big troubles with a big cam

There's an old saying that the only thing harder on a vehicle than running it all the time, is not running it all the time. In aviation, we used to say that if you didn't fly the plane daily, the electrons and fluids forgot what they were supposed to do. And in the case of vehicles used spradically on a farm, this comes to pass. The truck sits for 9-10 months a year with not much activity, and then it warms up and runs for a short period, and then goes back into a static mode. The odds are that you need to bite the bullet here and go completely through the motor and rebuild it. Things just go bad and corrode from sitting, and I would suspect that this is the root of your problem. I worked on a farm where we drove the trucks daily in commercial haulage, and we seemed to have less problems than the guys who only used their trucks at harvest.

The upside of this is that the Cummins Big Cam 400 is one of the most inexpensive motors to rebuild and there are plenty of parts around. You say it has had the valves done, so you can probably put in sleeves, pistons and bearings and be in pretty good shape, as long as you keep a close eye for signs of any other potential problems. If you have the shop space, this would make a not too bad summer project, and you would be ready to go when the corn turns brown.

I have some possible doubts about your mechanic, but I am only hearing part of the story. As a mech, if the truck neded one sleeve, it probably needed 6 of them, and not doing them all while the engine was already torn down seems a questionable decision to me. I can't tell from here if it was his fault for not telling you what needed to be done, or if he had the impression that you were really financially strained on this. But, I don't think I would ever just replace one cylinder if I were doing it. That strikes me as just patching things up rather than fixing them properly, and goes against my mechanical beliefs.

 

the only real solution is a complete teardown....

it will cost you $500000000000 to fix it one piece at a time...

Do it all at once and save $$$.


Drive it every week too regardless of necessity, as like the other guy said, if it is always sitting it will have problems that it would not get if it was rolling atleast a little.

K

 

it'sextremely hard to diagnose an engine from behind a keyboard, so the best any of us can do is general advice. Without actually seeing the engine and putting hands on it, remote diagnosis is a tough gig. We have a few clues, and they are possible leakage of the oil cooler into the cooling system, or a head gasket leaking. We also have coolant getting into the oil, so it i possible that there are multiple problems with the engine, many related to wear and time. You could have pinholes in the sleeves losing fluid into the lower end. Pinholes can form from vibrations within the engine combined with the air bubbles in the cooling system and work their way through the sleeves. Unfortunately, about the ony test you can do to the truck is to have the cooling system pressure tested, and that probably won't provide all the answers, though it might give some clues that could point you in the right direction.

I don;t have any idea how mechanical you are, so i can;t say whether or not you should take the engine down yourself or have the mech do it. If the mech suggested at the time of the one cylinder replacement to replace them all, the it looks like he is up to snuff and knows what he should do. Unfortunately, you are in the position of putting money into a relitively ancient truck, so it is not a simple dollars and cnts issue. You have to decide the emotional value you have on the truck and balance that against the cost of rebuilding the engine. Luckily, you have a relatively low cost engine to rebuild, parta are cheap, and knowledge of the engine is fairly common.

But you have to make the call whether it's worth it to rebuild what you have, replace the engine, or cut your losses and replace the truck. Personally, what I would probably do is talk to the mechanic and make a deal with him. Take the engine apart yourself, and get a look at what condition it is in internally. If the source of the problem can be found and you can fix it reasonably, then buy the parts and have the mechanic rebuild it for you. You save his costs of tearing it down, and he makes the money from putting it back together. The parts cost is the same either way. If you can't fix it reasonably, then it is worth about the same without the engine that it is now with a faulty one.

Cost wise, a rebuild on a Cummins without any machine work should come in under the 2500 mark, and add in the cost of the labor. You may come in below that since you probably don't need to buy cylinder heads if they were redone recently. Swing by your local truckstop and you should be able to find some truck trader papers and they will have sources for the parts, and if not then people here can point you to some places that carry what you need.

That;s the best advice i can come up with for your situation, based on what we know about the engine. Hope it helps.

 

One other thing you can do that will help as a temporary measure. Drain the oil down and replace it, which you need to do anyhow since it's contaminated. While you have the drain plug out, drill the plug through and tap it for a small 1/4" drain line with a valve on it. That way, if the engine has been sitting for a while, you can drain off any accumulated coolant that has settled to the bottom of the pan. If it sits for a while, the coolant will separate and be at the bottom of the pan, since oil is lighter in specific gravity than water or coolant. I once kept an old 903 Cummins alive for about 3 years of leakage using that trick. Eventually, it did spin a bearing on one of the mains and it wiped out the block, but then we went ahead and rebuilt it from scratch using a spare block we had.

 

you should also look into aftermarket head gaskets. when cummins changed the head gaskets a few years back, they have been having trouble with them since. I've found that aftermarket head gaskets with .020" over coolant grommets make it all much better.