Now I know that most of you out of the book Jag mechanics will not approve of this change and it was not my idea but it really makes sense and works. I am not a Jag expert as many on this forum are and I am happy for there input,but after reading all the posts on tensioner change and the tools needed as well as the cost, I was thinking that most back yard mechanics would not want to make a dive into what is really a very easy job. Tools needed was a 1/4 inch and 3/8 inch socket set,inch pound torque wrench and two plastic tie wraps about 8 inches.Removing the valve covers as with any job replace as it came off, do not know why but replace coils as they came off, clean out plug holes before removing plugs(I used a air hose)mark the top side of each cam bearing cap (I used white out) with a socket and wrench turn engine over counter clock wise looking from the front until all lobes are off the the valves.Then run the plastic tie wraps through the exhaust cam (lower)sprocket and around the chain tightly.Remove the cam bearing blocks and lay in order(must go back same as removed)With help from a friend lift out the cam enough to tilt forward and remove old tensioner and install new one, finger down all bolts then torque to 7 foot pounds, install valve cover,plugs coils,and cover.Now after really thinking about timing,you stand more of a chance of changing the timing by removing the sprocket from the cam then doing it this way.As I said I am not a Jag mechanic and if they were working on my car I want them to do it by the book, but in my garage any thing goes.Thanks
Bill
1998 XJ8 VDP

 

Hi Bill

This "tie grip" method has been discussed a few times on this and other forums. I used this method to change mine and it went flawlessly. I think there is usually some inputs on this from the various (excellent) Jag Techs that frequent this board, and I think what you said in your post resonates with their feedback, ie if they are doing it on a customer car they should (and do) use the correct procedure, because after the car is driven out of their shop they may never see it again, so they have to make sure it's done right.

Wheras you and me probably spent the next 1 week after we did it listening intently every time you started the car, and drove it carefully for a while, etc, etc, and were aware of the risks. I also had similar thoughts as you about how you could potentially impact the timing, and as the timing chains never come off the sprockets, and the sprockets don't come off the cams using the tie grip method, I also can't see how you could impact the timing. Admittedly I have a supercharged XJR which doesn't have the variable valve timing like the normally aspirated cars, so I'm not sure if there is more risk there.....

 

worked for me to,although I dont remember removing the bearing blocks completly,just loosened them enough to raise the cam

 

In my journey into changing tensioners, and then leading into changing all the chains & guides, I used that method once. The Jag dealer lent me a new tensioner with the thought that the one I purchased from them might have been defective, since I still had chain noise after changing the upper tensioners. The parts man called me as they were doing inventory & needed it back. I did not have the tools that day, so resorted to that method. When I did it, I rolled the engine to the normal lock down point and laid a 6" ruler across the cam flats. That way I could be sure the cams were still in the same position after assembly.

One drawback is the inability to pre-tension the chain. If there is anyslack on the drive side, it can lead to rough idle as the timing can be out slightly.

 

But when bolted back up, and once the tensioners fill with oil, doesn't the chain retain the same tension it would have had previously? The sprockets have not been moved relative to the cam OR the chain so neither tension nor timing has changed at all; except for any chain stretch, which existed just the same, prior to replacing the tensioners, IMO.

If this is the case, then you're suggesting that by removing and replacing the sprockets, you are able to pre-tension, effectively taking out any effects of chain stretch, correct?

 

I am not the final authority on this, and I agree this method does work, but you are putting in new tensioners which have slightly less stroke length (according to Jaguar).
Technically I think you are correct that with the zip ties on the sprocket and carefully aligning the cam when putting it back in you should be close, but it only takes a slight difference to introduce slack on the drive side.The camshaft is free to move back slightly, and in theory, you would need the same pre-tension to have it identical.
Without access to the tools, I would... and have used this method, but the job is certainly easier with the tools.

I also agree that a slight amount of stretch may be corrected with the tool, but in my case the only solution was new chains.

I am not making a strong case against the method, just adding a bit of background.

 

I guess you can do this, its totally shade tree, and yes it does not allow to readjust tension from chain slack, sprocket wear and difference in specs between old and new tensioner to get ALL the slack on the correct side. It can only keep it where it started. that why the sprocket is a slip fit and not keyed or splined, so on reassembly you can comphensate for it. I still say do it the right way, the tools are out there shipped from person to person. With the tool i can do the job faster and more accuratly than the formentioned

 

I think you all make great points and what ever works for you and does the job then do it. Always enjoy reading your feed back. As I said I am not a Jag master tech, but I am 71 years old retired 3 times 40 years electrical mechanical engineer and product designer with 21 patents, so that might account for something. I am now working part time as a John Deere tech.Thanks for the input.
Bill
1998 XJ8 VDP

 

retired 3 times, couldn't get it right the first 2????
Sorry Bill couldnt resist. my sister in law in Iowa used to be a field engineer for John Deere in the 80's and 90's (she grew up on a farm and the town didnt even have 1 traffic light....
The statement from farmers on their equipment was "I thought they were sending an engineer to look at my combine?" to which she always replied
"they did, youre lookin at her!"
Bill

 

Bill
Not many females in the field,great come back.
Bill

 

Ya.... What he said!

I would only go without the tools in an emergency situation, as was the case the one time I did it. I got may hands on the tools again when doing the complete chain job. And it is easier with them.

I drove past the John Deere factory once in my youth on a Norton 750 going from Calgary to Greensborough. I thought I noticed a very fine looking engineer!

 

Can I ask what tool set you are referring to? I have searched and come up with no reference # or brand or place to purchase? Thank you and sorry for my ignorance, just bought a '98 XJ8 and I love the car, just had the uppers done at a local shop and they said that I needed to do and upgrade the lowers, as well as chains, guides, etc. Is there a reference parts list that I can refer to and a recomended place to purchase these items? Thank you to everyone here! I am going to tackle this myself asap and this forum was what made me convinced I could do it myself. =)

 

The main tools you need are to lock the cams down and hold them, and you have to use the sprocket tensioner when tensioning the chains. I brought this methos up when i just went back to engine school on the new 5.0 and refresher on the v6 and v8's. We did it with tie straps and even using the correct jaguar tools excpt the sprocket tensioner and every time it left too much slack on the wrong side of the chain when not using the sprocket tensioner. This causes the engine to be slightly out of correct cam timing

 

Always had a concern about the zip tie method as 1-2-3 degrees if very hard to judge by eye alone. Thank you for an authoritative answer to this long standing issue. Did mine with the correct tools hopefully correctly.

 

I still don't see why the zip tie method doesn't just leave it with whatever valve timing you had before, no worse and no better.

 

It does, and it must... If you do the 'correct' method, it does remove the small angular change due to stretch, but ONLY between the upper two sprockets, not between the intake sprocket and the crank - which is MUCH more (due to the longer chain path) than the difference up top. So the 'correct' method times the two cams together properly, overcoming stretch up top; but, since only the exhaust sprocket is adjusted, overall cam timing is still off relative to the crank because of stretch.

Upon completion of the 'tie wrap' method, the two sprockets and the VVT system will be aligned to each other EXACTLY as they were before the operation... just not, perhaps, as they were when new, because of that chain stretch. This mis-alignment is so small as to not make me worry one little bit. If it takes jumping a tooth to make it idle poorly, then the angular change due to stretch is going to be some TINY fraction of a tooth, and therefore, un-noticeable IMO.

Bottom line - this method maintains alignment between cams and crankshaft EXACTLY as it was just prior to replacing the tensioner. If the engine was running well, i.e., if the chain hasn't jumped prior to beginning this task, it will still be in the right place after. If, however, the chain has stretched enough to cause poor running issues then the chain, lower and upper tensioners all need to be replaced, making arguments over how to properly change ONLY the upper tensioners moot.

 

I think the issue is that the new (3rd gen metal) tensioners have different dimensions than the old (plastic) ones.

 

This does NOT affect the chain length between the sprockets - the tensioner pushes on the other side (slack side) of chain, so distance between the cam and input sprocket, and the input sprocket and exhaust sprocket does not change (except for stretch) as they are always under tension from the crankshaft sprocket.

 

It does.

As for the concern about "1-2-3" degrees goes, there is no "1-2-3" degree adjustment without loosening the cam bolt. It is much coarser than that.

If the cam sprocket has, for example, 30 teeth, it is going to be either dead on, or a multiple of (360/30)=12 degrees off. This presumes that all other things remain stationary. The error of course will change depending upon the real tooth count. There are photographs around for the curious.

In the zip tie method, "dead on" is defined as "same as before, no better, no worse". That is not a bad thing. The factory robots probably did a better job at the original alignment than anyone can replicate in the field during a partial stripdown.

Unless the chain has been trashed, the tensioner will take care of any "normal" chain stretch. That's its job.

edit: whoops, just noticed QM's similar answer.

 

QM-
I am not sure I agree with the part of your response where you say
the "correct method" does not remove variations due to primary stretch. In the correct method I refer to, you loosens the vvt and tightens the primary chain against the crank to remove slack, then lock down the vvt. After that, the skack on the secondary chain is removed by holding tension with the exhaust gear as it is tightened.