tina.c93

Hi guys - I know this is probably a really dumb question, but could you tell me if my 1993 cherokee xj limited (4.0L I6) has a timing belt or a timing chain?.. Im getting mixed answers from friends and from google. If its a chain, how often should it be replaced?. Ive just bought the jeep, and it doesnt seem to have been serviced for a long, long while (there was actually moss growing out of the air filter!).. Im getting the old truck back on its feet, learning as I go.. any info would be greatly appreciated

mike albo

its a chain,depends on how many miles and how it was serviced

89Laredo

Chain.

5-90

Chain.

I've seen timing chains actually go - in some limited instances - a million miles or so! Typical life seems to be 300-500Kmiles on average, with 600-700Kmiles being something that can be expected (sorta) from the OEM "silent link" laminated chain.

NB: All AMC engines used timing chains, and most American OHV engines use timing chains. You'll likely find a belt on an OHC engine, but that's not a hard-and-fast rule (I was pleased to discover that the car my wife wanted was a DOHC inline six, driven by a single-roller chain. Still can't get used to it being jammed in crosswise, tho...)

The typical failure for a timing chain is stretching - which starts to throw cam phasing off after a while (since the distributor is driven by the camshaft, ignition timing goes to Hell as well.) Test thusly:

IF YOU HAVE A STROBE TIMING LIGHT:
- Check ignition timing at the harmonic damper (you may need to fill the timing notch on the damper to make it more visible - I like to use gloss white fingernail polish for this. Daub it in, and wipe it off of the surface - the mark should stay filled.) If the timing is steady, you're fine. Excess stretch in the chain will manifest as "wandering timing" at idle - and it will wander more than a degree or two each way (a little bit is normal in a computer-controlled vehicle. It's not set mechanically, it's set electronically and it's adaptive.)

IF YOU DO NOT HAVE A STROBE TIMING LIGHT:
1) Remove the distributor cap.
2) Using a 3/4" socket on a breaker bar, turn the crankshaft clockwise a few degrees (15-20 should do - you're taking slack out of the chain.)
3) Make a mark at one edge or the other of the distributor rotor. Make a mark on the harmonic damper at or near the "zero" timing mark.
4) Slowly turn the crankshaft in the opposite direction until you see the rotor just start to move!
5) Check the mark you made against the timing scale on the front cover - it shouldn't have moved more than a couple of degrees. 0-2 degrees - you're good. 2-5 degrees - plan on a timing job soon. 5+ degrees - timing job now.

NB: You can also turn the crank, using the OEM timing mark, past zero clockwise and turn it anticlockwise to take out slack. Then, go clockwise and use the timing marks. The basic idea is to take the slack out of the chain in one direction, and then see how much there is in the other. You're indirectly measuring the stretch in the chain - but you're doing it using the more important measurement anyhow (chain deflection is unreliable, and require exposure of the chain. Isn't this much easier?)

NB: I've got somewhere well north of 300K on the clock on my 88 (gotta fix the odometer...) and it's just gotten to having one degree of deflection using the mechanical test (second test above.) I'm probably good for another 300K - or whenever I finally build that stroker and put it in.

tina.c93

Thanks guys.. knew I could rely on you!. Thanx especially 5-90.. your answer was great. Ive copied and pasted all that info for later use!. Im sitting at 155k, so hopefully the chain will be good for a little while yet.. something I can tick off my "Do Immediately" list.. I have a Haines service and repair manual enroute.. god knows I need it!