timing mark

Talk about the E-Type Series 3
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baganz.sven@web.de
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#1 timing mark

Post by baganz.sven@web.de » Wed Aug 19, 2020 12:49 pm

Dear forum colleagues,

I have searched the forum and the WEB to find info about the crankshaft timing mark but I'm still confused.

On my 1971 E the mark A is exactly at 12° after TDC if I turn the engine into TDC.
I have checked the camshaft postition and I also checked if the piston is really at TDC position and everything seems to be correct.

From the info in the forum and the WEB I have expected to find the mark exactly at 6 o'clock what would mean 0° on the scale.

What might be wrong?

Thanks for advice

Sven
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Sven
'71 S3 coupe LHD manual

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lowact
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#2 Re: timing mark

Post by lowact » Wed Aug 19, 2020 2:15 pm

Sven, it may be that your harmonic balancer and gauge plate are not original; my understanding (?) is that all e-type gauge plates folded around the harmonic balancer and the mark on the harmonic balancer was on the front face, NOT on the circumference. Also that the largest number (angle) stamped on an e-type gauge plate was "32". However I do agree that at TDC the "A" should be very close to 6 o'clock, so either you are NOT at TDC or maybe the harmonic balancer has slipped/spun, or is not properly keyed into the correct position?
Regards,
ColinL
'72 OTS manual V12

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MarekH
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#3 Re: timing mark

Post by MarekH » Wed Aug 19, 2020 3:01 pm

Sven,
Yes, it is offset. See pictures. You should be able to see one of the marks even with a big XJS pulley attached.
note the orientation of the four central bolt holes for the pulley relative to the 1A mark at 6 o'clock.JPG
note the orientation of the four central bolt holes for the pulley relative to the 1A mark at 6 o'clock.JPG (193.25 KiB) Viewed 353 times
yellow paint shows 1A TDC mark on damper the timining plate has to line up with this to be meaningful.JPG
yellow paint shows 1A TDC mark on damper the timining plate has to line up with this to be meaningful.JPG (142.76 KiB) Viewed 353 times
The timing plate itself is at 6 o'clock. A sensible thing to do is to get one from an XJS and mount it somewhere where you can see it, having drawn a new coloured line on the crank damper to suit. Mine is next to the water pump on the right hand side.

kind regards
Marek

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#4 Re: timing mark

Post by baganz.sven@web.de » Wed Aug 19, 2020 4:46 pm

Hello Marek,

thank you for your advice.
I have checked the position of the central bolts relative to the A1 mark.
It looks like in your picture.

I will check TDC position again.

Sven
timing 2).jpg
timing 2).jpg (120.22 KiB) Viewed 338 times
Sven
'71 S3 coupe LHD manual

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MarekH
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#5 Re: timing mark

Post by MarekH » Wed Aug 19, 2020 7:44 pm

Finding tdc for a particular cylinder is notoriously difficult, as the crank can be moved quite a lot for very little up and down movement of that particular cylinder around tdc.

If you draw out the firing diagram, with 180' being one full stroke either up or down, when 1a is at tdc, 3a is at 240' before tdc and 5a is at 120' before tdc, with 3a moving down as 5a is moving up (3a moves down for 60' to bottom and then up a full 180' to get to 3a tdc whilst 5a is 120' before 5a tdc and always moving upwards).

That means cylinder 3a is at the same height as 5a when 1a is at its tdc.

This means any small error in judging 1a tdc is magnified greatly if you instead measure when 3a is at the same height as 5a as you are not only measuring crank rotation against when the 3a and 5a cylinders are moving a lot (as they are nearer the middle of their respective strokes). 3a and 5a are moving in opposite directions so any error multiplies up and easily shows up .

kind regards
Marek

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baganz.sven@web.de
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#6 Re: timing mark

Post by baganz.sven@web.de » Wed Aug 19, 2020 8:02 pm

Dear Marek,

Thank you for this explanation.
I'll try this method,
I'm really happy that you share your knowledge whenever someone needs help.

Best regards

Sven
Sven
'71 S3 coupe LHD manual

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lowact
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#7 Re: timing mark

Post by lowact » Thu Aug 20, 2020 1:24 am

On either bank, when pistons 1 (and 6) are at TDC, all the other pistons (2,3,4,5) are at the same level., 75% of stroke below TDC.

I note 2nd photo clearly shows Sven’s harmonic balancer and timing plate are original. I swapped mine for XJ12S3 and for posterity I can report these differences, not Sven’s problem, just related topic:

Below is pic of my removed OEM balancer and timing plate. Note the chamfer around the front edge of the balancer and how the timing plate sits in this chamfer so that front faces of the balancer and the plate are flush, the timing marks are accurate only when the plate is in this position, also less parallel reading error.
Image

Below is pic of the xjs3 balancer and timing plate that I have fitted to my car (plate modified to use both the e-type and xj12 mountings). Marek’s photo is of the same balancer. There is no chamfer on the front edge. There is timing mark on the front face (same as the e-type) that stops where the chamfer would have started, i.e. at the correct position (radius) that the edge of the e-type style of timing plate would need to be, for it to be accurate. There is also a timing mark on the perimeter face of the xjs3 balancer, this is the one that the xjs3 timing plate aligns with. Because it picks up the perimeter radius, not some smaller, inner chamfer radius, the scaling of the xjs3 timing plate is larger, full scale (12+32 deg.) length is 5 mm longer than the e-type plate. All this means, if the timing plate is not correct for the balancer, or if the plate is not correctly aligned, even when correctly set to TDC, the error could be up to 8%.
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Regards,
ColinL
'72 OTS manual V12

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