Ahh, Okay, I get what you were describing now. The end of the camshaft is actually a straight shaft (and keyless, but no taper) and the fit is called a machine fit or close fit. The thickness of the sprocket is slightly larger than the length of the machined endshaft, so the bolt "pinches" the sprocket in place against a machined collar under torque (and why the torque is so great).

Never heard of an infinitely variable taper - a mechanical impossibility; but, it it could be said that any taper has an infinitely variable diameter.

An infinitely variable taper is the mechanical equivalent of Deja Vu all over again Ha, ha...you can probably see why after a few minutes I was looking for a couple of aspirin LOL!

 

Like I said, I'm ****- I use the flex plate lock to get the crank position right on the gnat's *** with the primary chains tight on the non tensioned side. I use the cam lock tool to get perfect alignment of the cams.
Afterwards I put my hand on the intake manifold while the engine is running to feel how smooth it is running. I also look at the rear corners of the open hood to see any vibration.
Like I said, I'm ****- it comes from the disciplines learned from many years of building engines.

 

Once you set the cam flats on the same plane so the cam tool can be used, the crankshaft never moves until the new tensioners are installed and exhaust sprockets/chains reconnected. Why pin the crankshaft?
There is no more or less accuracy in the relationship between the crankshaft and camshafts with or without the crank pin if you follow this process.

I understand pinning the crankshaft as a matter of rote process, but if you think it through at a higher level, it is simply not necessary.

 

I don't consider the crank lock a rote process nor is it to prevent crankshaft movement. It is a matter of assuring proper crank position from the start. The cam flats can be in alignment enough to put the tool on with the crank still several degrees out.

 

If it satisfies you then the extra work is worth your effort. No problem doing it.

All the Best

 

The tools needed to keep the Jaguar timing can be purchased, from http://www.welshent.com/index.php?cPath=1110&page=1

Part # 303-530, 303-531, 303-532

Camshaft setting, Crankshaft Setting, Timing Chain Tensioning

Procedure for use found in JTIS Issue 21

Hope it helps

 

Last month I purchased a '98 XK8 with 53K miles. I pulled the valve covers this afternoon, and sure enough, my XK has the original, red type 1 secondary tensioners. New secondary tensionsers and gaskets will be on the way shortly.

A quick question with regards to replacing the secondary tensioners using the "remove the exhaust cam" method. I understand that the secondary timing chain will not move if properly zip tied to the exhaust sprocket, but how does one guarantee that the exhaust cam is reinstalled in exactly the same position (and relation to the intake cam) when the cam caps are torqued? Is that even a concern?

Quote:

Originally Posted by WhiteXKR

There is a theoretical concern of mis-synchronization and incorrect pretension which can result in poor idle, but I have not come across anyone who has reported this actually happening.

Any thoughts would be appreciated and thanks in advance.

 

You cannot guarantee they will be exactly aligned without the cam alignment tool. A number of us have used the "remove the exhaust cam" method with no problems. If the engine is otherwise in good shape, it should be very, very close with no perceivable effect on performance. If you will feel better with a guarantee, you should get the alignment tool.

 

The zip tie method is actually more accurate than using the cam lockdown tools, IF the original setup was accurate. Using the lockdown tools has an inherent flaw and I've seen a few jobs done badly. The problem comes when the bolt on the end of the exhaust cam is being tightened on reassembly. If the chain sprocket is "loaded" in the wrong direction (wrong side of the tensioner), then even with the lockdown tools the exhaust cam will be a little off when the tensioner pin is released as the relationship of the sprocket to the cam shaft is infinitely variable.

In other words, if the tension is put on the drive side of the chain instead of the driven side, the slack will be on the fixed side of the tensioner. When the pin is released, the exhaust cam will advance so the slack is taken up on the correct side, putting the exhaust cam slightly off.

This cannot happen using the zip ties as the exhaust cam bolt is never loosened so, in reassembly, the exhaust cam will end up exactly where is was before in relationship to the intake cam. This is true even if the crankshaft was accidentally rotated slightly while the exhaust cam was out of place.

After all of this, I still prefer using the correct factory tools, but the zip tie method was accidentally brilliant.

 

Steve: I agree with the above with 1 VERY minor exception. If the chain has stretched since the engine was originally assembled, the "Cam Clamp & Sprocket Unbolt" method could correct for the stretch.

 

Yes, in theory, I agree.

The correction for chain stretch would be equal to less than one half the total chain length (just the distance between the last engaged tooth on the intake cam to the first engaged tooth on the Ex cam on the DRIVEN side only) for the total delta in chain lengths (new vs. old).

Any chain stretch on a chain this small with this light a load is only going to be measurable with a micrometer. There is almost no resistance in this chain assembly because valve spring pressures are both waxing and waning simultaneously. If anything, because the AJV8 valve train design is asymmetrical, the real effect on chain wear comes in the form of a push/pull bobbinlike action that occurs every cycle which creates a slight harmonic imbalance (well known by the designers BTW, but a tradeoff for better valve entry angles thus better cylinder head squish patterns).

I'll bet that the change in sprocket position on the exhaust cam due to chain stretch wouldn't be visible by the nake eye. More people will make a much larger error when trying to attain the correct torque while hold the exhaust sprocket with the spanner.

 

Yes indeed. When I tightened the Sprocket Bolt (while holding tension with the Chain Tensioning Tool), I used a 10mm Allen Key and a 1 foot length of electrical metallic tubing and made it "Plenty Tight". Torque Wrench, Who needs a stinking Torque Wrench!

 

After I saw the sprocket to cam connection and the size and threads of the bolt I made it about as tight as I could get it, never mind torque specifications. I am surprised that someone hasn't reported a failure in that connection.

 

I really think the "pinch" is very sufficient...another witness to the fact there is very little resistance to drive the valve train.

 

I have a question with regards to "the timing chain tension problem". I have a 2001 XK8 with 57,000 miles on it. I read that the tensioners need to be changed, but does that mean just the top tensioners as above on this post, OR do you also have to replace the lower much larger tensioners??? which is much more complex and expensive. can i get away with just changing the top tensioners as the above post??
Many thanks for your help,

 

djp, the consensus around here is that the secondary (top) tensioners are the most problematic. I can't recall hearing any primary tensioner failures. If it were me, I'd just do the secondary ones and be 99.5% confident in the longevity of that engine...treat her good!

 

Thank you very much, I will see how much it will cost. Thanks again for all your help!!!

 

I also have a 2001 XKR w/ 63k, and want to do this precedure to prevent an expensive problem down the road. Does anyone have a picture of the ziptie on the sprocket and chain so i can have a visual? I would be grateful for any assistance. Also, thankyou whitexkr for the part numbers.

Ryan.

 

I have replaced many tensioners and I have seen some primaries with cracks but never a complete fail, never done the zip tie method before, not sure I like the idea, I much prefer to lock the cams down.

If anyone is interested I do have CAD drawing file I done of a full tensioner tool set, I was going to make my own but ended up buying them instead

 

Attached is a write-up on the zip-tie method. Also attached is a photo of the secondary tensioner. The lower sprocket (at the bottom of the photo, in the foreground) is the exhaust cam sprocket. Simply zip-tie the chain to a hole in the exhaust cam sprocket per the instructions.