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Detroit Diesel 12v92 burnt valves

lild62992

New member
I work at a place that has 8 or 9 tug boats running 24 hours a day. We keep having a re-occuring burnt valve problem on the DD 12v92 series engines. Any ideas?
 
Lots of possibilities come to mind. You indicate this is happening on more than one engine.

First, how the valve rockers and valve bridges are being adjusted. Is the same guy/shop doing the work on all the engines that exhibit problems? Could be something as simple as bad technique and or wrong clearance specification being used.

How well the cooling system is maintained can be HUGE for these high temp exhaust valves. They don't have long to transfer heat while seated and scavenge air can't entirely do the job. Internal coolant passages in the heads need to be kept clean and free from excessive deposit/scale buildup. 1/32" mineral scale is equivalent to about 2 1/2" of iron insulation factor for heat transfer resistance. If you are seeing more damage at the inner or "middle" cylinder's valves, this would be something to seriously consider as a root cause.

Any recent engine work on these such as head work or camshaft replacement? A machine shop could be setting you up for failure with a bad cam grind or poor valve to seat interface.

These engines don't actually "jump time" but can be assembled out of time and the valve timing can also get skewed due to extreme gear wear.
 
I would have to say that the cooling system is not getting the attention that it deserves. What do you set your valves and injectors with? Do you have any recomendations for removing scale out of the engine? How do you set the rocker arms? The help is very appreciated, thank you.
 
We are talking about newly rebuilt engines and older, but still don't have more than 20000 hours of service on the older ones. We are also using Deisel kleen with ctane. Would that be giving us a problem?
 
20,000hrs or 2,000hrs?

The valve bridges have to be adjusted/checked off the engine, in a vice or holding fixture following the procedure outlined in the service manual.

Your question suggests to me that you are either in management or you are a new tech to these engines. Either way, you need to understand that these engines require some special tools and knowledge to be properly tuned. Not rocket science by any means, but following the service manual procedures is essential to prevent wasting fuel and engine damage. I can't "walk you through" it here because mistakes would be made.

Not familiar with the fuel additive Diesel Kleen but I am assuming it is an algae-cide of some sort. Over use of these products, especially those containing alcohol, CAN cause problems.

Your cooling system maintenance will depend a great deal on the strategy being used IE: keel raw water or closed pressurized with the latter being easier to maintain against scale buildup within the engine itself. The proper selection and application of coolant, coolant additives and filters in the closed systems can go a long way to enhancing the trouble free operation of the engine. Preventing scale is much easier than removing buildup from a neglected system although there are some effective chemicals for cleaning. My experience with raw water flushing is somewhat limited though.
 
It was 20'000 hours. I have been working on them for about 3 years now and what I have learned about tuning the engines was just passed on by watching someone else do it. I feel pretty confident about doing though at least the valves and injectors. We don't ever mess with the valve bridges because they are factory new heads that have been pre-adjusted although I will be checcking them now. I was merely picking your brain to see if you would tell me something different from the way I have been taught.

The fuel additve is made by Power Service its called Diesel Kleen with cetane and slick diesel. We have talked management into not using it for a month on 3 boats to see if it makes a difference. They said it saves 600 dollars a day on fuel cost per boat so they didn't really want to do it.

The cooling system would be a good assumption except the engine pretty much stays at 180 degrees except in the summer time then they do run a little hotter but we still have problems year round.

So far since last April we have replaced roughly 32 heads on these engines. I just think that is too much trouble for them. They should be more reliable than that.
 
Wow! $600 a day! Why, that should be called "Magic in a Can"!! Lets do the math: 600 X 31 = $18,600 a month! That's about a 1/4 million$$ a year for a 24/7 outfit. A real BEAN COUNTER's dream! Do you know how many DD 12V cylinder heads that buys? No wonder they don't want to stop using the stuff.

Don't get me wrong, I looked this company up and they seem to be a reputable manufacturer with some fairly decent consumer reviews. The fact that you don't mention injector failure probably indicates that, at the very least, the juice isn't harming them. It's just that many of these "performance enhancers" aren't "woodsheded" (researched) very effectively by the fleets that use them. Thorough and accurate maintenance records aren't kept so that, when a problem like the one you're having crops up after application of the "miracle cure", you can go back and see if the use of the product might be a potential cause.

In addition to that, these products are usually purchased and stored in bulk and then are left to be applied by the least experienced and knowledgeable maintenance employees with little or no monitoring. The results are that the possibility of product contamination/dilution, over/under use and theft is later found to be a problem. Data is key when making blanket statements like "it saves us thousands". The problem is, there is usually little to no data to be had. These products find their way into large organizations all the time because some "higher up" got a lifetime supply for his Power Stroke toy hauler.

My next installment will be on your "brain picking". Gotta go for now.
 
Hi lild 62992

Me again,

I worked on the 71 then the 92 then the series 50 natural gas and finally the series 40 and series 60 diesels as well as Cummins, Cat and Navistar. Capped that off with a 7 year stint as an instructor for mechanics for a large municipal transit agency...with a cherry on top!

As an instructor, I ran into a couple of recurring themes time and time again. One was; "I've been doin' it this way for 30 years, boy!" To which I would sometimes point out; "Great! However you've been doin' it incorrectly, sir!"

The other popular one was, when I would ask someone why they were botching a particular procedure with such skill and grace, they would frequently respond with "well, that's how old Buck showed me". Of course, old Buck had been doin't it that way for 30 years.

My point being, make sure you are doing what's necessary for being successful, not what somebody else did a fore ya.
You most likely are adjusting the valves and timing the injectors properly but if you aren't checking and making sure the bridges are set correctly, you're boochin' the pooch. Relying on another guy or shop or factory to do that for you is not going to yield good results each and every time. No way those bridges should ever get out of adjustment but I found them that way all the time. I wonder how that happened?

You obviously care about what you're doing or you wouldn't be asking. I assume you have a service manual and do some self study. If not, get one and give it a once over. It's a far better teacher than old Buck...or me. They used to give us some good training but now days, I think they just throw you out there and expect you to swim.

20,000 hours on an engine, in my world, is a bunch. Not unheard of but that is the equivalent of over a million miles in a truck. The dirt stuff doesn't last nearly that long but on the water, maybe.

At 32 heads in a year, you guys definitely have a problem. A key phrase here would be "failure analysis".

Carbon build up from poor combustion...low operating temps?
Overloading?
Over fueling?
Weak valve springs?
Improper adjustment?
Poor exhaust routing/manifold leaks?
Inferior components?

I'm afraid I can only ask more questions. Your company would do well to get you some help, in person, figuring this out.
Good luck.
 
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