Where do the 3116's fail

Where do the 3116's in FMTV commonly fail

Retitled

Where do the 3116's in FMTV commonly fail

These trucks are getting older and common failure points are bound to begin showing up as described below.
NOTE: Took this from another thread so not to hijack it.

JoshuaGrooms83 said:

...On a positive note, another LMTV I swapped the motor out of got picked up by the unit today and it drove out after being towed in One down, two more to go! lol we got another in last week probably needing a motor as well. its al the old 1083s and 1078s S&S or BAE trucks with the older CAT motors. That keep either breaking oil lines or cracking the gear covers by the air compressor. Keep an eye on that so you don't wind up blowing a motor. Our engines cost us about $40G to replace... and there arn't even new. The last one I replaced was crated and preserved back in 2008.

and no need to thank me, its an honor to serve and to continue to serving. But thank you

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Can you be more specific please as time allows?

I'm interested as well, as I have the m1081 which should be the same engine spec and m1078

There are a lot of 3116s in civ use. They get mixed reviews on the net. I read a lot of the RV forums with 3116 discussions and there are a lot out there with several hundred thousand miles on them still going strong. The 6x6 trucks have a 290hp 3116. This is top of the power range for that engine. It's not going to last as long as the lower power rated 4x4 3116. Clean oil and a properly operating cooling system along with looking the engine over for leaks or other signs of distress are good habits to prolong engine life.

Suprman said:

... read a lot of the RV forums with 3116 discussions and there are a lot out there with several hundred thousand miles on them still going strong. ...

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Gottya Will and much thanx.

In general the intention for starting this thread was to get more details on observations Joshua made about specific issues they are running across there at his command. Granted he may not have time to add more detail but hope so. These extra tid bits beyond the TM checks and General Checks that he can offer will strengthen our arsenal; improving our chances of being part of that 100's of thousand of mile and going strong group.

Unfortunately I can speak from experience about the gear housing cracking where the air compressor mounts on the 3116.
When I purchased my truck (1994 1078 ) several months back it had an oil leak at the compressor. Originally I thought it was just the gasket but when I tore into it I found the gear housing was cracked between the upper and lower compressor mounting bolts. I also found the bracket that supports the rear of the compressor was cracked. My guess is the bracket which supported the rear of the compressor became loose and eventually cracked thru where it supported the compressor. This then led to the compressor only being supported by the 2 bolts at the gear housing which eventually cracked.

The yellow painted casting (gear housing) directly in front of the compressor cracked near the top bolt (The picture shows the replacement gear housing in place)



My suggestion is to make sure the 3 bolts holding the support bracket (green bracket in the below picture) to the block are tight as well as the single bolt from the bracket to the compressor.



Note: My bracket has been modified to reinforce the area that was cracked by welding on the extra reinforcement

If the gear housing gets cracked, in order to change it everything needs taken off the front of the engine as well as the compressor, fuel governor, oil pan, radiator removed and camshaft removed. I just got mine put back together and expect to be back on the road soon. Based on this experience I used loctite blue on all of the critical fasteners.

I will be keeping an eye on these fasteners as well as the starter bolts that others have mentioned as being loose. If anyone needs more details or pictures let me know.

Smike740 said:

... If anyone needs more details or pictures let me know.

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Pics are always great to help folk wrap their mind around discussions. If you got time would certainly be appreciated.

Seconded. Post em up!

Ok I will post some photos this weekend

Still runs. Minus a cylinder though. And it was a recent military reman motor. I have no experience with cat internals. No sleeves no good. If it was a Cummins I would pull the head and get into it.

Suprman said:

[Image] [Image]...was a recent military reman motor. I have no experience with cat internals. No sleeves no good. If it was a Cummins I would pull the head and get into it.

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What da heck happened to that? in a flood? Hope to hear that's a rare occurrence damaged engine.

Looks like coolant came up around an injector. I believe there are coolant paths around the injectors and o rings to keep it in place. This is info I found searching the net though. I don't know about cat motors.

I updated my original post with pictures.

Also regarding the oil line, the previous owner mentioned the oil line failure. The line goes between the cylinder head and the rear of the fuel governor. My truck has the hard line replaced with a high pressure hose. See the below picture. I am not sure why the metal line would fail but it's probably worth inspecting.

Smike740 said:

I updated my original post with pictures.

Also regarding the oil line, the previous owner mentioned the oil line failure. The line goes between the cylinder head and the rear of the fuel governor. My truck has the hard line replaced with a high pressure hose. See the below picture. I am not sure why the metal line would fail but it's probably worth inspecting.

View attachment 636108

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is this a picture of your truck? There is both a high-pressure hose and a hard line in the picture so it is a bit confusing.

Yes, the hard line you see is the fuel line, the high pressure hose replaced a hard line which is an oil line. As I said I am not sure why it would fail but the previous owner said it failed and his mechanic installed the high pressure hose.

Most of the bad press the 3116 has gotten stemmed from a number of defective blocks that were put into boat engines (350hp). Caterpillar took care of all of those under warranty. There have been exhaust valve failures on those same engines, but guys in the know tend to relate that to clogged heat exchangers and people running them WOT for hours on end in large heavy hulls. The smaller boats didn't have much of an issue with the 3116. I've seen studies that showed engine failures in trucks and RV's are statistically rare and aren't significantly higher than any other engine of it's size.

The 3116 350 horse was only installed at manufacture in pleasure and recreational craft. All commercial watercraft generally got the 315hp or 290hp versions.

The 3116 does have a rather restrictive exhaust side of the head which causes that area to get hot, hence the valve problem on the marine versions.

Funny that the unit said new wasn't available anymore.. I've seen several new one 3116's sell over the past year.

I believe that coolant leaking from an injector is a seal problem due to an injector that is not properly seated it's mentioned in a number of forums.

As far as busted oil lines etc, I don't know any engine that will last very long when all the oil in the sump is pumped out of the engine through a broken line, those would probably be a good thing to replace due to age.

Everything cat is expensive I didn't want to get into that motor for any more money. if it was a simple fix like new o rings on an injector I would probably attempt it but it's not my area of expertise.