Valve timing checking

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Paul Gasson
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Valve timing checking

Post by Paul Gasson »

I am hopefully about to close up the engine on my 1950 NH project and thought it would be a good idea to check the valve timing, out of curiosity and to see if wear in any of the parts has made the figures vastly different from the standard values. My question is, what should the valve clearances be when checking? I cannot see anything in my copy of the Waller book and I searched the documents in the club files and could not see anything. I’m guessing either standard running clearance but I thought I read 0.020” somewhere. Could anyone help me with this?
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keith.mettam
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Re: Valve timing checking

Post by keith.mettam »

This is the info I have:-
Ariel cam timings 1938 to 1950.jpg
Hope it helps. Cannot remember where it came from, sorry !
All the best, Keith.
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Roger Gwynn
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Re: Valve timing checking

Post by Roger Gwynn »

It is difficult to measure the exact point of opening, which is why larger clearances are usually used for valve timing. The best check is the point of maximum opening, which is more important anyway. That point is half way between the figures given for opening and closing and again it is difficult to be accurate about the max opening because the movement is slow. Take a reading from the degree disc at .060" before and after fully open, half way between is the point of max opening. Years ago I measured many unworn original cams and never managed to obtain the figures in the books at that time I hadn't learnt about using the lobe centre angle method outlined above.
Roger Gwynn, Membership Secretary, curator of the Machine Register and the works drawings. Director of Draganfly Motorcycles, Craven Equipment and Supreme Motorcycles mostly retired.
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cmfalco
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Re: Valve timing checking

Post by cmfalco »

For what it's worth, the following two figures show the valve timing I measured on my 1928 Model C, with the arrows showing the book values of the opening and closing angles.
ValveTiming052.jpg
ValveTiming052.jpg
The graphs show the difficulties of using the measured lift, the midpoint, and the book values. But, if my data are representative, they show that the lift measured at 0.010" comes closest to reproducing book values.
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ValveTiming04.jpg
david.anderson
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Re: Valve timing checking

Post by david.anderson »

The current industry accepted standard for quoting valve timing is at .050” lift as it is clear of any ramps and permits a reasonable comparison between cams.
2 different A7-642 cams that I checked at .050” lift gave the following figures. 2 49 51 2 and 3 45 52 -1(negative figure). For the first cam the intake duration is 231 degrees, Exhaust duration 233 degrees, lobe separation angle 114 degrees, inlet centreline 113.5, exhaust centreline 114.5, inlet max lift .317” exhaust lift .320”. So that is virtually a straight up valve timing.
Ariel quoted the valve timing for the A7-642 cam at .010” lift as stated in the owners guide and see also the table by Keith above.
2 different cams that I checked at .010” lift gave the following figures.
29 76 77 32 and 26 67 79 24 whereas Ariel quote 18 68 63 23, so in effect both cams are a little hotter than the Ariel specs.
When you check the valve timing it is best to remove the outer valve spring as the strong outer spring tends to affect the engine rotation and use a socket and bar on the engine sprocket nut. After determining tdc and setting a degree wheel accordingly he best method is to fit a fit a dial gauge to read off the valve collar, set to zero on the back of the cam and record the lift every 5 degrees of engine rotation.
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Paul Gasson
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Re: Valve timing checking

Post by Paul Gasson »

Keith, thank you. I think your information is from a Pitmans “Book of the Ariel” as I have now seen this elsewhere. Oddly, I have seen another copy, the tenth edition 1959, in which mentions 0.010” for SV engines and OHV, other than Red Hunters, which should be checked with 0.023-0.025”.
Roger, thanks also and I will try to follow your advice with the equipment I have to hand.
Charles, I appreciate all the details you have provided and will try to plot the lift as you have done. I am interested in the clearance you used to get close to the factory figures and will experiment with this.
David, noted your comments as well and will try to follow this. I’m not expecting to find exactly the factory figures but I am interested to see how close, or not my set up is. I also have two pinions to try, one is new old stock the other a new reproduction, the relationship between teeth and key slot appear to be different. Other than changing this, I do not know any other way to correct the timing if found to be a long way out. I will also use your clearance figure in addition to starting with 0.010 and 0.025 out of interest.
Whilst set up to do this work, I will try another set up with a single lobe cam and followers I think are HS specification that I own. I am not planning to use them, it’s just out of interest to compare with details in period publications and club resources.
Thanks all for your contribution I will post a follow up once I have some data.
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Re: Valve timing checking

Post by cmfalco »

Paul Gasson wrote: Mon May 29, 2023 1:17 pmI am interested in the clearance you used to get close to the factory figures and will experiment with this.
I set my indicator to 0 on the base circle of the cams and measured the lift at the top of the pushrods. The figures in my plots are of the actual measured lifts without any clearance. The arrows show the factory values, which my measurements would have come closest to had I used a clearance of 0.010"
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Re: Valve timing checking

Post by david.anderson »

Paul stated ‘Oddly, I have seen another copy, the tenth edition 1959, in which mentions 0.010” for SV engines and OHV, other than Red Hunters, which should be checked with 0.023-0.025”.’
The stated valve timing by Ariel for both red hunter twin lobe cams is .010”. See page 26 of the 1950 owners handbook regarding the 1950 red hunter cam. http://www.arielownersmcc.com/members_o ... ingles.pdf
The checking figure for the 1952 – 53 VH single lobe cam is also .010” but the checking figure for the June 53 and later single lobe cam is .023” inlet and .025”exhaust. see pages 20 – 25 of the 1952 -53 owners guide
http://www.arielownersmcc.com/members_o ... sGuide.pdf

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Re: Valve timing checking

Post by Paul Gasson »

I completed some checks today, note that my “workshop” is pretty basic, I do not have access to the measuring equipment and tools some Arielists do. The engine has a used and very slightly worn standard A7/642 twin lobe cam with probably the original cam gear which is in reasonable condition. The half time pinion is new old stock as are the cam followers. I checked the timing with different valve clearances and these are my results, I found it very difficult to be sure exactly when opening begins and ends, as has been mentioned, I checked each position several times and was getting a fairly consistent result.

Ariel figures 18 68 63 23
With 0.010” clearance 25 77 72 30 (correct checking clearance for this cam)
With 0.025” clearance 12 67 62 24
With 0.050” clearance 7 51 43 3 as suggested by David

I didn’t expect to get a match to published figures but would welcome any comments regarding my results. I didn’t get any further by changing the half time pinion, trying the single lobe cam I have or plotting the curves. I will probably go with what I have and maybe monitor wear and timing changes as the miles increase. It was interesting to do this as I’ve not tried this on an Ariel before.
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