TDC

[InfinityJon]

Brain Fog!

Is the keyway on the crank TDC when it’s at 12 o’clock?

 

[Z320]

Here it is 13:47 but this changes from minute to minute 

Sorry me, but you thrown that ball!

I own a 4 cylinder and the key down is TDC of the 1st cylinder 

Ciao, Marco 

Edited July 23, 2022 by Z320

[charlie74]

It’s pretty close but I’m not sure if it’s exact:

 

 

 

edit; the woodruff key isn’t in very good focus but you can see it on the crank…

Edited July 23, 2022 by charlie74

[harlequin]

3 hours ago, charlie74 said:

It’s pretty close but I’m not sure if it’s exact:

 

 

 

edit; the woodruff key isn’t in very good focus but you can see it on the crank…

I do something similar to Charlie's photo but with an exta bolt that prevents the piston rising to the top of the stroke, with the degree  disc on the crank set to about tdc I carefully turn the crank untill the extra bolt stops the piston, then take the reading from the guage. Next slowly turn the crank in the opposite direction untill the piston again stops and take the reading. TDC is then midway between the two readings.

George 

[john.r.davies]

To supplement this discussion of where it is and how to find it, may I ask anyone who does find TDC using any of the piston height methods to then check where it is according to the crank pulley?

 As you may know, I have a great interest (and, if I may say  so, expertise) in the crank dampers that Triumph fitted to their sixes, inside the pulley.        Their function as dampers after fifty plus years has to be in doubt, and I can test that, but worse is when the rubber ring in the pulley looses adhesion on the metal parts.      This allows the outer "inertia" ring to move on the hub, making nonsense of the TDC timing markings on the outer edge of the ring.

I surveyed Triumph owners a few years ago, and found 20% of responders had seen this potential; disaster.      I'd like to update that survey, so please let me know if you find your pulley out of line?

 John

PS  I hope to be at the Oulton Park Gold Cup, by kind permission of the Red Rose Group, so if you are concerned please see me there!

Edited July 23, 2022 by john.r.davies

[harlequin]

2 hours ago, john.r.davies said:

To supplement this discussion of where it is and how to find it, may I ask anyone who does find TDC using any of the piston height methods to then check where it is according to the crank pulley?

 As you may know, I have a great interest (and, if I may say  so, expertise) in the crank dampers that Triumph fitted to their sixes, inside the pulley.        Their function as dampers after fifty plus years has to be in doubt, and I can test that, but worse is when the rubber ring in the pulley looses adhesion on the metal parts.      This allows the outer "inertia" ring to move on the hub, making nonsense of the TDC timing markings on the outer edge of the ring.

I surveyed Triumph owners a few years ago, and found 20% of responders had seen this potential; disaster.      I'd like to update that survey, so please let me know if you find your pulley out of line?

 John

PS  I hope to be at the Oulton Park Gold Cup, by kind permission of the Red Rose Group, so if you are concerned please see me there!

Hi John

After checking TDC as described above I found the timing marks to be spot on. I believe the pulley to be the original 1972 item (I have owned the car since the mid 1990s) and the mileage is somewhere between 200 and 300k.

George 

[john.r.davies]

Thanks, George, that's one in the 'Good' column.

It is a credit to Triumph that so many of their dampers are still intact after so long.    Even moderns have not been so long-lived (Mitsubishi recall, Montrero, 2000)  But their function as dampers, as the rubber inevitably hardens with age, heat and oil, remains in doubt without testing.

John 

[InfinityJon]

My reasoning behind asking is that I am fitting a trigger wheel and need to mount the missing tooth at 60 degs before TDC on the back of the crank pulley. Having fitted my head I’m not inclined to remove it so wondered if there was an easy check. 
 I know I can make up an adjustable Hall effect sensor mount to soak up the odd degree but can I assume that for the purposes of mounting the trigger wheel to the pulley, TDC shows the woodruff key at 12 o’clock?

 

[RogerH]

Hi Jon,

I would not rely on the woody key.

Many folk use a modified sparky plug.

Remove the the ceramic and fit a rod with a rounded end.

Rotate the crank until the piston hits the stop - taking degree wheel reading.

Turn crank back until it hits the stop again - TDC will be in the middle of the two readings.

 

Roger

[john.r.davies]

The 'other' way is to use "Equal Lift on Overlap".   This relies on the  fact that TRiumphs use a "symmetrical" camshaft that must be installed at TDC, with the two valves of the the non-firing cylinder equally raised, one going down, one up.

The normal method is to use two dial gauges, but recently I found an easier way.   See: A new method of cam timing - Engine and Ancillary talk - Sideways Technologies (sideways-technologies.co.uk)

 Find this point on N0.6 and you have TDC, which of course will be TDC on No.1

John

Edited July 24, 2022 by john.r.davies