempt and filling the engine with condensation from an unloaded run.