Norris RX camshaft update

I use the long velocity stacks on my Mk2 Amals, however I don't believe they are critical to the performance, just better. You should s till be able to feel the power band that a race can gives even without them.
I found this article by Kenny Cummins interesting - all easy stuff ! :

http://seeleynorton.com/technical/motor ... ansmission

Re-ckecked the max lift of the intake and measured 76degrees BBDC. My calculation for correct max lift is spec 54degrees BTDC open and 82degrees ABDC close. Half way is 76degrees BBDC. So unless I've made an error calculating the cam timing is spot on. Took the 750 out for the acid test yesterday going over Vasco road pass into a roughly 50mph wind. It could not hold 60mph going up the hill. Another idea came to mind today, though. I have an XS650 reed valve in the engine breather line. What if this reed valve is plugged to some degree? Will have to check that when I get some time. I know typically there is a while emulsion of moisture and oil that goes up the breather pipe. What made me think of this is recently the tach drive that has an oil seal modification started leaking pretty bad. All of this concern is that I really don't want to have to open the engine again and replace the camshaft if I can get this Norris RX to work.

What I am not willing to do is modify the intake (longer tract) as I want to use the stock manifolds, carbs and air clear. The stock set up fits so well. The exhaust tract couldn't be more open without just removing the mufflers, so no changes there either.

I don't use max lift to set cam timing , although I feel that I should. I've always worked with the opening and closing points with the tappets set to run clearance . I think you need to use the degree disc and find out where those points are then compare them with the timings given for single cylinder 350cc racing motors in tuning for speed. What you are effectively doing is setting up the motor to establish similar standing waves in the exhaust and inlet tracts, so the timings are comparable for similar rev ranges, regardless of stroke length. If you use a two into one exhaust, the timings will need to be substantially different.
If the cam supplier has recommended timings, use those as a starting point then keep track of performance changes as you adjust the timing. - Difficult to do if you can only change it by one tooth on the sprocket at a time. Just remember one thing - YOU are in control.

Have you tried larger main jets? Sluggish top end indicates main jets are too small.

acotrel said:

I don't use max lift to set cam timing , although I feel that I should. I've always worked with the opening and closing points with the tappets set to run clearance . I think you need to use the degree disc and find out where those points are then compare them with the timings given for single cylinder 350cc racing motors in tuning for speed. What you are effectively doing is setting up the motor to establish similar standing waves in the exhaust and inlet tracts, so the timings are comparable for similar rev ranges, regardless of stroke length. If you use a two into one exhaust, the timings will need to be substantially different.
If the cam supplier has recommended timings, use those as a starting point then keep track of performance changes as you adjust the timing. - Difficult to do if you can only change it by one tooth on the sprocket at a time. Just remember one thing - YOU are in control.

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Did this when first setting up the cam. I used max lift calculation only to certify the cam timing was correct...it is.

RennieK said:

Have you tried larger main jets? Sluggish top end indicates main jets are too small.

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My thinking was the opposite. Had 260 mains and just dropped to 230 which improved it a bit. The worst performance was on Hwy 16 pass at near 10,000ft on the INOA Rally ride to Ten Sleep in Wyoming two weeks ago. That indicates it was running too rich and made me think to reduce the mains. Still no joy with this cam and will check to see if the reed valve on the engine breather is plugged. Last resort is pull the engine apart again this winter and insert a double S camshaft. I'd go back to the std camshaft I took out with a .080 Al plate in place of the head gasket except that camshaft has around 5 thousandths wear on the two of the lobes.

RennieK said:

Have you tried larger main jets? Sluggish top end indicates main jets are too small.

Click to expand...

My thinking was the opposite. Had 260 mains and just dropped to 230 which improved it a bit. The worst performance was on Hwy 16 pass at near 10,000ft on the INOA Rally ride to Ten Sleep in Wyoming two weeks ago. That indicates it was running too rich and made me think to reduce the mains. Still no joy with this cam and will check to see if the reed valve on the engine breather is plugged. Last resort is pull the engine apart again this winter and insert a double S camshaft. I'd go back to the std camshaft I took out with a .080 Al plate in place of the head gasket except that camshaft has around 5 thousandths wear on the two of the lobes.

Humm... the cam should increase the breathing capacity so it would want more fuel/air.

RennieK said:

Humm... the cam should increase the breathing capacity so it would want more fuel/air.

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If the engine is breathing more air the carburetor will automatically add more fuel without the need for bigger jets. Sometimes you will need smaller jets to make more power.
The needed jet size is determined by the shape and length of the pulse seen by the carb -not the engine size or horsepower. Of course the camshaft, compression ratio and pipe choice can certainly influence the shape of the pulse and the needed jet. Jim

The reed valve engine breather looks good, so I guess I've got a winter project. Seems easier to move on to a double S cam that I know will work than to play around with intake and exhaust tracts to get the Norris working. Please now suggestions to detune the combat

Got the engine apart and the Norrix RX camshaft out. Maybe this is why it didn't work well. It has around 500 miles service in my engine and didn't look like this when I put it in. I'm surprised an American made camshaft is soft. The lifters look as new, were reground at the time I installed the Norris.