I have a 1988 xjs V12, and not too long ago the belt connected to the smog pump broke on me, and the temperature gauge quickly rose. I pulled over immediately and replaced the belt in question, and have had no real problems with the car since then, several hundred (unavoidable) miles ago. HOWEVER, in the interest of caution, i'd like to make sure there aren't any faint symptoms that will lead to a larger problem. It's completely possible for me to leave it alone for now and ride my motorcycle to work, but it is so very cold these mornings! Any advice?

 

Welcome to the forum Shannonismard I've moved your post to the tech section where the experts will see it more easily.
Don't forget to post an intro in the new members section!

What makes you think you've dropped a seat?

 

Thanks for helping me move this, didn't see the XJS section at first. =]
Anyway, there's nothing that makes me think i may have one, other than the engine having overheated. Since I know nothing about valve seats other than why they fail, thought i may as well familiarize myself with what to expect if one or more do drop. This is my second jag, the first one(an XJ8) taught me that the key to owning these guys is an in-depth understanding of your vehicle. Am I right, or am I right?

 

If you had a dropped seat I think you'd know it. it would tick or tap loudly as the seat whacked up and down on the valve shaft as it opened and closed.

 

Hmmmm, see, there's the thing. There is a ticking, although not particularly loud, and it seems to only be present when idling.

 

Although my friend's super-mechanically-inclined mother immediately told me the ticking was a problem with the timing. Any thoughts?

 

I think your friend's super-mechanically-inclined mother doesn't understand why timing can't cause a ticking at idle.

It might be a fuel injector- nothing to worry about.

If you had dropped a valve seat insert, the engine would have refused to re-start or would run very roughly. You did well by shutting it off immediatly after the water pump belt broke.

 

Yeah, i thought that too, but she's given me enough solid advice in the past, it was worth mentioning. As far as running roughly, there is absolutely none of that, it's still so smooth. Definitely not a major problem then?

 

Jaguar V-12's will start run and idle in most cases with a dropped seat. It's a very unsettling clanking (and not very good for your engine in the least) but with 11 other cyls firing away it really doesn't care one isn't working properly. A lot of V-12 Jaguars are running around with an injector or two not working or a spark lead not firing and most don't even notice. it's not an odd firing engine like a Ferrari or Lamborghini 12 where it's noticeable but more like two side by side 6's....one of the big reasons you can't make it sound like a Ferrari 12. My friends E-type dropped a seat while idling right in front of us and while it started clanking away it never missed a beat at idle and started and drove right up on the trailer (while I don't recommend such action). It may be time to pull the cam covers and check the tolerances, does it get worse when heated or worse at fresh start idle or always the same?

 

It's really only audible at idle with the hood up. Other than that, even running hot, the engine is smooth and quiet.

 

It probably is just needing a little shimming on the valve train but I wouldn't be too worked up over it. I use a long screwdriver with the handle to my ear as a "stethoscope" and touch it on each injector to make sure they are each clicking and then use a reluctor pick up dwell meter to check each plug lead occasionally to make sure all twelve are firing. You could use the screwdriver method on top/along the can covers to pin point exactly where the problem lies (then again I hesitate to use the word "problem"). You can also get the manifold heat shields off and spray water on each outlet runner to see if one doesn't "steam" up indicating a firing problem. Otherwise I suggest you drive it like a rental, these engines like to be run!

 

Could it be the weights in the centrifugal advance? Mine was seized (who's wasn't???), and after I overhauled it there was an obvious clicking I could only hear with the bonnet up at low rpm's. That's because the plastic "thingy" was so brittle it broke while I was taking it out. Maybe yours broke on it's own.

See page 143 of Kirby.

Cheers,

John
1987 XJ-S V12
62,000 miles