I have 187,000 miles on my truck on the original timing chain and gears. I am the original owner and the truck has been babied since new. It runs perfect and shows no signs of any issues. Question is do the timing chains ever fail? If so, is it catastropic or not bad? I realize they stretch, but I've also heard that they often will outlast the rest of the engine before being stretched beyond their service limit. Opinions?

 

To check how much slop you have in your timing chain:

Pull the cap off of the distributor.

Turn the engine counter-clockwise, until you see the rotor move.

Mark that spot.

Turn the engine clockwise until you see the rotor move......

Mark that spot.

Determine the number of degrees of slop.

Over about 10? Time for a new one.

If you don't have a degree wheel, or marks on the harmonic dampener, to determine the number of degrees, take a string, wrap it around the dampener, transfer your marks to the string, and also, make a mark so you can determine the length of the string......

Measure length of string, (total)

Measure distance between "slop" marks.

Divide the second number, by the first.

Multiply by 360. This is the result, in degrees, of chain slop.

Quick and easy test.

 

I was in the same boat as you with my yellow 2nd gen (all well maintained, original owner miles). When I hit 160k miles, I decided to change out the water pump and timing chain/gears even though they had not failed me yet. The main reason I was changing them, though, was because I was replacing the plenum plate and already under the hood anyway... figured why not.

I did not measure any "play" in the chain, but it was surely much more loose than the new one I installed. Was it needed? Probably not. But, it gave me a good feeling to know I was probably good for another 150k or miles on those components. Plus, these water pumps are known to get loose and/or leak after some miles.

To me, its just good maintenance.

 

With that many miles there is no doubt the timing chain is sloppy.

 

If it runs too loose it could jump teeth?

 

It could jump a tooth or several teeth and possibly sheer off the plastic from the teeth and deposit them in the oil pan.
It won't do anything worse than cause valve to piston contact and bend pushrods, valves and possibly crack pistons unless it's turning high RPM and a piston came apart and the wrist pin gouges the cylinder wall.

Cheerful old bastard ain't I?

 

minus the cheerful, LOL!