4 S Cam
- Thread starter pierodn
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Piero
All you need to know, is in this article.
http://www.nortonownersclub.org/support/technical-support-commando/camshafts
Peter
All you need to know, is in this article.
http://www.nortonownersclub.org/support/technical-support-commando/camshafts
Peter
pierodn said:
Without reading the article, the short answer if you put it in a standard engine is probably not much.
It was explained at the time it needed to be installed in conjunction with all the other hop-up tricks, to get the most from it.
Nortons put out Tuning Sheets No 1 and No 2 to got with it, for owners to get the maximum benefit.
It was said the Dennis Poore wanted to sell an 850 Combat model - but noise regulations wouldn't let them.
So they produced the 4S cam, and the Tuning Sheets to let owners build their own.
Upping the compression is a big part of this, a low compression motor just isn't in the game...
P.S. The 4S cam was in the 850 Mk1 850 that the factory built that recorded an average 143 mph over the flying km at Elvington airfield speed meet in 1973.
The factory guys that built that bike developed the 4S cam for it....
Piero, I always put 4S cams in my 750 engines whenever I do a rebuild, they work better than standard in the midrange and top end, but really go well if you skim the head a bit to boost the compression. You can get a standard cam reground to any specification you like by RGM Motors and it is much cheaper than buying a new camshaft.
dave M said:
Hi,
I have a 750 combat head and a 4s cam from different engines!
I would mount the Cobat head, which has a flat base, with three seals to lower compression.
Can I mount the 4 S cam too?.
I read that the 4s cam operates best with ported 34 mm carbs and big valve head, the Exhaust timings are the same, inlet on the 4 s opens 6 degrees earlier than the 2 's.
What does it mean?
I have to change the advance??
Thanks.
Piero
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The machining of the cams takes care of the advance so you install to the timing marks but double check the actual timing of the valves for a 4S cam and adjust if required.
These cams work best with high compression so reconsider your plan to decompress your Combat.
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Interesting article from the NOC. Seems that my intention to advance the combat 2S cam by 6 degrees was not all silly. Ass beats class ?
My question is - if advancing the 2S cam that much gives increased midrange, why aren't they fitted with that advance as standard ? Another Norton detuning trick, like changing the steering geometry to make the bike safer ?
My question is - if advancing the 2S cam that much gives increased midrange, why aren't they fitted with that advance as standard ? Another Norton detuning trick, like changing the steering geometry to make the bike safer ?
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You fit the cam using the factory manual instructions, ie using the woodruff key to engage with the timing gear and with the right number of chain links again as per the factory manual instructions, you then set the camchain tension as per the manual.
You then check the lift figures for the cam match the listed figures using a Dial indicator to show lift and a degree wheel on the crank.
Piero,
There are two different timing aspects, these are 'cam-timing' which refers to the relationship of the cam shaft to the crank shaft and as Kommando says this is done as per a normal cam shaft of counting the appropriate number of chain links between the two timing sprockets, the actuall valve opening positions can be checked for accuracy with a degree wheel and a dial guage, or just set it and leave it since unless you have a vernier cam sprocket there is no way to fine tune this.
There is also 'ignition timing' which is the relationship of the spark plug timing to crank shaft rotation, the ignition timing should be set at the same position as standard unless otherwise stated.
There are two different timing aspects, these are 'cam-timing' which refers to the relationship of the cam shaft to the crank shaft and as Kommando says this is done as per a normal cam shaft of counting the appropriate number of chain links between the two timing sprockets, the actuall valve opening positions can be checked for accuracy with a degree wheel and a dial guage, or just set it and leave it since unless you have a vernier cam sprocket there is no way to fine tune this.
There is also 'ignition timing' which is the relationship of the spark plug timing to crank shaft rotation, the ignition timing should be set at the same position as standard unless otherwise stated.
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For cam timing, I suggest that inlet opening at about 65 degrees BTDC is good as long the exhaust opening does not then happen much before 90 degrees before BBDC. If the exhaust opens too early, the bike will be loud and develop less power unless your exhaust system presents substantial back pressure. The cam closing points are much less important. If you broach two more keyways at random into the cam sprocket, life will be easier.
For ignition timing, if you are running your bike on petrol, stick with the manufacturer's specification and tune your carburettors to it.
For ignition timing, if you are running your bike on petrol, stick with the manufacturer's specification and tune your carburettors to it.
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pierodn
check here and read.
http://victorylibrary.com/brit/norton-c.htm
scroll down to Cam Timing Adjustment in Small Increments
Cheers,
Thomas
CNN
check here and read.
http://victorylibrary.com/brit/norton-c.htm
scroll down to Cam Timing Adjustment in Small Increments
Cheers,
Thomas
CNN
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