So had an exhaust fire in RH exhaust Coil failure. REplaced coil, changed oil started back up sounded good. Ran for a few minutes then reved it up a bit............loud valve knock started after RPM's dropped. Was not doing before shutting off enging after exhaust fire. Remove all exhaust from down pipes back leaving only 1st Cat.........Any idea what might have failed all of a sudden......motor never registered any hotter than normal when the coil failed

 

Dropped valve seats, perhaps? That's a common cause of valvetrain noise on V12s.

I wonder if your exhaust fire transferred enough heat into the cylinder head to cause it?

Cheers
DD

 

Hey 92jaguarxjs - welcome to the forum. I have moved your post from the forum advice/feedback section to the XJS section where you will get better response.

Recommend visiting the new member section and introducing yourself when ypu have a moment

If you would - add a signature to your profile using the User CP link in the upper left include model and year so techs can provide accurate replies.

 

thought about that, but it runs very smooth except for the knock......would think a bad valve would be very noticeable

 

a bad valve would be noticeable if there werent 24 of them. you can unplug one cylinder and not even notice the difference while driving.

 

maybe so, but still hard to believe.....maybe a video with sound might help......maybe even wrist pin noise?????

 

Thanks for the reply last fall.........have been unsure of what to do next because as soon as I start tearing it down I can no longer let anyone else listen to the noise. I assume a compression check on the cylinder will show that I have a problem? I also read somewhere here that it is easier to remove and change the head by removing the engine????? Is that really true? I know there isn't much room to work on anything under that hood. I want to fix this baby and get her back on the road sooner the better.

 

If you are having to take the engine out then you could consider putting an exchange unit in; it would save a lot of money on strip down/repairs etc.