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Big Diesel
10-17-2012, 06:31 AM
Post: #1
Big Diesel
Here's another question out of the "Auto" category but I'm pretty sure the same principles of mechanics will follow. I also don't have all of the information on this one so I'm just looking for a general theory.

D355A Komatsu bull dozer. In-line 6, diesel.
This dozer broke the oil pump drive shaft, lost oil pressure & the only thing that the mechanics found wrong was that the turbo locked up. Fixed the oil pump, replaced the turbo & back to work it went. I don't think that it worked more than a day or two and it died backing down into the pit. We drug it out, tore it down & found the shaft broken again. This time a main bearing was burnt too. Replaced the bearing, shaft & the oil pump this time. Put it back in the dirt and now the oil pressure kept dropping. Normal on one of these is between 50 & 70 psi. At this time it was only holding about 45psi wide open, 20psi a half throttle & zero at an idle. Back out to the repair area, dropped the belly pan & oil pan again & tried another oil pump. No change. Put shims in the safety valve. This raised the "Cold" oil pressure to 75psi but after running for 5 minutes it went back to the same as without the shims. Put shims in the main pressure regulator valve. This raised the pressure to 70 for about 10 minutes and then back to the same as before. They tried a couple of other things like putting a gallon of "Lucas" in the oil also with no effect.

Any ideas of where to go next? Any ideas will be appreciated!

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Garner

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10-17-2012, 10:55 AM
Post: #2
RE: Big Diesel
Something is missing here. What made the oil pump shaft break? If it's long enough there's probably some sort of support bushings that are worn or the pump is starving for oil due to an air leak on the suction side causing it to lock up.

If the bearings are getting toasted there's a good chance the crank is in need if inspection at minimum. What about the cam bearings? The oil pressure is going somewhere and it's likely a wear issue from the oil problem that can't be fixed by throwing "some" parts at it.

How many hours on this beast? Is it due for a full bottom end freshening up? Does it have oilers for the bottom of the pistons and one of the nozzles is missing? (pissing away the oil pressure internally) Most commercial engines can go 5 - 10,000 hours between tear downs if the oil is changed on a regular basis so where does this one fall in that category?
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10-17-2012, 07:16 PM
Post: #3
RE: Big Diesel
Well, yes something is missing here. Quite a lot in my opinion. That’s why my second sentence says, “I also don't have all of the information on this one so I'm just looking for a general theory.”

Why did the shaft break? They claim that it is a common weak point in this engine and happens a lot. Starving for oil? They filled the suction lines with gas to see if there were any leaks. They checked gaskets and mounting points as that is also a common failure point on this engine. They claim that isn’t the problem either.

We know that the oil pressure is going somewhere and throwing parts at it won’t fix it. That is why I’m looking for suggestions on where others would look for the problem. You confirmed what I was thinking. We started tearing the top down this morning to look at the cam bushings. I didn’t think that the piston oilers (yes, it has them) would be the problem but I will suggest that to the boss. They are easy enough to check. I was leaning more to the cam due to the fact that it lost oil pressure several times. I figured that a bearing got damaged due to lack of lubrication.

I don’t know how many hours are on this since the last build. I don’t think that there is all that many. However, we don’t do a complete build unless it is necessary as it cost upwards of $30,000.00 for this small engine & triple that for a big one. The oil & filters get changed at 250 hours. This is the first time, in over 20 years that I know of, that we have had this problem. This is also the first time that I can remember of having multiple oil pressure losses. And I would guess that this will be the first time in over 20 years that the cam will be out.

I will let you know what the mechanics find in a couple of days depending on when they get it apart & if I get to talk to someone.

Thanks for using the forum,
Garner

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10-17-2012, 07:54 PM
Post: #4
RE: Big Diesel
Other things that come to mind are any oil lines that are internal to the engine. I have seen some that don't use conventional drilled passages but something more like small pipes that route oil to various moving parts. Then there's things like pressure relief valves behind the oil filter. Another thing might be a missing oil galley plug so the oil is just blowing back into the crankcase. How about hydrolic lifters that may be worn? It would help if I was more familiar with the engine but I am not.
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10-17-2012, 09:09 PM
Post: #5
RE: Big Diesel
Yep, quite a few internal oil lines. The mechanics have been checking all of the ones that they come in contact with. The relief valve in the filter housing is one of the ones that was pulled, checked & shimmed in my first post. They have been checking for galley plugs as they go. No hydraulic lifters. Tappets & push rods which are getting checked as it comes apart.

Even though you are not that familiar with this engine you are plenty helpful. I don't know what all the mechanics already checked & what they didn't. Each thing that you mention makes sure that we haven't forgotten anything. I'm still leaning to a cam bearing as you are the 4th person to mention that besides myself. But we won't know for sure until it's apart and that's no small job on one of these. Not like an auto that you run up on the rack and go to town. This is working outside and using a crane to lift the hood, air filter/turbo as a unit, the radiator & the fan before you can even start on the rocker boxes. That's why it may be a couple of days until I know more. That & the fact that I won't even be on the same job site tomorrow.

Thanks for the added information. I will pass it along to the lucky guys trying to fix this thing.

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Garner

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10-17-2012, 09:45 PM (This post was last modified: 10-17-2012 09:52 PM by Rupe.)
Post: #6
RE: Big Diesel
As you say, the theory is the same no matter where you are. As for experience, I have worked on big rigs such as fire trucks and oil trucks, and that covers rear ends well over 20,000 lbs per axle, 2 sp rears, transmissions, clutches, and even had a few engines apart on some Cat 3208s and DT 466 IH units. The fire trucks are the worst because the engine is generally mid-ship. You need a crane to pull the radiator through the top of the cab and if that's bad you might as well kiss the Alison trany good bye, or at least send it out for a new set of clutches. Electrical? Fire trucks are a maze of combination systems with 12 volt taps on a 24 volt system and sometimes using 120 volt AC on top of that with a dyna-mote (motor / generator) to operate certain specialty items.

Yeah, I have been around the block a few times.

Did I ever mention the 1928 GMC I did the engine on? I had to have the rod bearings "poured in place" and then machined to fit the crank. After had I had to hand fit each one using copper shim stock. They didn't use bearing inserts back then. Talk about old school stuff. Had lunch with the TRW rep. He found me a set of piston rings using a cross reference chart and measuring the old ones. It also had rope type front and rear seals, which I cut to fit from a Cady / Olds diesel. (the 350 V-8 version) There's a few other stories about where I found another trany and rear end for that antique truck but I will save it for another day.

BTW, that old truck was the first of the "full pressure lube" engines ever made. It had roller lifters and drillings in the top of the rod bearings to squirt oil at the bottom of the pistons. It was also the first of the overhead valve series with an optional oil filter via external pipes on the outside of the block. The return side of the filter fed another fitting on the back of the head to lube the rocker arms via a manifold bolted to the rocker stands. It basically worked like a garden sprinkler inside the valve cover. Looked kinda Rube Goldberg but worked well. That was 30 years ago and it's still running today.

Dumb suggestion... does it have the correct dip stick? IOW, if the stick is wrong then the oil level is not right! Someone should look up the oil capacity and match it to what the stick says to make sure it's not several quarts / gallons low (sucking air) or way high. (foaming) I have seen that more than once.
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10-18-2012, 06:06 AM
Post: #7
RE: Big Diesel
Very interesting stuff on the old engines!!!

The Dozer has had the same dip stick for over 20 years & we have been dumping 15 gallons of oil in on every oil change for over 20 years. I'm still leaning to something burnt up due to the loss in oil pressure since everything was fine until the 3rd time it lost pressure. But it still doesn't hurt to ask the questions "Just in case!"

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Garner

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10-18-2012, 08:32 PM
Post: #8
RE: Big Diesel
Well, the boss called this afternoon. I could hardly hear him but I could make out that he said that the cam was out & everything looked good. He was totally disgusted as he had hoped this would be the answer. He said that they are just going to pull the whole engine out and stick another in it since we need that tractor running. They will take the bad engine back to the garage & work on it in their "spare" time. That means that I won't know what the "fix" is for years. Sorry! Thanks again for all the input.

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Garner

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10-18-2012, 08:54 PM
Post: #9
RE: Big Diesel
I hate when that happens. You and I both know the guy who puts it back together will not be the same guy who took it apart.... and probably will not know the details of why it's even in the shop when the time comes. I mean, the machine is over 20 years old now so what's the chances it will survive long enough to need another engine?
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10-21-2012, 09:00 AM
Post: #10
RE: Big Diesel
Well, some "Good" news to report. On "Your" advice someone actually pulled the piston oilers before giving up and pulling the whole engine. The boss called me and said that one was bent and had a large crack in it that would have been dumping the oil out. They are going to replace it and try one more shot at running it. The big question that everyone is asking is, "What would have caused this?"

I told the boss that since you picked this as a possible cause you may also know why it would happen so I would ask you. So, any insight on that? I have been running this dozer for testing since I seem to be able to detect problems better than the other guys. It runs normal, sounds normal, power is good & no knocks or ticks. It just wouldn't hold oil pressure. The oil pan has been off several times and they didn't find any broken parts that I know of.

Thanks for using the forum,
Garner

Interested in Mining? Look here: Coal Mining, PA
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