camshaft timing HELP!!

[TimW]

Hi
Just about to install a TR5 PI cam into a mk2 2500pi lump.  Can anyone tell me the timing figures?
Thanks
Regards
Tim

[JohnD]

You don't need "timing figures".
Do it by the "Equal Lift on Overlap" method.

Most camshafts, inc. Triumph ones, are symmetrical.  The Inlet and Exhaust cams  have the same shape and those for one cylinder are spaced symmetrically about the TDC position.  Also, the cylinders are in pairs, exactly 180 degrees out of phase.    So, as No.1 cylinder reaches TDC on the firing stroke, No.6 is finishing the exhaust stroke and starting the inlet stroke of a new cycle.

Method:
Set the crank at TDC for No1 and No.6.
Set the camshaft so that the cams for No.6 are both equally lifted - Exhaust going down, Inlet going up.
Fit the cam chain.
Voila!
Trust me.  That is all, and your camshaft will be perfectly timed.

John

[TimW]

Thanks John
Will set as you say tomorrow after work.  Thanks again for your help.
Regards
Tim

[CharlieB]

Do you need two dial gauges to do that John?

[Gt6s]

Overlap at TDC.

SOOOO EASY !

[TimW]

Gt6s wrote:

Overlap at TDC.

SOOOO EASY !

Like most things in life it's only easy if you know how!!

[JohnD]

Two dial gauges can be useful, with a stand each of course.
They cost from peanuts to �15 plus �10 or less for the stand.
I suppose you could mount two on one stand but life's too short.

You don't NEED a dial guage.

Set the crank TDC with a protractor and a piston stop.
Piston stop is a device for arresting the rise of the piston in the bore at a fixed point.
Picture of mine below.  A bolt on the angle iron projects down the bore, stops the piston.
Note the angle from the protractor against the wire pointer.
Turn the crank the other way and note the angle at the same point.
Now TDC is exactly halfway between those two points.
Turn the crank to that point using the protractor.
This is better than a dial gauge, as the dg shows that the piston stops, completely still, around TDC while the crank  rotates a few degrees.
So where is TDC?
If the stop is about halfway up the bore, then the piston is moving at maximum speed in mms/degree, so accuracy is maximised.

Likewise, for setting the camshaft a vernier depth guage is better than a dial gauge.  You only need one and no stand; �10 on eBay.
Place a cam follower over each of the cams for No.6.
Adjust the camshaft and measure the height of each cam below the block face with the depth guage until they are equal.
Dial gauges are best for showing relative movement, not absolute distance.

As with any new technique, take your time, and practice doing it.  Get familar with it, before you do it for real.

Good luck!
John

[Pete Lewis]

thats fine with the head off  
to get the lets call it overlap of the tdc postion on the cam we used a protractor  and measured the degrees of turn for a set rocker lift ( 0.020" with a dial gauge ) do it for rise  and fall..  then halve the resulting degrees  and position the cam to this point , we did  to rely on the tdc crank marker .  otherwise 1/4 tooth is easy error to have but not realise   Pete

[TimW]

John
sorry mate i still don't quite understand.  Where do i start from? do i set the piston at approx tdc and zero the timing wheel? and then fit the piston stop or do i just fit the timing wheel at any position with the piston at any position and then carry on as per your instructions?  Does this make any sense?????

Thanks for all you input

Regards
Tim

[JohnD]

Tim,
No probs.
Fit the timing wheel (protractor) to the crank.  Make sure it is firmly fixed and won't rotate except with the crank.  Some packing pieces either side, eg large washers.
Fit a pointer of some sort.  The wheel is a long way frorm the front face of the block, so 'eyeing' it is prone to error.  My pic shows a length of wire, bent to shape.  Use thick, stiff wire!
Fit your piston stop to No.1 cylinder with the piston at the bottom of the bore.   Arrnage it so that the piston is stopped a little above halfway up the bore.
Now turn the crank one way, until it meets the stop.  Note the reading on the wheel.
And the other way, note the reading.

There is no need to align your wheel in any way - you are just using it to measure that arc from stop to stop.  Then, TDC is right up the middle.  Does this diagram show that the actual position of the stop doesn't matter?

NB many timing wheels show 0-180 twice, not 0-360 degrees.   You need to keep clear in your mind where the arc is, if it goes from one 0-180 to the other.   It may help to set it roughly so that 90 is more or less in the TDC position, and set your stop so that the piston is arrested less than 90 degrees before and after TDC, so you stay within one 0-180 range.  
  Now let's say that the stop positions are at 57 and 138 degrees.   That arc is 81 degrees, and TDC will be halfway along it.  So TDC is at 57 + (81/2) degrees, or 97.5 degrees.

Take off your piston stop and turn the crank so that the pointer is as 97.5.  "You have now reached your destination"!

Please ask again if that's not clear.
John

[TimW]

Thanks John
much clearer now.  I will try it tomorrow and let you know how i get on
Once again Thanks for the help.