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N15cs camshaft


Just putting a N15 (Atlas) engine together - it was in bits when I got it - just noticed the camshaft timing side has 3 woodruff key slots in it spaced at 120 deg? I thought Norton cams had single key slot.

It looks like a Norton camshaft, the drive side fits and it has the two chamfered slots for the breather disc. 

Is this correct for this bike?



Sounds like an aftermarket cam ,possibly a Dunstall or Norris . If you measure the timings and lift accurately someone will be able to ID it for you.   This will then enable you to accurately set it up for best performance and  running clearances (which could well be different to the standard settings.


Sounds like a Somerton Cam as sold by many tuning shops ( like Dunstall ) in the sixties and seventies.  It may need radiussed followers if it's a sporty one.  Measure the base circle diameter and subtract it from the total lift for the inlet and exhaust.  That should give a better clue.  Some of the US offerings also had three keyways.  Good luck, Howard 


Thanks, the bike came form America so it must be a US camshaft, I compared it to a Commando camshaft and the cam lobe is much flatter. I am not sure what this means but if it worked before I guess it will work again! Thanks for your help. Steve


Hello again Steve - flat lobes usually means that the valves will open and close quicker and the valves will obviously be open for longer.  You'll have to look at the valve timing figures when you get round to it,  unless you already marked the keyway that was used before.  There is a lot information about the heavyweight twin camshafts and valve timing figures on Dyno-Dave's  Technical Services  ( website and it's free to view.  Regards, Howard


The camshaft that was used in all the N15CS, G15CS, and the P11 series of bikes was the standard 650ss, camshaft. There were so many American companies that made camshafts for UK built bikes, and Megacycle must have bought most or all these companies profiles. Norris also supplied Titanium valve spring coller's, as well as special valve springs to go with the camshafts. I have one of their camshafts, as well, as the springs and those Titanium valve spring coller's. The Norris valve springs also had a damper spring included in their valve springs. 


I am not an owner of any hybrids however , I have over some period been forced to look at some issues. The details will seem to nit pick but I'll offer it up anyway.

An N15 is a not a full 20/atlas. The main difference for not being an interchange is the bolt up to the primary which is closer to the flat commando. The Atlas had a dual level surface for the sheetmetal primary. I separate and segregate my 20/atlas engines from commando engines.

Since 1988 I may have bought $15,000 of british parts including a half dozen cams. I only bought 1 american sourced cam and it was for another friends engine.

All this era NHT used the 22729 (SS) cam which was a flat lifter cam with outboard tach drive. Only under extremely skilled race engine building would I consider an aftermarket race cam with radiused lifters.  For a street use bike, I'd suggest you stay with a good SS cam to improve longevity.

If anything is incorrect, feel free to correct me.


On the topic of flat or radiused followers. As Phil Vincent writes in "Tuning for Speed" , the radius of the follower doesn't affect lift or valve timing, but flat followers accelerate the valve opening and increase valve opening somewhat.  They perhaps used radiused followers on the early engines to reduce valve acceleration and improve the life of the cams? Then as the motorcycle magazines started emphasising performance figures and bikes moved further towards leisure toys they were forced to "tune up" the engines (giving the public the SS models) regardless of any adverse effects on cam life?


"flat followers accelerate the valve opening and increase valve opening somewhat."

True but reduces manufacturing cost I would guess significantly as well as reconditioning costs. I should rephrase...radius and flat have identical full lift as can be seen below


Thanks David. I wonder why they bothered to radius them, since the areas under the curves are so close? Anyway...sometimes owners have asked which type they should have, and it looks as if it really doesn't matter (use whatever you have or can get hold of)?


...for the link to camsurvey.

It has helped me with my problem of the noisy engine - now I know my cam is correct.

It has an almost identical curve to the cam140 which is the standard Dommi 88 cam.



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