Timing chain guide necessary?
 

Just finished replacing the timing set on my 99 XJ, got home from the DIY shop and realized that I forgot to slide the new timing chain guide in the timing cover. How critical is this piece? I figured I could get away without it for a while as long as the chain isn't loose enough to slap up against the cover. Since the chain is brand new that shouldn't happen for some time.

Thoughts? Do I need to take it all apart again just for this part?

I did the same thing. I ended up taking it all back apart and putting the damper in. On the plus side, it was a lot quicker the second time. IT seems like you could run without it and if you start hearing it slapping against the timing case then you take it back apart. Seems like you'd need a lot of wear in the chain to have it start hitting the metal.
On the other hand, if it starts hitting the metal timing case, I have to think it would wear it pretty quick. But the damper is essentially hardened plastic that wouldn't stand up to a chain for very long.
Did you hear nay metal on metal noises when you drove it home?

Take it apart, put it back together correctly, or wish you had.

Sounds great so far, nothing funny. So I guess the main thing I'm looking to find out is how long on average does a timing chain take to gain enough slack for the damper to be necessary.

I don't know if my old one was original, but even with how loose it was(it was pretty loose), it wasn't hitting the damper yet. If it was the original, then I should be good without a damper for at least 215k miles. For a DD and occasional off-road I would think the timing chain stays tight for a while.

Got any specific experience with this or are you just saying that?

I would probably just take it apart again without question if I didn't have to pay a DIY shop to work. But I would really like to know the life of a timing chain to help make a decision given my options.

i doubt many non ohc motors see that piece as being essential. sbc hadn't used them for decades.

Take it apart put it back in and forget it ever happened. We wont tell.

It's got nothing to do with the life of the timing chain.

It's got nothing to do with the life of the timing chain.