High RPM RX cam for radiused lifters

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jseng1

jseng1

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The RX was my favorite flat lifter cam when I was racing my 850 Monoshock. Someone told me it was the best High HP, High RPM cam you could get for a Nort and I was convinced when I started using it. This cam has not yet been configured for BSA radiused lifters. I'm looking into that and I have contacted Megacycle to see what they can do.

I spent some time mapping out cam profiles and you can view the comparison between the RX and the PW3 below. Note the closing ramp difference below and how close everything else is except the ramp.

High RPM RX cam for radiused lifters


BTW - the Norris RX first came out as the HPI 7. George of HPI (horsepower international) told me it came from an Offenhouser grind. George is the guy who gave us the 920cc Norton.

Below is a comparison of the RX to the Axtell #3 (JS1)
High RPM RX cam for radiused lifters


You can see the general similarity in shape. Now the problem is getting the RX re-shaped to work with BSA lifters. I need some help getting the data I need to make or have someone make a cam master for the RX cam re-designed for BSA radiused lifters.
 
JS
you need to look deeper into the details behind the design of the PW3 and the RX than just the cam profiles.

On page 19 of 'About time for the spintron' I posted comparisons of the two cams, for the acelleration and jerk,and there you can clearly see a substantial difference exists between the two.

To create a version of the RX to be used with BSA type followers, first the radius of the follower has to be clearly understood. As manufactured by BSA, the radius was 1.25 inch, but you state on your web site 1.125 inch.

A small difference but important if the design is to be faithfully replicated.

On the Norris RX cam card, the LC was given as 108 degrees, and timing was shown as ex 82/54, in 54/82 at 0.020 inch.
 
Perhaps the shape of the follower on the cam grinding machine has to be the same shape as the follower you intend to use in the motor ? Or perhaps the inverse of the curve ? i.e. you might need a tube of the right ID (instead of a flat block) to get the grinder to follow the profile of the cam to make the copy more aggressive for the curved BSA type followers.
 
Snotzo said:
JS
you need to look deeper into the details behind the design of the PW3 and the RX than just the cam profiles.

On page 19 of 'About time for the spintron' I posted comparisons of the two cams, for the acelleration and jerk,and there you can clearly see a substantial difference exists between the two.

To create a version of the RX to be used with BSA type followers, first the radius of the follower has to be clearly understood. As manufactured by BSA, the radius was 1.25 inch, but you state on your web site 1.125 inch.

A small difference but important if the design is to be faithfully replicated.

On the Norris RX cam card, the LC was given as 108 degrees, and timing was shown as ex 82/54, in 54/82 at 0.020 inch.
Click to expand...

Yes there are plenty of details to consider. I use profile graphs because I can overlay them and compare them at a glance and search for the shape I want. The 1-1/8" radius applies to Triumph cams & followers which are more popular than BSA cams and the fact is that the cam suppliers use the same grind masters for different brands of bikes and run them on both 1-125" and 1.25" followers. The JS1/Axtell#3/megacycle NR/Webcam 312a is a good example and its available for both flat and radiused lifters and its sold for Norton, BSA and Triumph. The cam grinders are drowning in work and don't want to answer questions so I have to measure the lift/duration of all these cams, spec them out and test them. I can see profile graphs when I close my eyes now. Trying to get the grinders to deliver what you want is like pulling teeth without pain killer. Then they hit you with a $550 cam master charge. Then you have to beg them to deliver before you die of old age.

Megacycle won't even make the RX anymore so there is a real problem getting it reproduced - let alone having it custom made for BSA lifters. They still have the old RX master from Norris and it has been mothballed. Newman cams in the UK can take your data (lift and duration) and plug it into their CNC machine without having to make a "Berco" master. But with Newman cams there is a lack of customer feed back - who has used Newman cams and where are the quality/reliability responses?
 
Ugh what kind of Norton engine enticed the Norris D+ into existence and why so rarely used? I have only heard of its use by one VERY ADRENALIZED back to life half dead drag racer and Kelly George after spanking the shit out of two maxed out Maney 920 engines set up similar to Cummings & 1000cc National level XR Harley, giggling like a girl wanting to field the D+ this year. Something does not compute.
 
I think Phil Irving mentioned using a tool grinder that way. The mod you need for the RX cam probably only needs a different shaped follower on the tool grinder ? It might need to be a differential between flat and curved, have a look at the geometry and the maths.
 
Snotzo said:
JS
you need to look deeper into the details behind the design of the PW3 and the RX than just the cam profiles.

On page 19 of 'About time for the spintron' I posted comparisons of the two cams, for the acelleration and jerk,and there you can clearly see a substantial difference exists between the two.
Click to expand...

Snotzo
Yes I have studied your post and a 10,500 RPM cam without valve bounce is very attractive. One question I have is - at what point does the longer smoother ramp become too long? Will too much duration at low lift cut into too much time that the intake valve is closed during the compression stroke and reduce HP? You don't get something for nothing as they say and if the idea is to make HP then we have a conflict of interests - HP vs well behaved cams.

Hobot
The D+ flat lifter cam alive and well. Its the same as the Sifton 460 cam for radiused BSA lifters and the 460 cam was used in factory short strokes. Its also what I offer as the JS3 cam and the JS3 was in Dave Watson's 1000cc Nort that won all its races in UK classic open (2012) with Gary Thwaites riding (photo below). This is the most successful Norton roadracer in recent history and probably the only Norton that finished and won all its races all year long. The D+/Sifton 460/JS3 is a top end cam best suited for land speed racing, drag racing, short stroke screamers and large displacement motors on any kind track.

High RPM RX cam for radiused lifters
 
Hot diggity dog Jimmy top end big block power with some boost is music to my ears, hopefully w/o rpm straining the valve train just the exht valve melting. My teeth gritting pensiveness is everyone else in the world waits till apex to nail it while Peel allows nailing before pitching over by literally tripping down on lost rear traction with more power on tap to do it a few times in a row at increasing traction d/t more speed.
 
JS
you used the RX when racing so should well remember what the characteristics were.

Provided the redesign is a faithful replication of the original RX valve lift profile, nothing will change in that respect.

I ran a simulation with a titanium valve and the BSA follower, and your beehive spring. That the prediction indicated a valve train capable of operating without separation or bounce at 10500 was done to explore the limits of the setup.

The tool grinder adapted to grind cams is similar to the method used by Phil Irving when he ground up the original cams for the Vincent. Being a 1 to 1 copy grinder in effect, any error on the master is replicated on the cam being ground. Making a master x 5 the size of the finished cam effectively reduces any errors on the master by a factor of 5, giving a much more satisfactory end product.

Last year I saw Gary Thwaites race the Commando, and must say in Classic racing in the UK, a more impressive combination of man and machine would have been very hard to find. Unfortunately, I understand he is not racing the machine this year as it has been sold, but do not have any further details.
 
The two cam profiles overlaid, RX with flat follower, compared to the same RX valve lift profile, but generated from a valve train using the BSA radius lifter.


High RPM RX cam for radiused lifters
 
Yes Snotzo I studied your posts about the RX and also in the spintron thread.

The RX cam was all about mid range/top end and I loved it. Its the longest duration to lift Nort cam I know of and has the highest RPM capability before valve float and I needed it to keep my valves from rubbing each other. At the time my 850 monoshock was a top end motor. I basically used all the cam, port, intake, exhaust etc proportions I gleaned from the top running Axtell motors and scaled up everything in proportion to 850cc - with custom lightweight Wisco pistons to keep it from exploding. I was doing everything I could think of to keep up with the monoshock Ducatis. I could do OK with the 750s ducs but when the watercooled ducs came out I saw the light and gave it up.

The amazing thing about the Dave Watson/Gary Thwaites 1000cc Nort shown above is that he switched to Castor 40 bean oil and saw no wear anywhere at the end of the season - no bore wear and no cam wear. Bean oil is what the 500cc speedway racers and the Harley XR dirt track racers have to use in order to keep motors from destroying themselves. The problem is cleaning out hardened bean oil but someone recently posted that boiling the cases in antifreese is the way to do it. Sounds like a PIA but its worth it if you don't have to buy new parts.
 
Doesn't antifreeze contain glycol ? Boiling crankcases in it might be a bit of a headache for the unsuspecting. Graphiti remover might remove hardened bean oil, however it might also make you sterile - usually contains glycol ethers. (product name : 'Yuk off'.)


'I was doing everything I could think of to keep up with the monoshock Ducatis. I could do OK with the 750s ducs but when the watercooled ducs came out I saw the light and gave it up.'

I wouldn't hesitate to race an air-cooled commando against an air-cooled Ducati. The only air-cooled four-valve Ducati I've ever heard of was the one Bob Brown had Kevin Magee on in Victoria in the early 80s. I've often wondered why organisers never seem to recognise that technology differences are as important as differences in engine capacity. What sort of race class has both air-cooled and water-cooled four strokes in it ? I general terms a four-valve motor usually has 10% more go than the same capacity two-valve motor.
 
Snotzo said:
The two cam profiles overlaid, RX with flat follower, compared to the same RX valve lift profile, but generated from a valve train using the BSA radius lifter.


High RPM RX cam for radiused lifters
Click to expand...


What if a cam that was designed for BSA 1.25" radius lifters was run with 1.125" or smaller radius lifters - would it have a more gradual closing flank with a smoother closing ramp and less valve bounce?

Would there be some loss of HP because of reduced duration at mid lift?
 
With a smaller radius lifter - The lift rate would be less aggressive at low lifts and more aggressive at high lifts, so more likely to cause float. And the duration would be shorter due to the effect of the smaller radius on the tappet clearance. You would turn the cam slightly further before it started to lift and the closing point would also be earlier. It might affect where in the rev range the power band started. I doubt that you would feel the difference, however it might take the edge off the performance - particularly the way the cam spot happens. I think flat followers are less likely to cause valve float.
 
Snotzo said:
Last year I saw Gary Thwaites race the Commando, and must say in Classic racing in the UK, a more impressive combination of man and machine would have been very hard to find. Unfortunately, I understand he is not racing the machine this year as it has been sold, but do not have any further details.
Click to expand...

Gary is currently racing a 750 triple, and who knows where the Watson Nortons went? But this year in UK classic racing we have seen 4 more Norton 750s, 3 from France racing in F750, two are father and son, the young Frenchman in particular is very fast and beat Gary at least once over the weekend, which was pleasing. Could be pleasing for Jim since all 4 sport JSM parts.

Oh! and the 4th bike?, well I got a full weekend of 8 races on mine, trying my best to get past the 3rd of the Frenchmen :D.
 
Brooking 850 said:
SteveA, any pics to share?
Regards Mke
Click to expand...

First photograher has posted Saturday only so far.....typically 3 guys will post, should be some more around by Wednesday...
 
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