Engine problems

[jimm1009]

This is for the most experienced multi-fuel mechanics.

I think that I have a rod starting to knock. It is most pronounced at around 800 to 900 RPMs when hot. The engine also developed a bounce in the tachometer at the same time the knock became noticeable.
I now believe that I abused my engine during the recovery mission in May of this year while driving it the 240 miles home. After reading several posts, I pushed the truck too hard and probably shortened it's time to overhaul but I will wait for your comments before doing anything else.
The engine is still installed, and starts with no problem. It has the typical gut-wrenching 15 to 20 seconds before oil pressure (have mechanical unit as redundant gauge for a while in addition to OEM unit). I do plan on installing the spin-on adapters with anti-drain back filters soon.
Since there are no rebuild tags on this engine and it has almost 29,000 miles on the odometer, can I get away with new standard rod bearings or should I pull the crank and have it turned and do the mains too?
If I can install new / standard rod bearings now without having to remove the crank, can I drive it for another 2000 to 4000 miles (or more) before pulling the engine for a complete overhaul?
Obviously this all depends on what I find after dropping the pan but I am basing these questions on "averages" for the average engine with 28,000 with average operation and average care over 15 years or so.
My engine was manufactured around 1991 so it is not the original serial number engine installed during truck manufacture.
Any recommendations on parts would also be greatly appreciated.
6 rod bearings and pan gasket as a minimum.
Do you know what the published time frames are for replacement of components on these trucks? Most vehicles have a "schedule" of removal and replacement of components but I have never seen anything published anywhere.
I do have all the TMs for parts and maintenance and I have a lot of experience with 6.2 diesels and older 4 & 6 cylinder jeep engines but this is my first medium engine experience.

Thanks in advance,
Jim jimm1009@yahoo.com or PM me here on S.S.

 

[DDoyle]

Since there are no rebuild tags on this engine and it has almost 29,000 miles on the odometer, can I get away with new standard rod bearings or should I pull the crank and have it turned and do the mains too?
If I can install new / standard rod bearings now without having to remove the crank, can I drive it for another 2000 to 4000 miles (or more) before pulling the engine for a complete overhaul?


Do you know what the published time frames are for replacement of components on these trucks? Most vehicles have a "schedule" of removal and replacement of components but I have never seen anything published anywhere.

As to the first - I'd Plastigage the rod bearings. If you are not familiar with this product or its use, just Google - or go by NAPA. But before that I'd check the timing of the injection pump - while the chance that this is the source of your trouble is remote, checking it is so relatively easy compared to the amount of labor you MIGHT save its hard to pass up this easy check.

If the truck has 29000 miles on it I'd be shocked if the engine had not been built. I have seen the averages for time/hours in service of these engines, and its relatively short (probably due to the military procedure of swapping engines rather than in-truck repair for many problems.

HTH,
David Doyle

 

[Recovry4x4]

I'll add that I don't think there is a flat rate book for these.

 

[Ronbo]

I dont mean to change the topic but whats the most miles someone usually gets outa one of these? Like any other diesel ?500k?

 

[DDoyle]

I dont mean to change the topic but whats the most miles someone usually gets outa one of these? Like any other diesel ?500k?

Nope - more like a gasoline engine - that is what the design started as. I've not heard of anyone putting over 50000 miles on one. But then, who but Uncle Sam would push one of the hot, rough riding, but great trucks that far!!

 

[beaubeau]

I would be sure to find where the Nock is comming from. It could be Nock from the IP . or even in the clutch assm. What is you oil preassure running? Does it nock right away when you start it? These engines are as good as the person running it. The Life span is short in Millitary because guys who run the run the Crap out of them and don't care what happens.
If it is a Rod, find out what one it is before you take it apart. Inspect the crank and Con. rod to see if the bearing Spun. IF all looks good, just put new Standard bearings in and rod bearings. Good luck, and keep us Posted, Phil

 

[jimm1009]

My oil pressure is about 60 PSI above 1500 RPM and then drops down to about 30 PSI at idle.
What part of the clutch would be nocking? I've not heard of this.
It does seem to be a little low on power.
Could this be related to the I.P. starting to show wear?
I'm not sure how to inspect the I.P. or the clutch for anything that would cause a nock similar to a worn rod bearing.
Jim

 

[m35a2cowner]

Engine knock

With the engine good and warmed up try loosening the injector lines one at a time on each injector. If the noise disappears on one cylinder you have found the problem. It might be an injector problem (poor spray pattern) causing the noise. If your not familiar with engines you might be money ahead to take it to a trustworthy (ask around parts stores, other truck owners, BBB etc.) mechanic. Engines in these trucks are a lot louder than civilian models. Might be a remote chance noise is nothing to worry about, or something other than an engine noise. Say a failing air compressor or water pump for starters. Good luck

 

[m16ty]

You can find out if it's a rod knock by performing a simple test . Start the engine and listen for the knock and watch your oil pressure gauge. When the oil pressure starts to come up if the sound of the knock changes you more than likely have a rod issue (or at least a oil lubricated part). If the sound doesn't change I'd look somewhere else. It could be a number of things that could cause a knock. You can also take a long screwdriver and hold the handle to your ear and touch the blade to different areas on the engine and you can usually pinpoint the general area of the knock.

 

[garp]

Pull the oil filter and cut it open. Look for metalic debris from a failed bearing. cut a strip of the filter paper out and wrap it in a shop towel, squeeze the oil out in a vise and you will be able to see any foreign material in the pleats.

 

[desertfox]

Everyone that has responded has provided you with excellent ideas of trouble shooting the problem. Using the long screw driver is an excellent but cheap stethascope. Have used this for many years to locate a problem.
If you have a tag on the engine dated 1991 then it was rebuilt in 91. I believe the last engine manufactured was 1987. This is the latest casting date I have seen on engine blocks. The casting date will be located above the starter
Correct me anyone if I am incorrect?

 

[m16ty]

Everyone that has responded has provided you with excellent ideas of trouble shooting the problem. Using the long screw driver is an excellent but cheap stethascope. Have used this for many years to locate a problem.
If you have a tag on the engine dated 1991 then it was rebuilt in 91. I believe the last engine manufactured was 1987. This is the latest casting date I have seen on engine blocks. The casting date will be located above the starter
Correct me anyone if I am incorrect?

From what I understand the EPA granted the gov. a one year waiver for 3,000 engines in Sept. 1987 so '88 should be the last year. I've got one engine in my deuce and two spares. The one in my trucks is dated '84 on the ID tag with a rebuild tag under it that is dated '92 with rod and main journal info filled in. The other two engines don't have a rebuild tag with one a '87 on the ID tag and the other '88 on the ID tag. I didn't know about the casting date on the block. I'll have to check that out.

 

[FreightTrain]

Go to Blackstone Laboratorys and order a oil sample kit.Drive the truck a little,get it up to temp and take an oil sample.There is a valve on the drives side of the engine behind the filter cans.That will tell you exactly what is going on.Only cost about 20 bucks.Could be a rod bearing,Wrist pin pulling out,injector stuck,burned valve,Air compressor going out,pressure plate comming apart,Injection pump failing,Hard line cracked,Hard line rattling around,Fender rattling around,etc.Your mains bearings are fine I can say that for a fact.

 

[DDoyle]

I once bought a truck from DRMO (this was long before GL) that had the pump a little out of time (one tooth, IIRC), which caused a preignition knock, which was loud at certain RPMs.

To answer your question, it is likely not the pump itself that is knocking, but the fuel delivery that is causing the knocking (unless it is in fact worn reciprocating parts in the engine as you suspect from the get go).

Happy hunting!

David Doyle

 

[Stretch44875]

It's also not a big deal to pull the oil pan and check for play in the rods. May have to lift the frame of the truck and let the axle drop to get enough clearance to remove the pan. I've had one off and on in under 2 hours.

 

[Blacksmoke]

Just out of curiosity, what did you do on your way home that makes you thinks you ran her too hard?

 

[jimm1009]

What is now what I think that I did wrong is that I drove it between 54 and 56 miles per hour for about six hours.
I never passed the red line but I have read from several others that 50 MPH is the fastest that you should push these monsters with the 9:00 x 20 tires.
The six hour run was not all in one stretch as my bladder could not last that long, but I never shut the truck off during the 8 hour period (6 on the road) and I was very observant of oil pressure and water temperature at all times. I'm very "anal" about those readings being an aircraft mechanic for purposes of putting food on the table.
Before departing Camp Shelby, MS, I spent two hours going over the truck checking all fluids, water, tires, etc.
Could I have punished the engine during this run by the six hours of 2300 to 2400 RPMs?
Inquiring minds need to know.
Thanks for all the wonderful information.
I will read up on timing the pump and I will try cracking the injector lines once warmed up since this is much easier than pulling the pan even though that is not a difficult task either.
I'll also try the long screwdriver but will probably invest in a stethoscope too as they sure are nice to have and not too bad in price.
Any more ideas will be much appreciated and if anyone knows of a good source for bearings if everything else pans out for me, please let me know.
I like to support NAPA but I do purchse from the parts dealers here on S.S. too.
Mucho Thanks!!
Jim

 

[jimm1009]

Engne problems

Information update on the Hercules installed by Uncle Sam
I looked at the right rear side of the block above the starter.
There are three rows of information.
Starting at the top: FSCM28265
2nd row; 11610199
3rd row; a design with oblong circle with a "M" in it with a small "c" below the M inside the oblong circle. Next is a large 46 and then in the cast tag is "KO18" just forward of the 46.

The data plate very clearly says " date of manufacture 4-91" and the serial number is 3999517.
There are no rebuild tags installed nor are there the holes for the rebuild tags to have ever been installed.
I agree that the "date of manufacture" is not correct and is should be "date of rebuild" or "date of re-manufacture" but it is odd that it does not have the additional rebuild tag as required by Depot Overhaul so that the next mechanic knows what size bearings and bore are now incorported.
Jim

 

[Big Mike's Motor Pool]

i dont know if running it for 6 hours at just below redline will hurt it. if it was a generator it would run longer than that at high rpms. maybe im wrong though.

 

[Jake0147]

What is now what I think that I did wrong is that I drove it between 54 and 56 miles per hour for about six hours.

Mine has done that more than once. It hasn't blown up yet. I'm not trying to rule out your judgement, but my experience leads me to believe that the only thing this could do is "hurry along" a failure that is already in progress. I don't think this created any failures in and of it's self....

Lots of good advice here. Westfolk pretty well summed up my thoughts as well. You say you've worked on some 6.2 engines, so you're probably familiar with the knock that fuel issues can cause? Don't rule it out without ruling it out. Also, don't rule out the "other engine" in the engine bay. Compressors can make a pretty good rod knock too.

If you're going to use the oil sample valve, be sure it's clean inside, and flush into a non-sampling container before you fill the sampling container.