4s cam timing and torquiest cam.

I have a Norvil 4s cam, which I didn't time up on installation two years ago. I have checked the timing today and it is showing 150 thou lift at TDC. Does anybody know what it should be or if this is correct?

I have been slightly disappointed with the engine characteristics with this cam, as the engine seems to be fairly flat until it gets to nearly 5,000 rpm when the engine note changes and it pulls reasonably well. I am addressing the out of true intake manifolds problem, so possibly this will help things, also I'm going to make sure that the ignition timing marks are accurate on the timing plate, which I have not yet done. I will be interested to find out if the cam is very far out, as obviously this might be a lot of the problem.

I knew that the 4s would move the torque/ power up the rev range, but I don't remember it being as extremre as it is on my current Norton. Maybe having it at 920cc before masked the symptoms? So I am considering going back to the standard camshaft, for the low end torque.......another dilemma!

Hi Reggie,
If you measure on the follower/pushrod, then you should have 188.5 thou lift @TDC. If I rememebr properly timing figures were 65/83/88/60.

also for better top end the tappets should be set at 16thou which is what the ramps were designed for. Some run them at 8/10thou which is ok, but you lose the extra top end, but for the road thats not really relevant if you want to keep plod off your tail

hi reggie according to norvil it should be set to 0.212 thou on inlet valve top collars @tdc using 0.016 valve clearance,as seeley says degree figures are 65 83 inlet 88 60 exhaust ,best performance is with 16 thou clearance.another way is lobe centers inlet is 99degrees atdc exhaust is 104 degrees btdc ,best way is to concentrate on inlets as the exhaust follow suit , must say i never noticed a step in power on my 750 it just pulled like a train from nothing till it ran out of puff at about 7000 revs hope this helps keep us informed chris

It may not be (entirely) the cam.

Thanks for the information.

Seely wrote;

If you measure on the follower/pushrod, then you should have 188.5 thou lift @TDC.

Click to expand...

chris wrote;

should be set to 0.212 thou on inlet valve top collars @tdc using 0.016 valve clearance

Click to expand...

The difference of 23.5 thou by measuring using the different locations is more than the obvious 16 thou tappet clearance. Is this due to the valve geometery?

Hi Reggie,

Yes, this is due to the rocker ratio of 1.13 :1

If you multiply .1885 by 1.13 you will get .213....it's due to the uneven lengths of the rocker arms on either side of the spindle.

Cheers

John

I thought it must be. Thanks for the equation John.

To get 1885 thou at TDC I'm having to advance the crank approx 10 degrees past TDC.

I assume this will be equal to 5 degrees cam advance as the cam runs at half speed :?: I'll find out by testing. I have a chart of the combinations to advance/retard the cam by 5 degree increments.

I must be going into "garden shed nerd mode," as I'm quite enjoying doing this :shock:

Hi Reggie, yes it can be "fun"

I used to use a vernier cam sprocket, but now I get my cams from a different supplier and can set them up on standard marks and know that it's right!

Could I enquire if that might be Steve Maney?

Actually, no! I have a few motors with different cams....PW3 seem to be spot on straight out of the box, and I get my own cams made locally by David Newman

John, do you use the PW3 for racing or road use? There seems to be a general concensus of opinion that as Peter Williams designed it, and Mick Hemmings has had success with it, that it was the epitomy of Norton twin camshaft design.

I just wondered what you thought about its characteristics. Would you recommend it for "brisk" road use i.e. has it a good spread of torque, or does it deliver power high up the revs? I realise that this is subjective to the general state of tune of the motor.

Hope you don't mind me asking a subjective question.

Cam timing data, 1/2-way down the page: http://victorylibrary.com/brit/norton.htm

Hi Reggie,
The PW3 gives a very broad spread of power and would be ideal for brisk road use. One of the first people I know who used one on the road was Geoff at Russell Motors in London, and he used it in his caf racer. He said he couldn't believe how torquey the motor was. You could always give him a ring for direct feedback on that one!

They're also designed with Norton engine characteristics in mind, and aren't hard on the valve gear either, so it would probably be better for a road motor than the 4S which needs a few revs to really get going! Don't forget the design of the PW3 is about 20 years newer than the 4S, so a lot was learned in that time!

Hope this helps

John

Hi Seeley, you are wrong there as the PW3 cam (10,7mm valve lift intake/exhaust) is harder on the valve gear then the 4S cam (10,5mm intake and 9,4mm exhaust). Also the PW3 cam hardness has been tested only 27 rockwell and the 4S cam did 60 rockwell (tested by Dyno Dave Comeau Atlantic Green technical services).
I tried lots of cams (dunstall, somerton, norton, megacycle etc) for racing and road all with their specified purpose.
For road use I suggest the Megacycle (excellent quality) 560-NR cam (strong low and mid-range powerband and easier on the valve gear, 10mm valve lift int/exh. compared to the PW3)
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Don't forget, actual lift is not as important as HOW it is lifted! Fiercer opening ramps are harder on the valve train no mater what the lift is. Also I've been using my PW3 since 1992 and it's still as good as new. Chilled iron was the recommended material for commando cams as it tends to last longer....I had 4S cams that only lasted a season. I've seen a Megacycle once....very few people over here use them!!

Seeley I agree, fierce opening ramps are hard on the valve train as well.
But Norton cams with approximately the same lift don't differ that much (once had a Somerton cam with comparative fierce opening ramp). I always messure the valvespringpressure because each set (of various manufacturers) can differ a lot! So actual lift and joined springpressure is what we have to look after to ease the valve train on our Nortons I guess.

Thats true, but you can also run a PW3 with standard valve springs....not quite so easy with a 4S The PW3 only has 145 thou lift at TDC compared to 188 on the 4S, so the initial opening isn't as fierce. I'd worry more about seat pressure than the load when the valve is open though.

The PW3, whether the hardness is greater or less than other ones, tends to wear less than other ones I've tried, although my own cams that I have made are also made of chilled iron and they don't seem to wear either...maybe it's because I use R40??

I've also seen Somertons (for a triumph) talk about a brick on a stick!!!

Interesting to know your opinion of the PW3. Thanks John.
Panic, thanks for the link for the cam timing.

The PW3 only has 145 thou lift at TDC compared to 188 on the 4S

Comparos between cams as to lift rate aren't valid unless the duration is very close (and specifically, the intake opening point BTDC is very close).
Yes, a higher lift can have a slower (safer) lift rate if the duration is long enough. Frequently cams made for road racing compromise lift (even though it does reduce power somewhat) to permit lower spring tension and greater life expectancy.
Some very modern cams are also made with asymmetrical lobes that have higher acceleration on opening than closing, so even a comparison of lift and duration won't be definitive as to the relative rates.
Spring tension is also a big variable. The change in weight vs. change in maximum safe RPM is fairly linear (if all components are weighed, same cam), but a change in RPM varies as the square of spring tension. E.g. if you need 200 lbs. open tension for 7,000 RPM, going up to 7,500 requires 230 lbs. (7,500^2 ÷ 7,000^2 = 14.8% more) tension rather than the linear 214 lbs. (7,500 ÷ 7,000 = 7.1% more).
There have also been comments posted (elsewhere) that "valve train weight on the pushrod side has no effect on speed". This has been repeated so many times that it begins to acquire the patina of wisdom, but it has no basis.
A high-ratio BBC engine with 1.73:1 ratio will have only minor benefit from weight savings on the pushrod side, but a small-ratio engine (Norton, Triumph twins, Gold Star) is much more affected.
The math: the proportion of weight effect varies as the rocker ratio squared.
An engine with 1.13:1 rockers has 78.3% (1 ÷ 1.13^2) effect for changes in pushrod, tappet and short-side rocker lever weight vs. changes in valve, spring, adjuster, collar and long-side rocker lever weight.

While some cam manufacturers recommend radiused lifters to ease the valve ramp has anyone ever tried reverse radiused grinds on the lifters? It might be useful to have a set of 1', 2', and 3' radiuses to experiment with. Of coarse once you have arrived at the optimum for your application you could simply compute those specs into your next cam grind.