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Aug 17, 2006
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I was going to jump in on the recent post about cams but it turm into a thread about oil etc
My question is how do different cams compare, I read about lift and duration of 2s 3s 4s 7s etc but how does this effect the performance and feel of the engine ?
I require a cam for my 850 roadster fitted with standard head, valves. carbs , k+n air filter peashooter exhausts.
the bike has standard footrests and quite high wide bars so high speed
flat out riding is not what I am looking for , top gear flexibility and mid range roll on power is my aim. In the future I may look to run a single carb and 920cc kit
comments and recommendations welcome
does any one have any Dyno comparison graphs ?
thanks Barry
The cam is were everything starts as far as the rest of the components are concerned. Your instincts are right on. There are infinite possibilities as to Dyno results with the different cams Some bikes can't even get their valves to follow the profile ground because of component selection.
Many folks like you as far as needs are out there , torquer cams being the watch word. (Since my bike can be beaten by any good modern out there in the top end department I just want it to do what it did well from the factory.)
So more low down torque and a nice wide band right up to say 6000 RPM. At that point I don't care if it fails on it's face.
Now you already own a bit of a hot rod of it's day and a stock cam with good component selection, could go a long way to giving you what you need. If you find an honest cam person they will tell you that the production cams were not all that well ground, not all that accurate, the timing of that cam was a bit hit and miss what with chain adjustment and key way cutting. If I were starting all over again with a engine build with these basic ideas in mind the 2S or the PW3 cams with lots of attention to automatic cam tensioner ,vernier cam sprocket, the best read stiffest push rods,strong but not too strong valve springs, a great Pazon Smart Fire ignition timed to a corrected 31 degrees BTDC, some porting by Jim Comstock for a flatter floor in the intake and exhaust ports. I would be aiming at 50 lbs torque @3000 RPM and 60 HP@ 5500.
There are many other toys to choose from Exhaust systems, carbs, but it all starts right at the cam and branches out from there. Keep in mind that it all has to run on fuels that are changing everyday to meet emissions rules and the hotter you build it the narrower your ability to adjust to future changes.
The cam dilemma has caused me a significant amount of concern also and after a lot of thought I came to the same conclusion as Norbsa; the stock cam should be the choice unless one is modifying the engine for performance above the factory spec. My main concern however still relates to the accuracy of the grind on the stock cam. I understand the stock cams were not ground to a high level of accuracy and even if the grind is mild it would be a great help to have the timing spot on.

So,, has anyone degreed the stock cams to see just how far out they are and has anyone ever had a stock cam blueprinted to get it right?

Final question: what is involved in fitting needle bearings instead of the bushes?

Thanks Mates :D

The process of fitting needle roller bearings would largely depend on the respective heat treatment / hardness of each individual cam.

The probable reason bushes are used instead of bearings is that the bushes will wear instead of the cam therefore being inexpensively and easily replaced, on the other hand if you fit needle rollers the cam journals will wear instead of the hardened needle rollers, making the whole process an expensive disaster.

Hi Mike, You may have misunderstood the reason for the conversion...
So yes you must have your cam up to 60-65 or even harder on Rockwell C scale to do this, the reason for the hassle is a quick change cam. By building a cartridge that holds the timing side bearing for the cam, a hole large enough to pull the lobes through is gained. Adding an end feed high pressure oil feed to the cam on the drive side would also be done at this time. If your racing, the need to check and or change the cam makes all this worth the time. Most of the people doing this would also machine some threaded plugs into the rocker boxes so that the push rods can be removed and replaced without taking off the head. Same thing speed in getting a fix done in between races.
Paul Dunstall used to convert to needle races but did not have the quick change feature. He added a pressure fed oil supply from the rocker shaft feed.
If Sam is interested in power curves check out the 1974 Cycle test on an 850 JPN (at the rear wheel) I have these compared with a 750 done by Classic Bike Feb 05. Different engine sizes and 31 yrs between Dyno designs! You can use the points for the Combat (2S) from the workshop manual (49ft/bs @ 6000, and 52.6ft/lbs @ 6500 (65HP)) but that leaves big gaps.
If you want to maintain low end torque then I'd say anything other than std will not provide this. One thing that will is a good head job as Norbsa advised. Try Cylinder Head Shop, now in Ireland, he's very slow but his valve work and porting is well known. I had mine done last Feb and was well pleased.
pommie john said:
I'd be very interested to see the power curves from a 750 and 850.
Where can I see them?

There is a comparison chart showing the BHP/torque differences between the standard 750/ 750 Combat/ 850 models included in Mick Duckworth's 'Norton Commando' book.
L.A.B. said:
There is a comparison chart showing the BHP/torque differences between the standard 750/ 750 Combat/ 850 models included in Mick Duckworth's 'Norton Commando' book.

Are they rear wheel figures, by which I mean real dyno graphs, not quoted figures from Norton?
pommie john said:
Are they rear wheel figures, by which I mean real dyno graphs, not quoted figures from Norton?

The book doesn't actually say;-although the output figures shown on the graph appear to be consistently lower than the manufacturer's *quoted* figures!
I haven't got a copy of that book. I'll have a look for it.
Do you know of any dyno charts I can see online? I've just had mine on the dyno and would like something to compare it to.
pommie john

If you email me (you don't show an email contact, only PM) I will scan the graph and send it to you.
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