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Discussion Starter #1
What is the likelihood that my original 4.2L with 189k milesjumped a tooth on the timing chain? I’ve read ALL the history of this engine,which mainly speaks of the dropped cyl liners, leaking head gaskets and camwear, but I can’t recall reading about timing chain jumping.
Truck has been purring like a kitten, no oil usage, no leakinghead gaskets, but at a stop light the engine just died quickly. I changed outthe ignition module because I’ve had ALL THOSE troubles before, and I installeda new fuel pump a year ago, still no fire. Engine spins over freely, but nofire.
I had it towed to a shop and he said he can’t get to it fora while, but mentioned the timing chain possibility.
Has this happened to anyone? Would it happen a idle? Wouldn't there be a mechanical noise?

 

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I would think that's a pretty unlikely scenario. Even at 189K, the chain would have to have a LOT of slack to jump a tooth, and it would likely jump more than one if it did. Then the engine would be making all sorts of horrible noises when you tried to start it as the pistons would be hitting the valves.
You can pull the distributor and stick a long screw driver down in the chain case to see how much slack is in the chain. A compression test would also tell you if the chain had slipped because the valves would be open during compression.
I would start with the basics (air, fuel, spark) and go from there.
 

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Discussion Starter #4
Thanks, that makes me feel a little better. I rebuilt the dizzy about a year ago, so I can't imagine it's a cap/rotor thing, but I guess nothing will surprise me now. Just bracing myself for what the shop tells me.
 

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The shop is going to tell you you need a new timeing chain
And it probably does
And if you get a year out of a cap and rotor
Your ahead
 

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They will run with it one tooth out, I've seen one like this but not from jumping just installed wrong and wouldn't rev.

Also had a failed cam wheel, plastic tooth wheel section detached from inner cast spokes, aluminium? It was on an engine which I got going for someone with it on a bare chassis, advised owner to change cam chain etc while access was good prior to install into a series 3. This was ignored and failed about a year later. I advised it based on stories I'd heard about failed cam wheels and engine had no provenance to judge it. Seemed logical to me to sort it while it would have been about an hour labour.

You'd see this with no rotation on distributor shaft when cranking though, so worth a check.

Bent pushrods but no bent valves, surprisingly. I saw it but it wasn't me fixing it so just observation and it did run ok afterwards. I was really sceptical that no valves where damaged.

I use cap and rotor for much longer, currently about 8 years on this set.
 

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I dealt with something similar a while back. I had rough-idling issues after an engine rebuild, which was traced back to a poor wire connection with the Ignition Amplifier Module, an old distributor rotor, and having to reset the base idle. In order to run smoothly, the engine timing, base idle, and resting throttle position have to be at equilibrium; I've found that a lot of engine idling issues can be traced to this or the distributor (which sounds like it should be fine on yours).

FWIW I replaced the timing chain on my engine during the rebuild. At 174,000 miles the original chain had stretched A LOT; I imagine it's the same for yours at this point. I'd recommend replacing it the next time you replace the water pump. New chain below, easy to replace once you get to it.

280678
 
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