…not as an inherent design flaw.
Install the lobed ones correctly*, and they won’t be a problem.
My point exactly. 20
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Why would both parts have teeth machined in then if only the clamping force was required to hold the chain sprocket on to the camshaft…it would be far earier to adjust cam timing with out any teeth…however…if your going to have teeth far better to have an exact fit matching set…the scollop shaped plate is far from an exact match to the chain sprocket…Steve
It’s a vernier just like the torsion bars.
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Nothing like the torsion bars…it being suggested that the teeth arnt really necessary and only the clamping force is required…hence my question why are teeth needed if only clamping force is required…Steve
Not sure where that came from, but it’s a combination of both. Pure clamping force, alone, would not suffice.
The teeth are needed during the set up period to ensure the cams are in the correct position.
I agree with Paul. I can’t see that clamping alone would allow the sprocket to drive the cams over a period of time. It makes sense that the sprocket drives the adjuster which then drives the cams. If the bolts were not tightened properly, then play would allow movement which would allow the gearing to wear and eventually shear the teath, resulting in a mess.
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Same here, much better to have a positive locking/locating method.
Aftermarket adjustable cam sprockets for 10000rpm+ motorcycle engines or American V8s are simply slotted for adjustment purposes. No teeth to align. The are secured with 4 to 6 bolts.
If there’s flaw in the '69 version it might be the limited clamping force provided by just 2 bolts.
That said my valve opening timing was within 1 deg of spec, so I did not “open” the sprocket to adjust. I Loctited, torqued, and safety wired the bolts. Been fine (so far).
Rather than replace, couldn’t one add additional bolts to further secure the sprocket to the cam?
Obviously done on the work bench. My recollection of the assembly is that the bolts have to loosen for the teeth to start to “work” and eventually overuse/strip.
MANY engines, including virtually all BMWs, use nothign but bolts to retain the cam sprockets. On my late-model BMWs, both sprockets are held by only 3 small (5-6mm) bolts.
On the XK, the teeth are only an assembly aid, so the timing does not shift as soon as you loosen the bolts. At a minimum this makes shimming the tappets a bit less work.
Regards,
Ray L.
BTW - If you have a bolted connection, as here, plus some other means of alignment, like the little teeth, dowels, etc., if there is ANY movement whatsoever between the parts, then the bolted connection is accomplishing essentially nothing, and you are entirely depending on the teeth to keep things together. And, worse, the bolts WILL inevitably come loose, as whatever movement there is will inevitably wear the thrust surfaces causing the bolt tension to gradually (or not so gradually) reduce to zero over time. Conversely, if the bolts are properly tightened, there will be NO movement, and the teeth are completely unnecessary.
The problem I see with the scalloped adjusters is that there are only two bolts, and the are located 90 degrees from the teeth. The contact surfaces between the adjusters and the flange on the sprocket are rather narrow (~3/4" or so?). I can imagine there being significant axial forces attempting to rock the sprockets along the axis of the toothed section, which could tend, over a long time, to wear the edges of that small contact patch, which would also tend to possibly allow loosening the bolts. Certainly the stresses on the flange are FAR more concentrated with this design. Had they used four bolts, I think there would have been less of a problem. The previous design, even the two-bolt style, would not have this problem, as the 360 degree flange does not allow for any rocking whatosever of the toothed disc.
Even so, the way I read the quoted section of the manual, there really is no problem IF the bolts are properly tightened, and wired as a backup.
Regards,
Ray L.
Not sure how many here have worked on the V8 Jag engines. The cams (4 of them) are held in place by a single bolt torqued into place. The gear sprocket goes over the end of the cam and is held in place by an alignment tool until torqued. No keyway, lock wire, serrations or anything, just a bolt and friction. The XK engine has serrations to set up the cam and keep the timing if the cam is removed. If it was not a problem with the 1969 wheels, then Jaguar would not have switched back so quickly. I have seen them slip and change timing on cars that I know were well maintained. If you have them, I recommend you replace them. Of course you can wait and might get lucky. Worst case is bent valves and possible piston damage but best case is replacement and no problems.
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Thanks for weighing in on this discussion Dick, as you’re probably the only one of us with actual knowledge of the problem.
What would you advice to Bob Thomas, the OP, be? Should he replace them now or can it wait until the head comes off in the future?
this is kind of like the plastic tensioners in the early V8 cars. Run perfectly fine until they break and some go a long time without any problems “yet”. Then big problems. Can’t speak for anyone else but I would not drive my car with these in it. To easy to fix vs fixing the results of what can happen.
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There you have it Bob. Dick speaks from real world experience, whereas I speak from my comfy chair of subjective opinion.
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I speak from a loooong time ago: I got out of “da bidness,” before I ever saw any issues with the scalloped sprocket centers.
Obviously, Dick has seen failures, and Jaguar, unbeknownst to me, saw the issue, too.
If the SIII sprockets are compatible, I have two sets, for free!
Different part on the V12 I think.
I’m sure that good used ones are available, and Bob if not we have a couple of dozen, but we’re in Australia.
Series III XK engines…
Apparently I’m going to need a set when it comes to it.