Hey folks,

Been working on my 98 XJ8 replacing the timing chain with the guidance of a local mechanic. Long story short . . after replacing the timing chain and tensioners . . the car was driven for a short distance . .I would hear a *crunch* *crunch* and the car would shut off. So, I am here to ask you Jag experts . . if anyone can please share what the camshaft adjuster magnet does besides hold the chains in place and its specific functionality within. I am extremely curious to see if its faulty. Thanks in advance folks and happy thanksgiving to everyone. We all know Jaguar drivers need a break from working on it.

 

Here is a picture of the camshaft adjuster magnet; I've always thought it was the Timing Chain Sprocket.

 

That is a pic of the VVT Unit (variable valve timing). They are normally spring loaded to the 'retarded' position and when commanded by the ECM they advance the intake cam using oil pressure.

crunch, crunch is NOT GOOD.

bob gauff

 

Motorcarman,

Thanks for the reply. This part was such a concern because the timing chain was completely finished and then driven off. Then when accelerated. . .I heard that horrible noise and the car shut off. Do you happen to know how I could determine whether this part is functional or could be possibly faulty? Thanks again for your response.

 

So, did this occur just once and the engine has not been run since? Have you tried to get it to run since?

 

twice; it bent the valves each time and i've had to get the valves replaced. At first, I thought the timing wasn't correct. . but then I had the tools to lock the sprockets in place while I replaced the tensioners and chains. My question is now; how do I determine if the vvt unit/sprocket is faulty? I understand it is spring loaded and that brings up a huge red flag for me now. The engine is not able to run right now. Thanks for your input.

 

You need to lock the cams AND crankshaft for correct timing. Placing the crank at TDC and the cams with the flats horizontal IS NOT TIMED CORRECTLY!!!!!!!!!!!!!!!!!!!!!

The intake cam/VVT bolt is tightened with the cam pulled to the retarded position AND sprocket held tight by the exhaust sprocket and secondary chain, THEN the exhaust sprocket is tightened

The crank is at 45 degrees after #1 TDC with the locking tool installed in the torque converter drive plate at the correct oblong slot and the cams are timed accordingly.

If you keep repairing the heads and timing the chains incorrectly then you will keep damaging the valves. (definition of insanity??)

bob gauff

 

Thanks for the reply Motorcarman. Yeah, I understand what you are saying. My question is, is there any possibility the VVT unit can be faulty? If so, is there any way I can verify this? Thanks!

 

Not to be rude or unfriendly, but is this entire thread a spoof?

 

No spoof. just trying to found out the functionality of the VVT units from our jaguar experts on the forums.

Looks like the spoof is on you.

 

You can grab the intake cam with locking pliers or 'channel lock' type grips and rotate the cams to the advanced direction and they should attempt to spring back to the retarded position (easier to retard than advance). The rotation of the cams will pull them back with the engine running in the correct direction due to friction of the bearing caps and valve springs so even if the spring in the VVT failed they should NOT bend valves. If the VVT 10mm head socket bolts were not tight or the cam was in the advanced position when tightened, then the valves might contact the pistons when the intake cam advanced when commanded by the ECM. I have replaced at least a hundred tensioners and never had timing problems with the factory timing tools.

If the valves contacted a piston then you are missing a step in the procedure or have a serious mechanical fault.

bob gauff

 

Bob,

Thank you for the detailed response. That was the exact explanation I was looking for. I am going to test this out tomorrow at my mechanics and report back to you. Thank you again so much for all your help. I'll keep everyone posted.



(If you ever make it to the Bay Area, I'd love to buy you a round.)

 

X's2 with Motorcarman, if the VVT stick either advanced or retard it wont cause the valves to contact the pistons....only if something was done wrong will they contact

 

Chester:
Well, I guess the spoof might be on me-
I have never heard the VVT unit called the camshaft adjuster magnet, but apparently many online parts catalogs refer to it as that. I think that might be because a Mercedes or BMW has an electronic actuator which has magnetic coupling, and they copied the same name to the Jaguar's oil pressure controlled unit. Anyone know if that is correct, or am I missing something?
Then, I gotta say that putting an engine back together twice and bending the valves, I might think that I had something wrong in the timing. I would sure have a look at the manual after the first time, but I guess enough tenacity will overcome good judgement.
I am glad you were able to find the experts to help you out. Too bad it was after a bunch of extra work.

 

The other issue is to replace the upper tensioners you dont unbolt the intake vvt's, only the exhaust cam sprockets

 

Hey folks,

Back after a few days . . the machine shop just dropped off the block and newly replaced valves. I've just been contemplating what motocarman explained about the VVT units. It looks like it might be the timing correctly and might have to resort to a professional. I just called a local shop that has Jaguar experience and will see what the magic numbers might be. *waiting right now* Thanks for all your help folks . .will keep everyone updated.