Combat with Norris RX camshaft

The Norris R was their streetable grind that would work with mufflers. The RX did not work really well with mufflers, it was a good roadracing cam to use with open meggas. The D was a big drag cam.

I got this information from T.C. Christensen about 20 years ago when I bought a few NOS Norris cams from him.

Here is a Norris Rx on a Dominator core with it's original springs, sheets etc. :

http://www.facebook.com/photo.php?fbid= ... =3&theater

Been playing with tuning the combat engine with Norris RX cam over the weekend. It wasn't getting much power beyond 5000rpms. Plugs were very light colored. Went from 240 to 260 main jets on combat 932/19 932/20 carbs and it improved. Jury is still out if I like this cam. Good news is it revs better than with the std cam. I going to stay with it for this season and see. Fun public road riding only. Should be interesting in August when the club goes for the Dardanelle weekend camp out. Sonora Pass road is nearly 10,000 ft elevation. Kinda takes the poop out of the power.

I had a Norris "R" cam in my 1969 Commando. Spec timing. It ran like a thief in the night. Top end galore.

Hi Steve, what were your cam timing , with that Norris RX ? I had understood you have the Comabat head , so 10/1 (ish..) and 32 mm amal .........may be you can advanced it slightly.........hope to hear more info from you, about that cam , always interesting , those tec tales.

Just checked the right intake cam timing for reference over the weekend. Norris RX spec is 54 degrees BTDC at 0.020" lift at the rocker. Mine was at 56 degrees BTDC....close enough. That's when I went after the main jet change and got improvment increasing from 240 to 260 (932 Amals).
JimC... I'm still not completely impressed with the power above 5,000rpms and will continue to play with jetting and maybe timing.

I had a "R", you have a "RX". Someone posted the "RX" needs open megaphones to come alive. It's a Roadrace cam.

JimC said:

I had a "R", you have a "RX". Someone posted the "RX" needs open megaphones to come alive. It's a Roadrace cam.

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Saw that post also. Last year another post mentioned he had used and liked the RX grind for street. "opinions vary" I'm going to continue working with this cam for this riding season. Not really a big issue to change next winter. Opportunity and the fact that a local expert told me to stick to US made cams were the reasons I went with this one. My goals are eliminating the pinging I was getting with the previous cam and restore "combat" performance while keeping the machine roadable. Not there yet on the performance part.

The Norris RX cam was originally developed for Nortons by HPI (was his name George?) He also developed the first 920s

HPI told me they got the cam profile from an old Miller-offenhauser grind.

It happens to be nearly exact in proportion to the Axtell #3 - just blown up.

I used one in my 850 monoshock (see at the JSmotorsport website).

Its definitely for rock & roll.

LOTS of duration but not too much extreme lift so you can rev the bejesus out of it before valve float.

Help me get some concepts and working geometry straighter on cam valve train.
If a flat lifter cam say a Norris D+ had a a bit too much lift or duration is is possible to alter the factory lifters to reduce duration and/or lift? If so how so?

Hi Steve, I am asking myself the same question, but with the RX , as I have one under hand and after seeing the long duration, why not fit the JS caml followers, to reduce a bit it, what could be the result, once I had asked to JS but he was not so keen on that way, after asking to J Comstock the radius of the BSA lifters (1" 1/8, his answer) , we must do some maths to calculate the results !!! but AFAIK no change in lift , just duration.

Yes radiused lifters will reduce duration on flat tappet cams but you have to do you own calculations. Going to 1-1/8 radiused lifters is going a bit far. I used to cut a 6" radius on flat tappet lifters when I didn't have enough valve clash clearance - exhaust side only.

Just for reference I went with flat tappets - resurfaced. Increased duration was my goal. Correct me if wrong, I believe the lumpy idle is from the 108 degrees overlap on this cam. Some of you with experience could help me if you have suggestions for jetting Amals and best ignition timing.
Current - 932 with 260 mains. Lucas RITA set to 28 degrees BTDC at 5000rpms.
Amals were sleeved by Mike Gaylord in 1998.

illf8ed said:

Just for reference I went with flat tappets - resurfaced. Increased duration was my goal. Correct me if wrong, I believe the lumpy idle is from the 108 degrees overlap on this cam. ................................

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and

illf8ed said:

Just checked the right intake cam timing for reference over the weekend. Norris RX spec is 54 degrees BTDC at 0.020" lift at the rocker. Mine was at 56 degrees BTDC....close enough. ................................

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At face value, the intake opening and closing two degrees earlier would provide a slight broader mid range at the slight expense of top end performance BUT you are a "flatter" lifter for increased duration so the original timing specs you cite will no longer be valid.

You may want to consider looking at lobe centers for setting/checking cam or go back and see where the intake valve closes and compare to the original cam spec sheet. This may be why the lumpy idle ................or it could be a bunch of other things.

Forever and a day the main thing used to tame cams to idle lower and more steady is by upping the CR. Next thing is increase the displacement over what the cam was originally designed for. Third thing is smaller ports to up velocity some to pack in mixture at low rpms. Fourth thing is bigger valves. Fifth way is retard ignition. Sixth way is advance the cam degrees so intake valve closes a bit sooner before mixture flushed out-diluted by exhaust back pressure or sound wave. Seventh way is getting header length and size the muffler baffle 'righter' plus effective 2 into one extractor dialed in. Eight thing is longer stroke crank that jerks piston down faster off TDC than shorter stroke. Ninth way is heavier fly wheel. Last way is add some pressure boost into the intake.

jseng1 said:

The Norris RX cam was originally developed for Nortons by HPI (was his name George?) He also developed the first 920s

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That would be George Gjonovich, owner of Horsepower International (HPI) in Garden Grove, California. George was quite a charcter, well known for his 920 kits and nitrous setups. I'm still running one of his iron 850 cylinders that he sleeved out to 920 size. And somewhere in a box I've got one of his first nitrous kits. The jets for nitrous and fuel were just brass tubes soldered shut, with small holes drilled in them. I think he was the first to put nitrous on a Commando. George died in 1999.

Ken

hobot said:

Forever and a day the main thing used to tame cams to idle lower and more steady is by upping the CR. Next thing is increase the displacement over what the cam was originally designed for. Third thing is smaller ports to up velocity some to pack in mixture at low rpms. Fourth thing is bigger valves. Fifth way is retard ignition. Sixth way is advance the cam degrees so intake valve closes a bit sooner before mixture flushed out-diluted by exhaust back pressure or sound wave. Seventh way is getting header length and size the muffler baffle 'righter' plus effective 2 into one extractor dialed in. Eight thing is longer stroke crank that jerks piston down faster off TDC than shorter stroke. Ninth way is heavier fly wheel. Last way is add some pressure boost into the intake.

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Hi Steve,

Wasn't trying for science fair project with this cam...only changed from the standard cam to improve pinging and provide combat performance in a combat engine. My plan is to see if the RX can be made to work through adjustments without any more modifications. Failing that I'll pull it out next winter and find a cam that will work within my criteria.

Thanks,

David

For what it is worth, the first order of business would be knowing where you are starting from. I would plot the cam profile with your flatter lifters and find out where lobe centers are.

As for tuning, tuning of the intake and exhaust lengths and configurations is the stuff you don't have to pull the head or motor down for. After initial jetting I would have a go at intake and exhaust tuning if you are inclined to do so.

Lots of imperical formulas out there to get you in the ball park. Maybe someone on the list can get you to a good starting point.

Dances with Shrapnel said:

For what it is worth, the first order of business would be knowing where you are starting from. I would plot the cam profile with your flatter lifters and find out where lobe centers are.

As for tuning, tuning of the intake and exhaust lengths and configurations is the stuff you don't have to pull the head or motor down for. After initial jetting I would have a go at intake and exhaust tuning if you are inclined to do so.

Lots of imperical formulas out there to get you in the ball park. Maybe someone on the list can get you to a good starting point.

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Hi Dances,

Norris specifies flat cam followers for RX grind. Cam centers aren't going to move with either flat or radius'd followers, however I believe what you mean is you can't rely on initial valve openning to be certain cam center is where it's supposed to be. I'm taking that on faith and American cam maker's reputation.

Explain more on tuning intake and exhaust "lengths". The only variable I can imagine is tappet clearance unless you're referring to duration - time the valve is open. Then we're back to cam follower radius.

Thanks,

David

Wasn't trying for science fair project with this cam...only changed from the standard cam to improve pinging and provide combat performance in a combat engine. My plan is to see if the RX can be made to work through adjustments without any more modifications. Failing that I'll pull it out next winter and find a cam that will work within my criteria. Thanks, David

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Hehe oh yes you are David, even if only high school level you are helping my science fair project to thrive and survive too. We've example of RX working a treat on Combat so yours should too. I've been sorely depressed on dull performance down low through top end on Peel's 2S cam to point I sought some comic relief nothing more to lose by 12 ga slug blast though stupid Surpertrap end cap - so next ride out my driveway in depressed low energy mood of slack grip and seating ho hummed a throttle snap expecting worse bog cough slowish chugging pick up > to almost get left on the ground w/o a bike under me!!! WHAT!!??? So gripped tight and hunkered down on next snap > WOWEEE. I had to develop new reflex pattern before end of my 1/2 mile drive to 1st death grip bars and plant butt before 1st extra twist on throttle in 1st and 2nd.





There is an Eleventh way to help tame big cam idle that involves opening up the pilot jet so takes less air speed flow past venturi to get fuel enough to burn predicable. I don't know how to do this on Amal or Miki or flat slide carbs, just how its done on butter fly automotive carbs, which also involves cutting notch over the idle fuel port or other hole placed away from port to allow extra easy air entry w/o moving the butterfly off the idle port notch/groove suction draw area.

Hello illf8ed,

I took it that you went flat for increased duration but if flat is what the cam was specified on then your measurements are close enough. The cam may be set to slightly favor top end performance with a later intake valve opening (thus closing).

What I was trying to say was, if you were using flat lifters and the specs were for radius lifters, then you would have to use lobe centers to set timing or split the difference between opening and closing event and adjsut accordingly. A single point degree measurement would not suffice (ex IN open of IN close at a specified lift) as you would be comparing apples to oranges.

I do see earlier in this thread where the pictures of the spec sheet show two sets of cold lash settings, 0.006/0.008 and 0..13/0.013. The questions is which ones are correct. I am assuming you are using a cast iron barrel with alloy push rods. If you are using alloy barrels and/or steel pushrods you need to make adjustments to the valve lash specifcations to accomodate the different thermal rates of expansion.

Assuming your intake tract and exhaust primary pipes are stock, for tuning intake and exhaust lengths, to take full advantage of the new valve timing you may want to consider lengthening the intake tract for starters and see how the motor responds. This takes dyno time and/or lots of seat time. Same with the exhaust pipe length although I don't know where you would start (lengthen or shorten). There are imperical formulas out there to calculate primary pipe length and then see if the motor is happier with the change. Lots of texts books and on line references for this subject matter.

I would start with jetting and if you can get it on a dyno with an exhaust gas analyzer to see where you are at.