Hi everyone,

I ordered a set of belts, including an NBD7740EA for the supercharger....which is the one I need according to belt suppliers....but it is four inches shorter than the one I just took off the car, which is a Roulunds Rofan 7K1185 and 47" long.

I googled around a bit and found this obscure page Carlos Gabaglio e Hijos which refers to the 7K1185 for this car...but where to buy one?

So my question is, what are you using on your car? Have you encountered a discrepancy in the length required vs what is listed?

Thank you,

The previous owner might have replaced both the upper and lower supercharger pulleys with larger ones to gain boost?

https://alleuro.com/Parts/Dayco/NBD7740EA

This site says that Dayco NBD7740EA is interchangeable with 7K1185 for use on the XJR6. But why yours off the car is 4 inches longer is very strange, growing by 10% after prolonged use?

Good point about (particularly) a larger lower pulley...I did consider that but am not convinced that's it because our pulley is steel, whereas the replacements I've seen are alloy...also our pulley just looks OE in size. I guess I'll have to get OE specs and measure mine.

Stretching is also a possibility, as this is an old, cracked belt. But there isn't 4" of take-up in the tensioner, or I'd fit the NBD7740EA that I ordered.

Thanks for your ideas.

Here's the new NBD7740EA inside the old 7K1185. Weird.

Rest assured your supercharger installation including drive pulleys is standard.
Cross referencing genuine parts to aftermarket parts is always a problem unfortunately with our Jaguars, especially a low volume model like the XJR.
After some research years ago I concluded that a belt in the range 7PK1180/1185 is the go and I have a 7PK1180 fitted to my car. Roulands was I believe the OEM supplier and in fact the belt fitted to your car is correct in sizing. Pinning down the exact factory size seemed difficult at the time.
I note that Dayco cross reference NBD7740EA to a size 7PK1095 (43"), the replacement belt you have, clearly not suitable, hence my above comments on part referencing.
My suggestion is to source a belt in the size range 7PK1180/1185.

John Herbert
(1996 XJR)

I am with John on this one.

After 55 years in Spare Parts, including Jaguar, what you have is NO surprise at all.

Even the Dayco listing is WRONG, as it lists 7PK1095 for that belt. I argued with them 2 years ago, just before retiring, as I was doing the belts etc on mine. They argued that their information is from OE sources, HAHA.

7PK1180 is also what I ended up with. Dayco = NO stock Australia, whoopee, Gates had ONE in Townsville, SOLD, to the grumpy South Aussie.

You are not alone, I also had issues with the S Type V6 belts, and even waaay back with the V12 beasts. Its Spare Parts, and we will never change them.

Thank you, gentlemen, I am encouraged by your assurances and grateful for you experiences. Now to find a 7PK1185 and not receive another NBD7740EA. Incidentally, 1185mm is 46.6", just what I have.
Edit: listen to me...referring to the XJR as my car.

Update: the parts guy at the local Jaguar dealer thinks I'm nuts. He only has NBD7740EA listed. I asked him what the mechanics would do when they received the wrong belt for a customer car....I did not receive a constructive reply.

I can't find a 7K1185 or 7PK1185 anywhere.

Plenty of 7PK1180 on Ebay and Google. Ebay and Google one of your best friends when you own a Jaguar.
Did not try 7PK1185.

John Herbert
(96 XJR)

http://www.kakapart.com/search/defaultsearch/7pk1185

Here’s your cross reference, not particularly accurate. A lot of belts are 100mm shorter.

There’s also gates 7pk1178 on ebay, $15 and ships from the states.

Just to close the loop on this...I ordered/paid for a Continental 7PK1175 from some dude in Latvia on June 18. It arrived today, presumably by some 19th-century mode of delivery. It was listed as a serpentine belt for certain Fiat models, but it works perfectly as an X306 supercharger belt.

Thanks for your help, everyone.

Is the issue not simply whether you can achieve the correct belt tension? Granted, the belt in the picture might be too short to go over the pulleys, but if it does, is it not simply a matter of belt tension?

Oh I tried to make it fit but there was not enough movement in the tensioner to allow it. That belt is four inches shorter, too much to make up for.

I should say, the 7PK1175 I installed is as short as you can go (being 1175 mm long). Mr Herbert's suggestion is bang-on.