Cam timing detail question

Getting ready to install a freshly rebuilt engine and double checking cam timing…

The special tool that engages the slot in the cams sits flat BUT not at 0 degrees on the crankshaft damper. It sits flat at 4 degrees AFTER TDC.

I’m thinking that I need to remove the clips and shift the sprockets so that the cam tool engages perfectly when the engine is at 0 degrees on the crankshaft damper.

For those that have gone down this road - is this assessment correct?


Are you absolutely sure the marks on the dampener reflect reality?


Yep. Before doing anything further need to establish TDC using one of the methods detailed in many threads. Doing the same on a friend’s e type at the moment. Paul.

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The first thing that I would do is call the rebuilder about what you found. Have you done that yet?


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As Paul says, Ron - check the ‘why’ with the rebuilder…

They may have deliberately set the valve timing different from the factory specs - and the reason for this may be illuminating. The normal option is of course to use factory specs - but other listers have indeed offset valve timing for specific reasons. If if you find rebuilder’s rationale unsatisfactory - reset…

Valve timing influences the power band of the engine - it is always a compromise. But 4 deg ‘off’ is mechanically safe - I ‘think’…

xj6 85 Sov Europe (UK/NZ)

Definitely “safe”…BUT, probably not the direction to go given powerband characteristics and future chain wear. As the boyz have suggested, make absolutely sure the damper markings are spot-on.

Thanks fellas for the responses. Here’s an update to answer some of your questions:

  1. I used a straw to check TDC versus the crankshaft damper. It appears to be fairly accurate but of course there is the slack in the timing chain to account for. I DID turn the engine back then forward again to try and eliminate the slack so again - the markings do seem accurate.
  2. This is the original damper but the crankshaft was sourced from my spare engine, checked and fitted as the original crank had spider cracks shown in the magnufluxing. so it WOULD be possible that the damper markings for this engine be off a bit but they are after all keyed to the crank. In other words - I’m fairly certain it is reasonably accurate.
  3. I outsourced the machine work but I assembled the engine so I guess there is no option to check with the ‘builder’ unless I interrogate myself. LOL.
  4. The intake side appears to be spot on. The only question now is the exhaust side. The checking tool fits perfectly at 4 degrees AFTER TDC. so the exhaust side would be timed a bit late.

I could remove the sprocket and shift it to adjust, but now I’m wondering if this timing would be considered optimal for some reason. I truly don’t understand valve timing theory. I supposed I could have swapped the parts from side to side, but given that the intake side seems dead-on I’m now wondering if this is simply how it was setup at the factory. The sprockets ARE original to this engine, and I don’t believe they were removed from the center sections as the teeth appeared to be in good condition so they were cleaned and re-installed with new timing chains…

In summary - we know 4 degrees after TDC is not an interference setting, could it be this is the way it was set at the factory for optimal performance?

IF it was me, I would actually set both cams slightly advanced to compensate for future chain wear…half a serration on the exhaust (1.37 degrees) and one full serration on the intake(2.75 degrees). The difference is the large number of worn links between the two cams that will eventually occur.

You did the smart thing by ensuring all the chain slack was after(below) the intake cam. The most important valve timing event is intake closing, btw. It is simple to adjust the serrated plates by removing the bolts, then turning each cam with a rubber-cushioned vise grips.

Simplistic view: Retarding valve timing improves breathing at higher RPM where gases need a bit more time to get through the holes before the valves close.

It often seemed to me that Jaguar would have been wise to retard the cams a little bit for the E-type while advancing them a little bit for Daimler limousines that use the same engine.

Makes it run smoother. But could be the damper moving. No big deal either way.
If you did it it happens because the timing chain is a little slack, did you re-check cam timing after tensioning and turning the engine?

The relationship between the damper TDC and piston TDC is independent of timing chains, Ron. It’s the relationship between damper TDC and cam setting that relates to the chain…

And since you have set the cam timing yourself, and given the damper TDC is correct - you have been sloppy. Set to TDC; the cams should be set identical and perfectly with the setting tool - then the chain fitted and tightened, should not alter the cam positions. This is what Jaguar intended - whether this is ideal for for what you want is another question…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Exactly right, if the cams were set correctly they should both fit the tool regardless of the crankshaft or damper.
If they are off it must have been some slack in the upper timing chain, either unnoticed, or while tensioning the chain, or due to wear.
The cams will shift a bit when the tensioner is adjusted so if you turn the engine and recheck you might need to readjust once more.

If the ‘outsides’ of chain are kept tight when fitting chain to sprockets, David - all the slack is on ‘inner’/idler sprocket chain. And as tightening is done by moving the idler sprocket - slack is taken up without cams moving. Which is all fine in theory - but doesn’t make the practice easier…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

All - Thanks for the replies. The exhaust side was off a couple degrees, so I removed the bolts on the cam plate, the spring retaining the plate to the sprocket and re-adjusted so the tool fits at TDC. Both sides are now the same.

This is why I double checked while the engine is still out of the car; I’m comfortable that this will work well for a stock tune engine.

I would be interesting however for armchair discussion of folks that have adjusted their cam timing for performance purposes. Maybe someday in the future but for now on to additional tasks on the car!

That is correct: on my 1200 IT car, where a
stock cam and no vernier on the cam gear was allowed, I saved the sloppiest, most worn-out chain and sprockets, to do just that.

Exactly :slightly_smiling_face:

Sneaky Ba@(*&Q@D :grinning:


Nuthin’ in the rules said I had to use new timing components…:smirk:

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