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Valve timing for Dom 99

Submitted by peter_maple on Fri, 20/01/2012
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Heavy Twins

Hello friends.

I would have thought that to measure the valve timing on my 1960 Dom 99,all I would need to do is to set the inlet and outlet valve clearances to that specified and, by use ofa dial gauge and timing disc, find the angle at which the valves begin to be depressed.

On myengine timing disc, produced by R.G.M,there isa note on it stating:

On twin cylinder engines valve timing should be measured with 0.016'' clearance using a 0.003'' feeler gauge.

Could anyone explain how this proceedure works?

Thanks for any help. Peter

Submitted by alan_dawes on Sat, 21/01/2012

Permalink

Peter previously wrote:

On myengine timing disc, produced by R.G.M,there isa note on it stating:

On twin cylinder engines valve timing should be measured with 0.016'' clearance using a 0.003'' feeler gauge.

Could anyone explain how this proceedure works?

There is a fairly clear explanation of how cams work (in the context of the much lauded PW3) here: http://www.peterwilliamsracing.com/pw3cam.pdf

There is a thread about the article here: http://www.accessnorton.com/peter-williams-pw3-cam-t7593.html

I think a read of both will illuminate RGM's instruction.

Cheers

Alan

Submitted by alan_dawes on Sat, 21/01/2012

Permalink

Sorry, I was too hasty. The second link I gave was not the one I thought it was. I can't for the moment find the intended one. I think it might have been on the BritBike forum. I will have a proper look later.

Cheers

Alan

Submitted by peter_maple on Tue, 24/01/2012

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Thanks Alan, read the articles on cams,very interesting and informative but not quite what I needed.

What I should like to know is:

after I have opened up the Valve clearances to overcome the problem of the quieting ramp distorting my timing readings, what do I do with the 0.003 feeler gauge? Do I insert it into the valve/rocker gap then rotate the engine so that the gap closes, continue rotating the engine until it is just possible to withdraw the feeler. Is this the point where the timing disc gives the valve opening angle?

could I not just use a dial gauge to determine the point at which the valve starts to move?

Cheers Peter.

Submitted by alan_dawes on Wed, 25/01/2012

Permalink

Peter previously wrote:

after I have opened up the Valve clearances to overcome the problem of the quieting ramp distorting my timing readings, what do I do with the 0.003 feeler gauge? Do I insert it into the valve/rocker gap then rotate the engine so that the gap closes, continue rotating the engine until it is just possible to withdraw the feeler. Is this the point where the timing disc gives the valve opening angle?

I am not sure which way you are turning the engine but if the feeler can be withdrawn, the valve is closing.

could I not just use a dial gauge to determine the point at which the valve starts to move?

I think the reason for the .003 feeler is to allow for inaccuracy of the base circle. I think that with the valve fully closed, the dial indicator is set to zero with the feeler inserted. The feeler is then removed so the indicator will read -0.003. The cam is then timed in the usual way by rotating the engine and graphing the reading of the indicator against the rotation.

Cheers

Alan

 


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