sitting on the highway...

[shane96ranger]

That's true. If the crank is turning, the pistons are moving, and obviously the cam was not moving to open and close valves. There is probably more damage up top.


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[kunar]

The 2.9 and the 4.0 have a goofy timing gear setup, I've had one failure on each engine. The gear on the crank has a small nub cast into it on the back side of the gear. This nub fits into a locating key on the crank. The harmonic balancer pinches it all together to keep the stress off that nub. If the harmonic balancer bolt loosens, the nub will shear off and the cam quits spinning. Fortunately, these engines are noninterference, so no damage done. Put a new timing set in it and you're good to go. I know this is a quick/rough explaination, but it certainly sounds like what's happened in your case.

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[dispatchrobb]

Yes, nub on the gear is sheared off, and the locating key you mention on the crank, the edge on one side is broken off. So I assume I'm going to have to replace the crank?

 

[kunar]

Yes, nub on the gear is sheared off, and the locating key you mention on the crank, the edge on one side is broken off. So I assume I'm going to have to replace the crank?

replace the crank? i wouldn't think so. i guess i cant say without seeing it though. that nub and key-way don't really hold the gear from moving, they only index each other during assembly. the harmonic balancer bolt pinches the gear between the balancer and the shoulder on the crank. as long as that bolt is tight, there really isnt much stress on the nub. the problem is that if you dont get stuff together and bolted down tight with everything indexed just right, the cam timing can be off, which can really hurt engine performance.