66 S1 Timing Check Question - Timing Tick Marks

This all started with some carb tuning a few weeks ago. I am now dabbling into a timing check. Following the SM it states to manually turn the crank until the damper pully 10 degree tick mark lines up with the pointer mounted to the sump. Then check the dist rotor which should be pointing close to the #6 cylinder on the dist. When I do this on mine the rotor is approaching #6, but the piston is no where near TDC. I hooked up a test light between the coil (my wire is yellow) and ground to find the point where the contact closes at #6. I rotated the crank until the light turned on and found the timing marks on the damper where about 70deg past the pointer on the sump. It is not even in a good location to put a timing light on it. I removed the #6 plug and placed a dowel on top of the piston (carefully) and rotated the crank until it leveled out at TDC (eyeballed). My guess is on the order of ~10-12deg before TDC based on when the light turned on and when the piston hit the apex. So I am wondering if the timing was set up to another piston. I thought the damper was notched to the crank, hence the #6 reference in the manual. Help needed here is how I could accurately set the timing not having the damper marks for a reference. Thanks in advance, Skene

If you are really wanting to get 1 or 6 on TDC it’s really easier to cut two equal length dowel rods and drop them into 2 and 3 or into 4 and 5. When they are at the same heights, 1 and 6 will either be at TDC or BDC. The pistons aren’t moving much relative to crank angle when they are at to or bottom. If your balancer doesn’t indicate TDC on the pointer when the dowels are even, you might have a keyway issue.

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These harmonic balancers are known to move on their rubber “suspensions” when they get old. Perhaps your timing marks have moved?

Damper slippage sounds most likely to me as well…and you can only check timing using either #1 or #6 since each cylinder fires 120 degree apart from each other.

Damper from a later engine perhaps? Pointer was in a different place on later engines.

There is even a Jaguar tool for that:

But the dome on the piston and the offset of the cylinder & plug holes can confuse matters a bit.

I prefer a piston stop:


Thanks for the ideas on the tooling. It seems strange that the damper would slip. I thought it was notched, but I have not had it off. The motor is original unless something was done with the damper pully in the past. The motor was modified for drag racing at one point by a PO. I guess one option would be to make some new marks referencing TDC on #6 using the tooling and verify/adjust it from there. I could make a template from the existing marks on the pully, but it would be nice to use the original factory marks.

The damper is keyed to the crank, however if it is like the 3.8 one, it’s actually two pieces bonded by rubber. One keyed to the crank and the other, having the timing marks. When the rubber deteriorates enough, one part slips in relation to the other. When that happens you have to replace it with a rebuilt one. This is just based on the 3.8 which I’m familiar with.

You could attach a timing dial indicator, but that doesn’t solve the issue with a deteriorating damper which can fly apart damaging the car.

This assumes that it was assembled correctly with the woodruff key installed. The only way to find out is to remove the part. If you’re confident that the engine is set at TDC and the damper doesn’t indicate that, then something is definitely wrong.

This interesting so what I am hearing is the two disks can slip relative to each other. Mine looks like the one in the picture below or the same as in the service manual So the inner one with the marks is not keyed to the crank but bonded to the other outer one that is? That is a bad design if so. The one with the marks should not be able to ever move relative to the crank. My issue would make sense if that is the case. I do know #6 is firing before TDC per the test light static check. Definitely is not matching the damper marks.


I pulled an engine out of a 1971 XJ6 that had timing marks 60 degrees out. The damper shows no sign of slipping - the rubber is completely intact and I cannot make the centre part move relative to the outer. Seems peculiar to me. I made up rods as in the earlier posts to get cylinders 2,3,4,& 5 all at the same height.

I’ll have to let someone with a 4.2 answer that question but it’s definitely possible that the larger segment with the timing marks can slip on a 3.8. It is bonded to the cone that engages the crank. If memory serves it isn’t even held by the bolt, otherwise it couldn’t perform it’s intended function. The rubber is meant to have some flex. But eventually the rubber gets so petrified it doesn’t flex and can shear.

I’d set up your TDC again if there is any doubt using a mechanical method, and if you don’t see the TDC mark on the damper very close (close enough so that it might simply be the pointer which is out of adjustment) then something is not right. Either the key is missing (or perhaps sheared) or the damper is broken.

Here’s a photo of a damper off a 4.2L:

Note that it consists of two pieces of steel, with a rubber annulus bonded between them. The inner steel part is keyed to the crankshaft. The outer, steel piece is attached to the inner piece by the bonding of the rubber. If that fails on either part, the outer part can rotate relative to the inner. Hope this helps.

Thanks David. This picture and description helps a lot. I was looking at it incorrectly. So the inner hub is keyed, and outer is bonded to the inner. It would seem that if the bonding failed or the outer piece started to slip then the pulley could come apart. If I am looking at this correctly the pully for the belt is mounted to the inner damper hub, therefor there is really no stress on the outer part other than its own mass. What is that silver piece with the notch on it?

That cone slips over the crank, and is keyed to the crank, then the damper slips on, and is keyed to the cone. I think they call it a split cone. I’m not sure the benefit of such a mounting system. Modern fluid dampers just slip straight on the crank.

I suspect the cone was used because it provides a tight fit for the damper without the need of a tool to mount the damper. You can buy competition dampers for E Types from the usual’s. I have one on each of my cars. They are a very slight interference fit on the crankshaft, without a cone and are installed and removed with pullers and pushers. Inconvenient on an assembly line?
Can the rubber on a stock damper deteriorate to such a point that the outer part rotates at a different speed, and not come apart shortly thereafter?

In respect of dampers and timing marks being out of place. At some point Jaguar switched from the bottom timing point to a point on the left side of the engine, and changed the damper appropriately. As I recall these dampers are interchangeable with the original 4.2l

Just seems like a poor design if there is any chance of the timing marks to move, well it was 50+ years ago. This damper should have been one piece. Now it appears mine are useless. With #6 at TDC my marks are on the right side (passenger side) on the order of 70 - 90 degrees from 0600 where they should be. So approx 0800 to 0900 looking at it from the front of the car.

I suggest you mark the damper at TDC for the pointer you have, you might consider grinding a notch with a dremel and filling with white paint.
Then see if if it moves. If it moves, replace the damper ASAP. You do not want the outer ring coming off at speed…

I’ve never seen one apart so I’m not sure what the interface between them looks like. Mine was quite cracked and petrified at the point I sent it off for rebuild but it had never once slipped. I was warned about this 20 years ago and took the precaution of painting a thin line crossing both segments so I’d have a permanent visual clue to warn me.

I think you’re likely correct. The cone does add some convenience. It’s one of the reasons I paid for a rebuild rather than buying a nice fluid one. All it takes is a tap normally and it falls right off.

On my S2 4.2 the timing marks are on the inner portion of the harmonic balancer - which I think would mean they could not slip even in the case of a failure of the balancer.

I realize your S1 is different in that the timing pointer is at 6:00 - but which half of the pullet carries the marks?

Ahhh nomenclature. Your timing marks are on the outside of the harmonic balancer RADIALLY, which counts for this discussion.

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