S3 V12 engine belts interchange numbers

Hi enthusiasts,

I have an '89 VDP that needs all engine belts. I feel my back hurting already.

As I am in Canada, and don’t have access to all the usuals for these parts. Are there common alternate belts made I can use?

I tried the old site’s parts interchange page, but they are not listed.

According to the JDHT site the belts are:

EAC1605 - A/C
EAC1323 Steering pump
C43070 cooling fan
EAC1616 or EAC 9369 Alternator.

We are having an early spring, and I’m itching to get this one out.


Hello Rob.

I’ve got several V12 new spares for long gone Es or XJs but some will have Unipart numbers or obsolete numbers I bet. Might be worth running a tape over them to match by length?

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Just take 'em to your local auto parts store for a match-up. They’ll have a belt measuring tool. Or perhaps the size numbers are still visible on the old belt. Many belt manufacturers use the same size identification language. For example, a 15335 marking would mean…
1 = v belt
5 = .375" belt width
335 = 33.5" length

(Or something like that. My memory is a bit foggy and I’m on my first cuppa coffee)

Yeah, it isn’t exactly a pleasure cruise.

Cleaning and oiling the threads on all the adjuster rods helps a lot


15/32" wide
33.5" long

While we’re on dimensions, I have a question about the effect of width on ‘length’.

The D-type had no jockey wheel or slotted bracket to tension the water pump belt. I instead the pump used a two-part vee belt pulley. The main casting bolted to the pump spindle had only a back flange. The central boss was threaded to accept the separate frontvee flange that screwed on and secured with a grub screw. The closer the flanges the bigger the effective diameter of the vee track and therefore the tighter the belt became.

My D has custom conventional pulleys and the belt is adjusted by moving the dynamo. However, with a tilted engine there is little room to move the dynamo in/out. I have a belt in place but it’s quite narrow and looks wrong with the modern notched circumference. Although narrow (3/8/"?) it sits clear of the base but I want a wider more old-school belt.

Clearly, the wider belt will sit higher in the vee and need to be longer. I could eventually calculate the circumference of the three larger diameter tracks on the existing deep pulley grooves but is there some kind of table or formula that can used to predict how much longer belts have to be for different belt widths on the same pulleys and shaft distances?

Length is at center line, so hard to measure without cutting it.

Never seen or heard of one. Maybe a local mathematician @soothsayer1 could tell us.
With all the belts we kept in stock, it was faster to just pick one.

Considering seemingly endless variety of belt dimensions, Peter; without knowing the specs given by the car/engine manufacturers - you have a selection problem…

The range of adjustment available gives you the leeway in selection. There are three belt characteristics; the length , the belt width and the ‘V’ angle of the pulleys.

Ideally; the belt should run level with the flanges of the pulleys - the thickness of the belt must be less than the depth of the ‘V’. The length of the belt could be measured by a tape wound over the respective pulleys - at max and minimum adjustment settings. The width is given by the span between the two flanges. The shape of the ‘V’ is a bit more circumspect, but must the same for all involved pulleys - with the belt angle to suit…

With these data you should be able to find something suitable…?

xj6 85 Sov Europe (UK/NZ)