I need to replace the broken alternator belt on my 1986 DD6 and am having trouble verifying the correct belt. I have a preference for Gates belts, but would consider recommendations on other brands. The OEM number I found for the DD6 is 3849 and have been advised that the belt for the same year XJS V12 would fit and that number is EAC1616. The old belt measures .410” wide and using a 1/4” wide tape measure I got 32-3/8” around the crank and alternator pulleys (not enough of the old belt left to measure length). I found these belts in a search for “1986 Jaguar XJ12 alternator belt number 3849”

ContiTech 3YHP66 Alternator Multi Rib Belt 3YHP66 for XJS XJ12 1986 1984 1987 1985 1973 1974 1975 | eBay

Dayco 15335 1978-1979, 1981-1988 Jaguar XJ12 Accessory Drive Belt - Dayco 15335 - Alternator - PartsGeek.com

Gates X-3759 Gates XL Alternator Accessory Drive Belt for 1973-1977 Jaguar XJ12 5.3L V12 ff | eBay

3849 Fan belt for Jaguar | 3849 | SC Parts Group 9.5 x 850 mm (.374” x 33.46” )- Lucas alternator
Most of the listings do not have the dimensions, and some appear to not be correct. Does anyone have the correct Gates belt number, and do you recommend the cogs on the underside or on the back (Dayco brand?).

 

It looks like everything with the 75 Amp alternator takes the same belt, from E Type to XJ and XJS. The belt length for EAC1616 is specified as 850mm.

Gates 7335 should be the right one. I see the Dayco 15335DR on closeout at Rockauto for under $2 now. It cross references to the correct part number.

 

Thanks for that information. I did check RockAuto and their shipping cost made the $2 Dayco about the same as the Gates 7335 from V belt Guys ($13.20 total) so I ordered the Gates. It is a little longer than the OEM at 865 mm to 872 mm (depending on whose web site you check), so I hope there is enough adjustment. My DD6 has just 65,000 miles on it so I suspect my alternator belt was the original one.

BTW, am I correct in thinking a cogged belt (notched belt?) is used for smaller pulleys and a solid belt for larger pulleys? I think the alternator belt is the only one with cogs on my Daimler. Oops! I take it back. All the belts have cogs.

 

11A0850 is on all my V12's, even the HE with the Bosch 110Amp alt, fitted by me, not the factory.

Internal cogged became a "thing" in the late 70's withe the shorter belts, and smaller pullies. Claimed to stop slipping, cracking, etc. Dunno,

Then the "Top Cog" became the flavour of the day, CLAIMING it kept the belt cooler,and we were all sucked it.

5 years in a V12 engine bay, you be blessed.