commando camshafts

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acotrel

acotrel

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A question :
Is the standard 850 commando camshaft identical to the standard 750 (non-combat) commando camshaft ? The 750 combat camshaft appears to have an extra 26 degrees duration on both inlets and exhausts. The Haymes manual doesn't detail the 850 camshaft timings. When I built my 850 motor, I took a w or n 850 camshaft and a s ked the engineer t o give me his best Norton cam. The cam lobes were welded and reground. I thought I would probably get the combat grind, but the timings I achieved looked as thougft it was a standard 750 cam. I advanced it 15 dehrees from standard 750 timings to compensate for the two into one pipe. And I'm still wondering about what appears to be a big increase in torque. I've noticed that after I've increased the overall gearing, the bike staggers off in first gear, yet still comes up extreme ly quickly through the rev range. I feel that I need to satisfy myself that I am not imagining what is happening. I am not used to torquey fourstrokes, but I cannot believe that the guys who race regularly wouldn't use maxiuim gearing if the motor will pull it. I wonder if many have played with cam timing and gearing after they've fitted a two into one exhaust or simply stayed with the setup used for separate pipes ?
 
Just an opinion Alan, but it does sound like you have a standard commando profile, I reckon you need to try again with the cam, select which you want, PW3 would be a simple option and should work fine in your motor, not too highly priced and does not need radiused followers....though you might want the ones you have refaced....

'Staggering off the line' is how they feel to me with a close ratio 4 speed anyway, if that helps!
 
My problem is that the bike staggered off the start, with the old 4 speed CR box, then seems to come up to max revs with little effort. I feel there was no lag, where there should have been. With the new 6 speed box, I ordered first gear to be halfway between standard commando and manx ratios. (first gear in the old box was higher than manx ratio) I think I should have ordered it with a standard commando ratio first gear. I've always intended to increase the overall gearing, when I got the six speeder. I did that when I first fitted the 4 speed CR box, and the bike just went quicker, and was just as difficult to change before 7000 RPM limit was reached. I've been waiting for this motor to disintegrate, it revs to hard for it's own good. Our local circuit is very tight with three fairly long straights. The old 4 dspeed box was great, but I've always suspected it did not fully exploit the torque of the 850 commando motor. The high first gear always limitted what overall gearing I could use.
 
I did that when I first fitted the 4 speed CR box, and the bike just went quicker, and was just as difficult to change before 7000 RPM limit was reached. I've been waiting for this motor to disintegrate, it revs to hard for it's own good.
Click to expand...

Why does this make me smile ear-to-ear? :mrgreen:

Maybe some JS Motorsports components could give you a safety factor.
 
There is absolutely nothing wrong with the stock grind cam. It is well suited for the RPM range of a Norton longstroke motor. Many roadraces have been won with the stock grind cam.

I would be willing to bet that more performance cam installations end up loosing power under the curve than gain it. [power under the curve is what you want for roadrace or street- well maybe not at Daytona] Jim
 
Isnt the stock Commando grind the same as the famous 650ss cam?
Is was thought to be "the cam" back in the day. I know the 650ss got its head design from the Tom Phillis 500 Dommie that broke the ton at the TT, anyone know if the cam profile for the 650ss also came from that bike?

Reread a 1962 roadtest of the ss last night. Bruce Mainsmith got it up to a measured 119mph in heavy rain at the MIRA test track, quite an amazing machine in 1962.
 
A friend of mine had a featherbed manxman 650 years ago when we all had Triumphs. It was faster than a bonneville 650. I really like the idea of the longer carillo rods with the light hi-comp pistons. I played with Triumph 650s for years when I was a kid, riding on public roads, and always had full race motors. At one stage I bought two 350cc Gold Star BSA pisions, and reshaped the edge of the crown so it fitted up into the Triumph head. It was the best motor I ever built. In fact it was housed in an A10 BSA frame with unit Triumph fork yokes and handled perfectly. I should have raced that instead of buying the featherbed short stroke 500 I used for 12 years - wise in hindsight ?
These days I am retired and coming to the end of my superannuation. I made a decision and sold a very good TZ350G to buy the new gearbox. I will still find money to race somehow, but It will require a change of mindset, and a bit of application and exertion - and that won't be all bad. I find I can still ride a motor cycle, and I'm well past my crash and burn stage. The best race circuit is 11 kilometers from my home, and I can ride it almost without thinking because I rode there so often years ago. My bike self-steers , and really jumps away once it is rolling, so I'm avoiding our other local circuit which has a lot of variety. I believe the Seeley might still have a few tricks to try me out. For years I rode a bike which was a nasty peaky shit heap - if it dropped off the cam in a corner, and you slipped the clutch, it went instantly sideways. The Norton is so different - I love it ! When I raced as a kid, had a family, stressful job, studied, and never looked for a really good bike. I now know what I've been missing, Sad that I've found it so late in life, and there is really no class for it.
 
comnoz said:
There is absolutely nothing wrong with the stock grind cam. It is well suited for the RPM range of a Norton longstroke motor. Many roadraces have been won with the stock grind cam.

I would be willing to bet that more performance cam installations end up loosing power under the curve than gain it. [power under the curve is what you want for roadrace or street- well maybe not at Daytona] Jim
Click to expand...


Likable quote.
 
I would definitely go for the road 1st gear, you can get off the line so much quicker and once you're rolling there's no problem if there's a slight gap between 1st and 2nd. I have a road four speed and a quaife 5 speed with their "road 1st" and it's a lot harder to get a good start with the quaife.
With our short races of just a handful of laps a good start is crucial.

I have never heard of advancing a cam by as much as 15 degrees to account for a 2:1 exhaust. It seems a lot. Mind you, I have never had much success with 2:1 so I use 2:2 on mine.
 
worntorn said:
Isnt the stock Commando grind the same as the famous 650ss cam?
Is was thought to be "the cam" back in the day. I know the 650ss got its head design from the Tom Phillis 500 Dommie that broke the ton at the TT, anyone know if the cam profile for the 650ss also came from that bike?
Click to expand...

Yes the stock Commando grind is the same as the 650SS cam and no this cam profile did not come from the Lowboy Domiracer.
If you are interested I can provide you with the Domiracer cam data (have to look it up).
 
" If you are interested I can provide you with the Domiracer cam data (have to look it up). "

By all means ; go ahead :

Acotrel , with my limited experiance on the Norton ( 10.000 miles ) and minamal fidling . I think the 2 - 1 bias is midrange and Less Weight , & flexability .
9 was disapointed the 2-1 lost top end . ON 2S cam , seemed ok on S . :? )
The thing was crankeyer with the Dual Interstate headers , but but envigorateing . The OVERLAP period ( I & E open simultaeneous ) is I think EASIEST and
most obvious way to see if Cam timings ' about right ' . Id settled for 5 Deg. advanced on a 2S Combat Camshaft .

Running say 7/8 throttle , and letting Revs Climb , throttle set , The 2S starts doing things around 3.500 and at 4.000 is somewhat more stropy than below 3.

The ' Standard ' Comando S cam , useing a 2 - 1 and big mega , ran seamlessly from 1.000 to past 7.000 .
7/8 Thottle test will estabish powerband characteristics.

Std would pull from 800 , 2S from 1100 ( non snatch speed ) another indicator .

Apparently Williams considered 7.200 Max. for Longstroke .Though decent valve gear ( Domiracer 500 ) aledgedly ran to 8 / 8.500 ,
Dunstall and other have used 7.500 . The Old RACE MOTOR , though incresed service ( wear ) rates intrude on longivity .

With modern metalury / precission machineing , the 7.500 should be o.k. for a ' desperate ' if a whizz bang is trying to sneak through .

Incedently , NORTON rated the 750 Short Stroke at 8.000 back in 74 or whenever it was . The inside of this head would be a 850 long stroke Norvil ??? . :mrgreen:
 
Here you are:
Lowboy 500 works Domiracer 1961 cam: int.open 70 btc, int.close 77 abc, exh.open 73 bbc, exh.close 54 atc, intake lob centre 93,5 degree, max.camlift: int.9,4mm exh.8,2mm Closest to these figures are the Dunstall racing cams (after Norton quit the Lowboy project P.D. bought all the works racing remains).
 
Thanks for that . reading a Mag. from the time, he was invited to ' Clear it out ' . Thought he had a van or twos parts .Seven Van Loads later . . . .
Anything Left was to go to ' scrap ' . Bargain of the centurie , And a dead halt for the factory as to development resources there until Norvil surfaces .

Figures give about Eight Degrees ' Lead ' . :|
 
nortonspeed said:
worntorn said:
Isnt the stock Commando grind the same as the famous 650ss cam?
Is was thought to be "the cam" back in the day. I know the 650ss got its head design from the Tom Phillis 500 Dommie that broke the ton at the TT, anyone know if the cam profile for the 650ss also came from that bike?
Click to expand...

Yes the stock Commando grind is the same as the 650SS cam and no this cam profile did not come from the Lowboy Domiracer.
If you are interested I can provide you with the Domiracer cam data (have to look it up).
Click to expand...


The works Lowboy 500 Domiracer had a full race cam, that would have been unsuitable for road use as it was strictly for track use. (It had a ½ inch lift, amongst other, extreme valve timing.)
To anyone out there, avoid buying a Dunstall full race cam unseen, some of them were made by grinding flats every 5 degrees –don’t ask me how I know :!:
 
comnoz said:
There is absolutely nothing wrong with the stock grind cam. It is well suited for the RPM range of a Norton longstroke motor. Many roadraces have been won with the stock grind cam.

I would be willing to bet that more performance cam installations end up loosing power under the curve than gain it. [power under the curve is what you want for roadrace or street- well maybe not at Daytona] Jim
Click to expand...


JIm, I was not criticising the stock cam, I rode a season using one, in a stock 750 fastback and I reckon it was a good start package. My logical progression to an ex Thruxton cam came with the package I bought. More recently I have ridden with a PW cam and liked that an dthink it was balanced to rest of the engine too.

Could not agree more that cam alone does not give the return some expect but surely at some stage you need to move it on? When do you feel that comes?
 
SteveA said:
comnoz said:
There is absolutely nothing wrong with the stock grind cam. It is well suited for the RPM range of a Norton longstroke motor. Many roadraces have been won with the stock grind cam.

I would be willing to bet that more performance cam installations end up loosing power under the curve than gain it. [power under the curve is what you want for roadrace or street- well maybe not at Daytona] Jim
Click to expand...


JIm, I was not criticising the stock cam, I rode a season using one, in a stock 750 fastback and I reckon it was a good start package. My logical progression to an ex Thruxton cam came with the package I bought. More recently I have ridden with a PW cam and liked that an dthink it was balanced to rest of the engine too.

Could not agree more that cam alone does not give the return some expect but surely at some stage you need to move it on? When do you feel that comes?
Click to expand...

The first consideration in going to a cam with more timing is the fact that it will narrow the powerband. You can certainly make more power with a race cam in a narrow RPM range but to take advantage of the power you will need closer transmission ratios. You also have to consider how a narrower powerband is going to affect your launch if you have a tall first gear.

You will also need a considerable increase in compression ratio to go with the PW3 cam.

If you have those two covered you would be in good shape but you may be better off to spend the money on the head instead of the cam and gearbox. A bit of port work with oversized intake valves will net a larger power gain without narrowing the powerband. Jim
 
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