Cam drive sprockets

Hi all
So I’m just about finished with my valve adjustment and repair of cam oil feed line, when I noticed something.
According to an article on cams, the drive sprockets I have are not good. They are the middle one in the attached picture, and the article states: “ The Middle one is the one to watch out for as it tends to slip causing valves to get bent for as it does not have as many teeth and the teeth it has are spaced wider so have even less tooth to tooth contact. I have not been able to trace out a number for this from the Jaguar parts book. It seems to show up in the 1969 model year engines. Jaguar stopped using it after a very brief time and went to the four bolt configuration. If you have the scalloped 2 bolt ones on your engine, throw them away and replace them with the round ones.

So… how serious is this? Is it as bad as it sounds? Should i do something immediately or is this something that can be done later.

Also, what’s involved in replacing these?

Thanks for any input.

Once it is bolted down it cannot slip.

Hi Robert…I replaced mine…as far as i know they could slip…the part you show is bolted to the end of the camshaft but it sits inside the chain sprocket only held inplace by the tiny teeth and spring retainer…so its actually the outside sprocket that could slip…looking close at the scalloped plate on mine the teeth also did not look as good a fit into the outer sprocket as the new replacements…The problem with a question like this is you will always get two different opinions…Steve

Doesn’t the bolt go through the plate with the teeth on it though?

Hi Andrew…the bolts fix the plate to the end of the camshaft…so it cant move but the chain sprocket is only held onto the plate by the teeth and spring retainer so if the teeth wear the chain sproket could just spin around the plate

It’s still a crush fit onto the camshaft in that the sprocket is held firmly between the end of the cam and the plate by the torque on the nuts. It’s not just the teeth that are holding it; they are just a vernier arrangement to allow you to set the timing. I grant you there are fewer teeth but it would take an enormous amount of force to shift that even if there weren’t any teeth at all.

The picture and quotes come from the Georgia Jag site. Dick knows his stuff and I’d be hesitant to disagree with his experience, however looking at another pic from the site the teeth look pretty substantial. When you compare them with, say the splines on the torsion bars they don’t look puny.

Nevertheless I concede that Jaguar obviously didn’t like them if they got rid of them.

Changing them for full circle ones wouldn’t be too difficult although you might need to remove or at least loosen the cams to get clearance.

My car (69 S2) had those scalloped sprockets - when Dick Maury (author of the above) rebuilt my engine he replaced them with the earlier full circle (2 bolt) variety.

I do not think you can swap them easily - even with the cam out and the upper chain tensioner fully loose there is not enough clearance. There may just enough clearance to get the scalloped version out but not enough to get the full circle in. It is very close but a little more slack is needed - possibly removal of the upper chain tensioner - though I did not go that route:

[Edit: looking at it now, perhaps removal of that one cam cover stud would have helped]

I learned that some actually cut a portion of the slotted support away (example highlighted in red) to do this. Possibly harmless but a bit extreme in my opinion:


Personally I’d replace them. I replaced my original ones 20 years ago along with the gears just as a matter of course, because they were so old, and they were the full round style. But the point may be moot because I was looking for timing components a couple weeks ago for my own engine, and noticed that cam gears and adjusters were showing as unavailable at both SNG and XKs. Hopefully it’s not a permanent situation.

As Geo mentions, even with the chain fully slack you can’t disengage it from all the teeth on the gear simultaneously so you can’t easily slip the gear out to remove the adjuster. If the chain happens to have a master link you’re golden, just open it over the gear and pop the gear out. If not I guess you could use a chain breaker and feed a new chain through that has a master link.

Edit: SNG is now showing low stock of adjuster C34034, but still no sprockets. Are the sprockets the same for both types of adjusters? Not sure how that works with the wider teeth on the oddball one. Maybe it just engages every other tooth on the sprocket?

I was just on SNG and found these… it looks like an assembly which would solve the “won’t fit” problem and replaces it with a “ how am I going to do this without dropping a part in the engine” problem

Thanks for all the photos and explanation! I’m not sure if removal of the studs would create more room between the chain and the top of the head. I agree with you, cutting the bracket seems like a terrible idea…

I think the originals can be disassembled via the circlip. But even if you could get it apart, I’m not so sure the new ones come that way. I think the pin is swaged to the adjuster plate so you wouldn’t be able to get it back in that way.

My suggestion to break the chain is likely the only way to do this without major surgery. My head was off and I still couldn’t easily finagle cam gears out without breaking the chain. I didn’t spend a lot of time cogitating on it though as the whole thing needed to come apart anyway.

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ah… sometimes this project makes ME want to do that.

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My engine rebuilder, who knows infinitely more about these engines than I do, recommended replacing the scalloped sprockets with solid ones. When he explained it too me it made perfect sense. So I agreed for him to do it while the engine was being rebuilt. .

Does this mean every engine is near imminent failure and every owner should run out this morning and replace their scalloped sprockets with the other ones? No, I see it as a replacement if you are doing something to the car where you have easy access to sprockets anyway. You are buying a bit of peace of mind.


Cogito , ergo sum

According to Decartes, if you don’t cogito you don’t sum. So I guess I only half am because I run on instinct often.

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SNG is showing the sprocket as a loose part…

Huh, okay then you might make it work. Just stuff rags down on both sides of the gear in a way that you can retrieve them later in case the clip tries to fly south for the winter. This assumes that you have room to access the circlip with a tool. Big if, I’d check it before ordering.

Edit, Geo’s photos don’t bode well though. His was disassembled and it looks like he was unable to slip it in.

Yes, but his had the shaft attached. If it’s just the sprocket it should slide down vertical, then mate up to the separate shaft. Although it doesn’t look like SNG have the shaft…

Ah, yes, he had the swaged variety. FWIW, those pins don’t actually do anything except to assist in timing and installation of the part. Basically it keeps the gear aloft while it is apart from the cam. Once bolted to the cam it just sits there and spins with the gear. So you could just use a temporary bolt to hold it up for you while you time it.

You could also possibly reuse your original pins and clips assuming they fit on the new adjuster plate.

I managed to remove my sprockets and adjuster plates(with swaged shaft)…no cutting no removing camshafts or studs or undoing chain…you have to remove fixing bolts on both camshafts and tap both sprockets off the cams…remove both retaining spring clips…then just care needed to jiggle them out…and fit them back in…ps i might have had to move crank a bit to get slack on the chain…cant remember exactly but the did come out…and back in…Beware if moveing crank as your camshafts are not attached…so make sure you understand what you are moveing or you could and up with bent valves…Steve

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It’s really not a big deal to remove the cams - we all have to do it to adjust the tappets. Once the cams are out, you have complete access to BOTH sides of the adjuster plate, and it should come out easily. And once the cams are out, you can turn the crank all you want.

Ray L.