Sunday, May 19, 2013

A DT466E engine failure with progressive damage

Hello, everyone.
Today I wanted to post a short note about engine problems and progressive damage. I recently finished an inframe rebuild on a DT466 that suffered classic progressive damage. What happens is that a major component will fail but as the truck still runs, the customer will keep driving, causing additional damage until the engine finally quits running.
When the truck came in to the shop, the engine would not run. I was told that there was coolant in the oil pan and that another shop had looked at it and decided not to tackle the problem. I proceeded as if a standard inframe was needed, but as soon as I removed the valve cover, I knew I was in for more. An engine with a badly overheated component that fails catastrophically has a distinctive odor, and that is what I smelled inside of this one.
The first indication of a serious problem was seeing that the #3 exhaust pushrod was bent into a pretzel and the cam follower guide for that cylinder was broken. This problem is not uncommon in the 466, and it meant that the cam would need to be replaced, adding about 12 hours to the inframe job. When the head was off I expected to see some damage, but the #3 piston crown was completely melted and a large piece of it had been banging around in the cylinder. At this point I realized the truck had been driven for a while after the problem started, and I was prepared to see more damage as I continued disassembly. I was not prepared for what I saw next. That #3 piston was seized in its liner was not a surprise, but seeing the extent of damage to that liner was. It was split lengthwise in two places and had to be cut off the piston in order to remove the rod. A picture of what was left of the piston is shown below.

Damage suffered by DT466E piston, compared to the (relatively) undamaged one.

The failed piston had spit metal into all the other intake ports, so many of the valves were leaking; stoddard solvent ran out the valves almost as fast as it could be poured into the port, and #3 exhaust valve was bent. I also found that the turbo impeller had seized tight, but luckily had not made contact with the housing.
So, my idea of what happened was that the #3 cam follower guide failed, letting the follower turn and soon damaging the cam lobe(s). Of course, this caused a dead miss, but the driver or his company decided to finish his delivery route. Soon the valves in that cylinder wouldn't open properly, and the piston started to overheat. The liner may have overheated to the point where the o rings failed, or maybe the piston expanded to the point where it split the liner. Whatever happened, coolant poured into the oil pan and damage progressed quickly. The turbo didn't last long running its bearing in coolant instead of oil, and it failed, drastically reducing power. My guess is that this is when the truck was finally stopped, or maybe the driver just got tired of all the hammering the engine made and the low coolant and overheat alarm going off.  Or maybe the smoke cloud following the truck tipped him off to a serious problem.
I have replaced several failed cams in the 466 engine, and most drove to the shop. All that is usually required is a cam change, a couple of followers, and pushtubes. Although not an inexpensive repair, it is much better than risking the type of damage seen in this case. I have never seen this kind of progressive damage after a cam failure, so the vehicle must have been driven quite a while after the problem was realized. I understand the desire to finish a delivery route with an unexpected engine problem, but at some point I would think one would have realized this problem was more than a failed injector or another fairly minor problem.

A list of parts needed illustrates the extent of damage the engine suffered:
Inframe kit: liners, pistons, rings, and bearings, and gaskets
Camshaft, 2 cam followers, and 2 pushtubes
Injector for #3 cylinder
Intake and exhaust valves for #3 cylinder, plus machine shop work to regrind the valve seats

In addition, all valves had to be removed, the seats cleaned and relapped, the intake manifold and inlet side air-to-air tube had to be cleaned.

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