1981 300SD Timing Chain Disaster

[Topspin]

When my son was driving from Tucson to Phoenix last weekend, he heard a loud clunk followed by a quick rise in engine temperature and unusual noises. He immediately pulled over and turned off the ignition. When the engine did not shut down, he raised the hood and used the manual shut off.

Attached is a photo of what he saw. The vehicle was towed to a repair shop. After removing the valve cover, they discovered the following:

1. The upper timing chain nylon guide rail was broken and parts of it had apparently lodged under the chain and bent the guide rail attach bolt.
2. The chain had skipped three links although there is no apparent damage to the camshaft or supports.
3. The exhaust valves each measured .018 (loose) but the intake valves indicated normal clearance.
4. The car did not "boil over" and there was plenty of oil showing on the dipstick.

The timing chain did not break. What caused the chain to break through the valve cover is still a mystery, although the timing chain tensioner is suspect. The timing chain and tensioner were replaced about 3 years ago.

If anyone has seen this happen before on a diesel and has clues as to the cause, your input will be appreciated. The car has @240K miles, uses no oil, and is well maintained.

Thanks in advance for your help!

Larry Campbell
1981 300SD (240K)
1979 300SD (325K)
1982 Chevy 1/2 ton P/U 6.2L diesel (202K)