Norris N750R cam specs

Interbak · Jun 30, 2021

I’m digging back into an old project that’s been stalled for years. The engine came to me with a Norris N750R cam installed, and that’s what was used when it was rebuilt back in the early 90’s. Does anyone have the specs for this cam, particularly the proper valve clearance? I had a spec sheet for it back when this project was started, but after multiple house moves and other projects it has disappeare.

thanks B

kommando · Jun 30, 2021

Megacycle took over Norris cams, assuming the Mega 560-NR is the Norris 750R then

Partial info

Norton twin camsurvey

and a bit more

Old Britts, Norton Cams

ILLF8ED · Jun 30, 2021

Norris R or RX. I have this spec sheet for RX.

ILLF8ED · Jun 30, 2021

Norris RX profile online provided by David Comeau on atlanticgreen.

http://atlanticgreen.com/images/cam510.gif

Interbak · Jun 30, 2021

Thanks guys,

acotrel · Jun 30, 2021

Interbak said:
I’m digging back into an old project that’s been stalled for years. The engine came to me with a Norris N750R cam installed, and that’s what was used when it was rebuilt back in the early 90’s. Does anyone have the specs for this cam, particularly the proper valve clearance? I had a spec sheet for it back when this project was started, but after multiple house moves and other projects it has disappeare.

thanks B

How do you think the first guy to ever fit a cam into a Commando engine determined what the tappet clearance should be ? - If you set it to 2 and 4 thou, then put a degree disc on the motor, you will get it right if you look at the timings page in 'Tuning for speed'. Within limits, it does not matter much if you are out by a couple of degrees. Very few people ever adjust valve timing to suit their exhaust system. If you race, you might move the cam backwards and forwards to find the best position. The Norris spec. sheet might have been developed that way, but you would need to know the exhaust system configuration which suits the cam.
The tappet clearance is probably more about motor expansion than valve timing.

lcrken · Jul 1, 2021

Norris 1976 catalog specs for Norton cams, including N750R:

Unfortunately, the catalog does not list recommended valve clearances, nor does it list the checking clearances for measuring duration. The lift values are at the valve, not the cam.

Recommended valve clearances for the Norris cams I've seen range from .008"/.010" for the SS, SSS, and N480 cams to .015"/.015" for the N750D and D+ cams.

Ken

Seeley920 · Jul 1, 2021

I have a copy of the timing sheet from Norris, but it's in storage at the moment. I'll be able to get to it in about 2 weeks (if I can find it)

acotrel · Jul 1, 2021

Whatever the tappet clearances are which are specified for a normal Commando can, are probably correct for any cam. They should be checked when the motor is hot. The tappet clearances are used to compensate for expansion of motor components due to heat. I don't use feeler gauges, the threads on the tappet adjusters are 26 TPI. So one complete turn ofthe adjuster screw is about one 25th of an inch - 40 thou ? Often there is a dimple on the end of the valve stem where the adjuster impacts. It stops feeler gauges from accurately measuring the correct clearance. With any cam, you need to get the timings right. If I find an an error, I usually split the difference and alter both the valve opening and closing points.

acotrel · Jul 1, 2021

With my 850 motor, because I use methanol fuel, the motor never gets hot enough to lose power. I use tappet clearances of 2 and 4 thou of an inch. With petrol as fuel, you would need more.

ILLF8ED · Jul 1, 2021

lcrken said:
Norris 1976 catalog specs for Norton cams, including N750R:

View attachment 80837

Unfortunately, the catalog does not list recommended valve clearances, nor does it list the checking clearances for measuring duration. The lift values are at the valve, not the cam.

Recommended valve clearances for the Norris cams I've seen range from .008"/.010" for the SS, SSS, and N480 cams to .015"/.015" for the N750D and D+ cams.

Ken

The N750R has the same lift and duration as the spec sheet above. If it is a camshaft made by Norris the tappet clearance should work.

Fast Eddie · Jul 1, 2021

acotrel said:
Whatever the tappet clearances are which are specified for a normal Commando can, are probably correct for any cam.

I think that’s quite wrong.

Seeley920 · Jul 2, 2021

Fast Eddie said:
I think that’s quite wrong.

Nigel is correct, it has nothing to do with methanol. You can set you tappets to no clearance if your bike is just sitting in the shed

Tappet clearances are specified to take the opening ramps into account and can make a difference to performance. E.G a 4S cam is specified at .016". That is because of the opening ramp. Some people run them at a slightly tighter clearance on the road to soften the power (or on a tight circuit like Lydden for a bit more mid range) but it gives best power when set to .016"

Norris N750R cam specs

Interbak

kommando

ILLF8ED

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