High Noccers.
I have recently found out that my Dome 99 is fitted with a camshaft marked T221903 and X2 on its body. From what it says in Roy Bacons book on Norton Twin Restoration, X2 signifies that it is a 650 camshaft. Does this mean that I shouldchange the rocker clearance from 0.003'' inlet and 0.005'' exhaust to 0.006'' and 0.008'' respectively? Or are there other factors that I need to take in to account?
I believe that somewhere I read that the X2 symbol was, in fact,an indication to the degree of surface hardness of the camshaft! Could some erudite club member enlighten me?
Peter M.
I think you have a 650 cam…
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This is most likely to be…
This is most likely to be a Dominator SS camshaft as fitted to all the big twins after 1960. The valve timing, of this camshaft, can possibly cause an issue with earlier engine unless the clearances are set to 6 & 8 thou. ie you might get valve heads touching the piston tops or other valves.
A little more info may help with the Technical issues. What year is your Norton? Is the engine standard for that year or are there any other modifications?
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Previously phil_hannam wro…
Previously phil_hannam wrote:
This is most likely to be a Dominator SS camshaft as fitted to all the big twins after 1960. The valve timing, of this camshaft, can possibly cause an issue with earlier engine unless the clearances are set to 6 & 8 thou. ie you might get valve heads touching the piston tops or other valves.
A little more info may help with the Technical issues. What year is your Norton? Is the engine standard for that year or are there any other modifications?
Thanks guys for your post. The engine is from a 1960 delux 99. I have been running it with 0.003/0.005'' rocker clearance with no problem. I don't thrash the engine; usually cruising at 60 mph on quarter throttle, so itdoes not get excessively hot. Maybe that'swhygoing for a larger gap wasn't necessary. Some time in the past someone has bored out the top of the pushrod tunnels like Robert suggested.
I've tried to measure the valve timing with the head off and using a dial gauge directly on the top of the pushrods.
Inlet pushrod started to open [0.005'' lift ] at 90 BTDC, reaches0.115'' at TDC, maximum lift was 0.32'' at 80 ATDC and closed at 75 BTDC.
The exhaust pushrod figures were; open 79ATDC, peaks [0.32''] 70 ABDC, closes50 ATDC.
Am I right in thinking that, with the head on, I should check the valve timing with the rocker clearance set to0.016'' and use a 0.003 feeler gauge to determine when thegap is opening and closing using an [RGM] enginetiming disc? Is the0.016'' to allow for the quieting ramp?
Thanks for the help,
Peter M.
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Attachment may be of some…
Attachment may be of some use. It is from an old John Hudson article and mostly deals with Commando camshafts but there are references and data relevant to some Dommie engines.
Attachments
camshaft-data-jpg
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Looks like the ramps are t…
Looks like the ramps are the same for both cams,although JH told me to use 16 thou clearance with a 3 thou feeler for the SS cam ,Your figures will not be the same doing it from the pushrod.I would try it with 6and 8 thou running ,if no performance benefit and noisy go back to 3 and 5 or hedge bets with 4 and 6!.
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I think you have a 650 cam,others here will know for sure. I fitted one to my old 88 and changed nothing else,did not have any problems.Some may say you should uprate the push rods ,make more clearance in the barrel tunnels etc, and if you are going to rev it like a loon then they are right,but who does?, with 55 year old rods?.The Cam timing figures are different and its worth checking these for the best result.I think the larger clearances are to allow for hotter running, some cam designs do need larger clearances to get the correct timing .