Timing Belt Slipped 10 to 12 Teeth On the Camshaft? How?

Team D50

My D50 1986 2.0L auto timing belt has slipped 10 to 12 teeth on the camshaft from TDC on crank - oil pump was 1 tooth off - I have no reasonable explanation or evidence to explain how this happened.

Truck has 130k, put a new water pump and timing belt on 6k ago. Last week, started it up, drove 200', then it just died and would never fire again.

Removed the timing belt, the crank keyway has not broken, timing belt tension was excellent, no evidence of any parts getting caught under the timing belt which could allow it to slip. Next I'll remove the camshaft gear to check if the pin has broken.

Having no explanation for this problem would severely reduce my confidence in the reliability of this truck which I have owned for 15 years and would like to keep running....

Any ideas are appreciated.

-Fordman

Could be a valve that didn't open, thereby locking the valve train up. Could be a bent camshaft. Could be worn timing gears. Could be dry, locked, or bent distributor shaft. Could be simply a defective timing belt, or just out of spec. tooth spacing.

?? Further investigation is warranted.

rxinhed

Thank you for the ideas...................

Some additional info: in the past few months these are the issues with the truck when it was operational

1) consistent black soot deposits on the ground where the exhaust leaves the tail pipe
2) when starting the truck in the morning, camshaft squeal that lasts about 30 seconds
3) after driving, then stoping and turning off the truck, overflow tank would occasionally discharge a good amount of hot radiator fluid
4) using about 1/2 a tank of overflow rad fluid every 200 miles, oil level is always ok