I've got a 1996 4.0 Litre XJS where I'm trying to determine if the harmonic balancer is bad as it squeals a bit on start up and when accelerating - but not all the time. I pulled the air filter canister and put a chalk mark across the entire pully on the harmonic balancer. After driving about 150-200 miles I check the alignment on the chalk mark and it is really pretty close - maybe a 1/8" to 1/4" off all the way across. My question is if the balancer is bad, will there be a wild swing in alignment on the chalk mark across the pully(s) or is it fairly minimal? I'm wondering if I could have been that much off when I marked it?

The car has low miles (just turned 49k) and has been driven at least monthly for a continuous hour or so the 10 years I've owned it. I've had one mechanic indicate he thinks the squeal is the timing chain - it's been doing it for along time with no increase in frequency or degradation in performance. I did install the timing chain tensioner per the TSB a couple of years ago, but did not alleviate the problem.

Thanks in advance for any input.

 

Easiest way to check is to take chalk or white-out and draw a line from the core through the rubber and then the outer ring. Start the car and after you hear the squeal turn of the engine and see if the marks are still aligned. If not, the balancer is bad.

 

Timing chains do not squeal, rattle and clatter, yes.

I would reach down and tighten the belts the SMALLEST amount. Those threaded adjusters make it simple to do. That worked with the XJ40, and both X300's, same basic engine arrangement.

Age will have belts squeal, badly at times.

If that sorts it, or even changes it, replace the belts.

Your chalk marks being SO close to aligned has me doubting the pulley. The squeal from the delamination mostly has those mark waaaaay out after a few minutes. Your slight movement MAY be a sign of impending failure, but if it were me, I would clean it, and remark it AFTER the belts have been attended to.

 

Particularly the alternator belt.

 

Thanks everyone. I'll look at the belts but the AC compressor was replaced last year and I had them check the belts at that time (except compressor belt which was replaced) and I think I'll paint a thin line across the pulley's as I can keep checking it going forward.