Multifuel engine life

Found this in an official document:

"Though not a maintenance fault, failures of multifuel engines created the requirement for a major off-shore maintenance effort and a sizeable supply problem. In January 1967, more than 300 5-ton trucks were deadlined in Vietnam because of inoperative multifuel engines (a similar condition existed for 2½-ton trucks) due to cracked blocks, blown head gaskets, valve stems and connecting rods. A study indicated that many failures occurred between 9,000 and 10,000 miles and that the units hardest hit were the line haul transportation units whose engines were subjected to continuous use (2,000 miles per month in Vietnam). The prospect for improvement at this point was negligible because of the lack of repair parts and overhaul capacity. Multifuel engines powered both 2½- and 5-ton trucks. A similar condition also existed in Thailand. The annual engine replacement rate of 6 per 100 vehicles per year increased to a rate of one engine per vehicle per year.

By the summer of 1967, an airlift program, Red Ball Express was put into effect in an attempt to alleviate the shortage of engines and repair parts. The Red Ball Express was designed to be used in lieu of normal procedures exclusively to expedite repair parts to remove equipment from deadline status. Reserved and predictable airlift was made available for this purpose. The seriousness of the situation led to a multifuel engine conference on 28 August 1967. The conference resulted in several recommendations, the most significant of which was that three multifuel engines, LD 427, LD 465, and LDS 465, were to be placed under Closed Loop Support management because of the inability of units in the field to cope with the maintenance problem. A further recommendation was made that return to the Continental U.S. be authorized for vehicles that could not be supported with multifuel repair parts or replacement engine assemblies. Because a large percentage of the producers' production capacity was consumed in end items assembly, some repair parts and new replacement engine assemblies were not readily available. Department of the Army approved the recommendations of the conference and directed that necessary retrograde, overhaul, and shipping operations be initiated immediately.

Although the conference had focused attention on the supply aspect and premature failure of engines, significant intangibles remained unsolved, including proper operation of vehicles and user maintenance. Because of the characteristic difference of the multifuel engine from the standard internal combustion engine, periodic maintenance and specific mandatory operational procedures differed sharply from procedures used with other vehicles and required closer attention. Simply put, despite years of testing effort, the multifuel engine did not possess the ruggedness and tolerance to withstand the abuses inherent in field operations."

hope this is interesting to ya'll.

Regards,
David Doyle

I would think a heavy duty diesel should run at least 250,000 miles. Are the later LDT engines any better?

I always knew they were a crappy excuse for an engine, but 10,000 Miles? Good lord!

The engines are an excellent design but the weak link is the 22:1 compression ratio. Where most diesels run at 16-18:1, the MF ratio had to be increased so it could burn multiple fuels. This makes the engine susceptible to damage when lugged or over reved. When a machine is overtaxed something will break. Add inexpirenced and uncaring operators and the engine is doomed. Even today I see people drive them as though they were gas engines. All diesels need special care and operation.

see below

I've always like the Multifuel - and still do.

The foremost thing to remember here is that, per other documents I've recently uncovered, many of these trucks were given NO regularly scheduled preventative maintenance. This was in large part because there were far too many trucks, and far too few mechanics, and far too much cargo to move. Any truck that could move was dispatched, and only those trucks immobile were given attention by the mechanics. Even leaking radiators were not sufficient reason to deadline vehicles at this time.

The trucks were also often grossly overloaded, and operated in conditions that most of us really cannot comprehend. Frames frequently broke due to overloading and operating at speeds too fast for the road condition - the later being defined in the documents as speeds over 20 mph. Think about the condition of a road that will break a five ton frame at 30 MPH!! A chain was usually snaked across the hood of five tons so that the left fender could support the right, which was prone to breaking off due to the load imposed by the air cleaner. Fuel tanks were often chained to the frame for the same reason. Oftentimes grades were such that by the time the summit was reached trucks were in first gear and low range - and wishing for deeper reduction. And remember, these were ON ROAD operations! Somehow I suspect the "how do I increase top speed" question that so often comes up on this forum do not often arise in Vietnam.

I doubt that any powerplant would give satisfactory service in these conditions. The Multifuel was relatively new and unproven at this time. The -427 had already been deemed unsuitable due to block and rod failures, and was being replaced by the LD-465 by the time the report above was published. The head gaskets were redesigned (twice) before arriving at the successful gasket we have today. I'll have to research the valve issue a bit later on.

None of the builders of the Multifuel classified it as a heavy duty diesel. Continental, the designer, as I recall, referred to it as a light duty diesel.

Best wishes,
David

Thanks David, as usual, you are a font of information.
This does give me some insight into what the lifespan of a multi-fuel can be. At 44,000 miles, I’ve already got what you reported licked. Since I’ve had to put in a clutch…I guess someone was riding it and the maintenance, while not as bad as Viet-Nam (and especially Iraq), was not what I’ll be doing to it.

If the muilts are so crappy why after 40 years are they still in front line use???

Yep
When I first went to look at my 5 ton , I lifted the hood and saw the Mack engine I said SOLD!!!
of course I'm sure I'll pay a pretty price for parts compared to the Multi.....Well thats if it ever breaks

The multifuel engine may be a wonderfull design, but it just wasn't solid enough to stand up to young, abusive drivers and no maintenance. The fact that it could burn almost anything poured into the tank was it's greatest selling point. My point in saying the multi was a crappy excuse for an engine was the fact that it was a light to medium duty engine replacing the old, heavy 6602 gas engine. Obviously the 6602 could only burn gas and the Mack was a straight diesel, but either engine could take abuse that left the multi dead in its tracks. And besides that, I knew I'd get some of you p.o.ed enough to send out the lynch mob.

Hahahah... way to go lacoda. Want some more rocks to throw at another hornet's nest?

Thank you David for those interesting posts. Certainly things to ponder, or in lacoda's case, and excuse to stir up a $&!# storm.

Matt

I love my multi, but I accept that it's lifespan is retardedly* short.


* Not sure that is a word, but if it isn't, it is now

Thanks David. I still love my multies and wouldn't switch because of past mistreatment.
Looking forward to drive the xm757 with a late design multifuel engine with extra features including the ability to run under water without preps.

Need to figure out why my FDC suddenly started to leak after 1,000 plus hours of good performance....

Hey FS, if you still have that engine and related parts, come high water or hornets nests, I'm gonna get up that way to get it this summer! I just might drag westy along if we can get a weekend off at the same time. And I won't make any more nasty comments about multifuels (I'm outa rocks)

In spite of the existence of the document shown by David (above), the Army selected the multifuel engine for the M656/XM757 series 8x8 vehicles.
The late 60's design included many changes, some part of the engines we now play with.
Here are some differences first used in the LDS465-2 (from what I can gather, designed for the 8x8 trucks, David, correct me if I'm wrong):

1) Partial load fuel control added to the IP to prevent engine from developing full power during transmission shifting.
2) New fuel filters
3) New fuel injectors. Opening pressure set at 3,050 to 3,150 psi.
4) Injector lines have larger inside diameter for increased engine performance.
5) Larger oil cooler.
6) New coaxial water pump and fan drive assembly to allow independent operation of the fan (stopping under water).
7) Five ring pistons instead of four.
Crankshaft has increase counterweghting and reduced clearances.
9) The new camshaft has improved lobe design and new timing events to decrease tappet loading and reduce overspeed failure.
10) Crankshaft oil seal in the front gear cover.
11) A dual chamber, twin flow turbo charger to provide proper air flow at all engine speeds.
12) Intake rocker arms are drilled for better lubrication.
13) New oil pump with larger capacity.
14) Exhaust valves and seats are new and improved.

wow that does sound like a bunch of changes. All for the better also, the only thing I dont get it 5 rings? if the cylinder pressure gets past the first one its over. The standered 3 ring goes as such.. lower oil control, middle oil scraper, top cylinder pressure. There is only ONE sealing ring. maybe to keep piston from hitting cylinder wall? is that a problen in the multi?

Bjorn, Can you take some close up pics of that turbo? And mabye of the tag too?

I'll be glad to.
Meanwhile, here is a picture of the LDS465-2 piston.

Surely would be interesting to see comparison's between all the variety of vehicles the military has and has had. Were the issues that the multi had unique because of the design...or are we seeing just as many failures with other mv's? Is the issue the maintenance, operation or design or a flavor of each mixed?

I got "issued" a brand new M998 in saudi the frist go round. Drove it there 200-300 miles at most. Return to Ft Hood and it got maybe a few 1,000's miles more. So no more than 5,000 at most. Motor pool called and said it was do for service to bring it in. I drove it there , it was running 100% nothing wrong at all. Left it at the motor pool. the next day they call and said it had to go to a higher level maintenance for a new eng. The water pump was bad. They showed me the "test" for this. The mechanic started it with the throttle to the floor it started spudered then died. He said that was a bad water pump and the eng needed replaced.
And they put a new eng in it