Broken Marelli Timing Disc

I could use some feedback from the hive mind on my sudden loss of power issue. After driving for ~ 3 hours at ~ 60-80 mph my XJS lost power and left me stranded on the side of the freeway. While the engine would start, it has a terrible miss which seems to be ignition related. It will fire and run, but sounds like it is only running on 4 cylinders.

After spending 2-3 hours diagnosing the issue, I ruled out ignition coils, Fuel Injector issues, fuel pressure. I am 600 miles from home and have had to make arrangements to have my car flatbeded home. While on the trailer, I went to look at the front crankshaft sensor and found that 1 of the 3 “teeth” are missing. In other words, the one of the tabs which runs past the sensor is broken off. Fresh, clean, unr-usted metal is visible where the tooth should be. I believe this is the reason why the ignition system is not working correctly.
(I have to figure out how to post pictures to show the broken/missing tab/tooth FWIW. )

Has anybody here experienced this before?
My minimal internet search shows that this “Marelli Timing Disc” is no longer available. Any ideas where I can source one in the US?
I look forward to your comments.

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According to page 1D13 of my XJ-S Parts Catalogue your Timing Disc, Jaguar part number EAC9692, was damaged.
You will have to ask around Jag-Lovers, search eBay, or search the internet for someone parting out a Marelli ignition Jaguar for that part.
I wonder what happened to damage that part since this is not a normal failure.



ignition must be totally messed up by the missing tooth
as per Paul’s post, I wonder what could have broken this pat, as there is no effort on it, and it’s quite protected
are all the betls/pulleys still intact ?
any visible damage to the sensor ?

while you’ll be sorting this, I’d suggest you check to check the crank damper and get it rebuilt / replaced if needed, as it will be out to replace the ring

You can check vendors selling the said damper, as some may have the timing disc available, but didn’t think to offer it as it is not often asked for

edit : to post a picture, either copy / paste the link to the online image , or slide the image from you hard drive to the jaglover browser window : where you started a reply to your post (or edit the first one)

here’s the jaguar parts, the disc is item 21 , the crank damper is part 13

you may try

Jagbits website shows one timing disk , but the price sound a bit high @175US$

edit 2 :

check for new crank damper (sometimes called harmonic balancer) , as I’ve seen some include the timing disc you need

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I will be upfront, I have no idea how that part fractured. There was no one in front of me when it happened so road debris or stone really could not have hit it. The links to the photos are below. The fracture is fresh (rust free). It is always difficult to get good iphone photos in low light.
The fractured part…

One of the remaining tabs…

My sister asked how long will it take you to fix this. I said 6 weeks. :open_mouth:
There will be many “while I have access to this part, I will update it” moments.

Thanks for the feedback.

I honestly see no reason that can’t be fixed with a welder and some shaping.

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Well, I was able to get the Harmonic Balancer with the Timing tabs removed from the engine. It turns out that the harmonic balancer has failed.

Thanks to XJSV12COUPE for the links. It turns out the ebay link (Eurasia Parts) had the replacement balancer which included the timing disc.

Thanks for everbody’s input!


Thanks for posting back. It seems that harmonic balancer failures are not uncommon in the Marelli ignition cars for some reason. The one in our 1990 XJ-S convertible failed 10-15 years ago. The engine was making a terrible squealing sound on start up that eventually went away until the next start. Even though I knew the bond between the rubber and metal had failed, I could not move it like you did in your video. I removed and replaced the harmonic balancer myself and haven’t had an issue with the rebuilt one since.


yes the Marelli cars are equiped also with bigger alternators, and this add some load on the damper

@patbarbermi glad I could help
your damper seems to have been really shot : the movement could be a factor in the timing disk break

Your new damper pulley is a multiple micro V ?
this may be good news to me, as I’ve been looking for the replacement part for my car, and the 6.0L seem to have a different part number, as they do without the centering shims

this confirms baxtor’s experience shared on my thread about 6.0 harmonic damper

I sourced a 5.3 harmonic damper, but it’s an older one, so has a single V pulley.
getting the ebay part would give me a better option, provided I can get the missing shims (supposed to come with the 2nd hand part, they were missing, but are on my way)