Changing drive belts on 1988 XJ40

Any help would be welcome

Alan, are you looking for general tips or are you looking for help with (a) specific belt(s)? Your '88 is no doubt different from my '94 but hopefully someone with an '88 or '89 will chime in.

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Hi Mike.

Mine is the MY1988 with two ribbed (not toothed) Belts and no tensioner wheel as far as I can see. I have removed the shroud and the fan and have good access to the alternator side. I am hoping that I can get to the other side from underneath. It looks too crowded on top!

Further, I have successfully removed the fan and shroud, which must come off together. This gives me good access to the water pump/alternator belt. The belt that worried me was the aircon belt which must come off first and go on last. However, I have not used the aircon for 20 years and so I opted to cut the old one off to give access to the other belt and not replace the aircon belt. As a matter of interest can the aircon belt be done from beneath – in case I ever opt to do it?

Yes, that is how you do the A/C compressor belt, from under the car. At least you don’t have a damn air pump belt to deal with on your 88.

No idler pulley on an XJ40 BTW.

Did the job but new alternator belt is squealing when I first start off. Too tight or too loose or some other reason? If either of the first two, what method of gauging the tightness is recommended.

too loose, tighten it up, I just do it by feel but I’m sure there are better ways!

Hello Alan - checking the manual, if using your thumb (in other words you do not have a belt tension test tool), find the longest belt span, for the section you are working on (eg. alternator); a span is measured at the tangents of the pulleys where the belt is still seated; if in a span of 7 to 10 inches, you want approx. 1/4 inch deflection; if in a span of 12 to 16 inches, you want approx. 1/2 inch deflection; the deflection is from a straight line, at the outside of the belt, with the belt at rest, then pushed in towards the inside of the belt; the deflection point is at the midway point, on the belt, between the pulleys; if you put a straight edge guide (ruler or piece of wood) along the belt, reaching from pulley to pulley, at a point where the belt is seated fully, then you can see the distance you are pushing the belt away from the straight edge item - Tex Terry II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - 3/26/2020 0006hrs. EST USA.

Yes. On my 89,loosen bolts back off tensioner screw reverse for new belt.

Very familiar with that part. For others, the difficulty with reaching the lower nut with the spanner is solved by liberally applying WD40 so that both nuts can be shifted easily with the fingers once untightened. Untighten upper nut whether the tension is to be lessened or not (easier to reach), lever the alternator with a suitable object and then tighten lower nut with fingers and finally upper nut with spanner.I t was the amount of tension that was the issue. Larry’s post clarifies that.

Alan, the last time I replaced the alternator belt (it’s a V-belt) on my '94 I had to re-adjust it two or three times before it finally settled in. Not wanting to over-tighten it, which is bad for the alternator bearings, I tightened it just enough to eliminate the squeal. After a week or so of operation I would get thd squeal at startup. Tighten just enough to eliminatd the squeal, drive a while, adjust again when squealing at startup returned. Ultimately eliminated the squeal,but it seemed as though the belt was tighter than I would have thought appropriate based on the traditional deflection test.

Thanks. I have fixed it and developed a tool to help. Posted in another thread.

I once had a squealing belt on start up and when RPM got over about 3000. Belt tension was OK but found the fan clutch had seized and this extra drag at higher RPMs or on first start up caused the squeal. (1990 XJ6)

You have to be careful with the 40 now that they are getting old. A “belt squeal” on startup is usually a harmonic balancer that has de-laminated. Check your belts to be sure they are properly tensioned (1/8" deflection) if they are then your harmonic balancer must be repaired/replaced. Dale Mfg. in Oregon does an excellent job with the rebuild. DO NOT use a used non-rebuilt balancer. Removing the balancer itself is not difficult. You need a 1-5/16 inch six point socket for removing the balancer bolt, NAPA carries just what you need for about $15.00 USD, a proper puller with 8mm X 1.25 screws. You can get the proper Jag tool kit for the job for a little more than $100.00 USD. There is plenty of info available on removal and reassembly.
Good luck!

Hey Roger I beg to differ on the screws (you quoted 8mm X 1.25) and while these CAN thread into the balancer with some effort, they will destroy the threads in the cast iron in the process - the correct size is not metric, but SAE 5/16"-18 …BTDT.

Maybe, that’s what I used? I had no trouble with any aspect of the job and everything was trouble free!