Article on featherbed frAme

Peter Williams, on one of the early JPNs.
Was little more than a hotrod Commando at that stage.
Did a 107 mph lap, which was more than a manx...
(And 750cc against 500cc of course).

Details from memory, without checking exact mph numbers.
Oh cynical factless doubting thomas...
Surely you knew that ?

No I don't know much about the JPN effort before the 1973 win.

IMHO the difference in the actual pipework between featherbed and Commando amounts to naught.

The better handling bike will be the one with the best tyres, suspension, forks, and attention to detail with regards to set up and fine tuning.

Whilst my Commando has a high speed weave ONLY when in high bar Roadster spec, in 'track trim' it handles at least as well as any old Brit I've ridden (seat of the pants judgement only). It is far from stock of course, but the basic frame is untouched.

But this does not prevent me from planning / dreaming of building a hot rod Commando engined Manx framed track toy !!

Nearly everyone likes the look of those curved rear frame tubes on the Featherbed. One question might be- Is the look of a frame tube worth introducing some additional vibration to your ride?
Various balance factors might help, but a solidly mounted 650ss, Atlas, Commando 750 or 850 is never going to be as smooth as the isolastic Commando. Some bias here, but my trials of various Commandos indicates the MK3 is the smoothest of the smooth.
The amount of vibration one finds tolerable seems to be highly variable, probably dependant on the age of the rider and the miles ridden per day. On long hauls, vibration wears out everything, including the rider.

Glen

The later John Tickle Manx's - the T5 etc - had frames made from largely straight tubes.
Not sure that they were any slower or faster in the slightest.
No idea about vibration levels...

worntorn said:

Nearly everyone likes the look of those curved rear frame tubes on the Featherbed. One question might be- Is the look of a frame tube worth introducing some additional vibration to your ride?
Various balance factors might help, but a solidly mounted 650ss, Atlas, Commando 750 or 850 is never going to be as smooth as the isolastic Commando. Some bias here, but my trials of various Commandos indicates the MK3 is the smoothest of the smooth.
The amount of vibration one finds tolerable seems to be highly variable, probably dependant on the age of the rider and the miles ridden per day. On long hauls, vibration wears out everything, including the rider.

Glen

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When I built my Commando Featherbed I got a lot of work done while the motor was apart, Ivan Thigt in Brisbane was well known cam builder, so I took my cam to him to get built up to a SS grinde (2S grinde to some) while there I told him what I was doing and needed to get my crank balanced, he put me onto a old English gentleman who done balancing work, he was just down the road so I went and had a chat with him, I told him what I was building and then he started to throw numbers to me about the right balance factoer for the Featherbed to Commando combination, he told me what to bring over and a week later my crank was balanced ($42 for the balancing) what ever he done he got it spot on as my Featherbed is so smooth to ride, yes it does get a little vibration at serten revs in the foot pegs but its not to bad, this was my everday ride for over 30 years, I have done so many long rides on this bike the innerstates seat helps with that I can ride all day without any problems at all and when out on the byways I normaly cruise between 65 to 90 mph, my point here is I reacond its as smooth as when the motor was in the Commando frame, but I will get others who will say BS but hey I know my Norton, I ride a few Commandos as I am aways working on my mates Nortons and the ones that I have let ride my Featherbed are very impress with it how smooth it is for a hard mount motor and they can't believe how light it is and how well it handles, but when my mates ask about their isolastics I just shy off, I leave that to them to sort out.

Ashley

ashman said:

so I took my cam to him to get built up to a SS grinde (2S grinde to some)

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We've had this discussion before !

The std Commando grind IS the SS grind, same as the 650SS and Atlas had.
A 2S grind is the Combat cam.

So, strictly speaking, an SS grind - written like that - in a Commando is a stock cam.

In my workshop manual that I have since 1976 it has the high performance section in the back and I built my motor to the stage 1 speces for road and the stage 2 speces is for racing, in the stage 1 build they say to put a SS cam in for better performance on the road and the stage 2 to put a SSS cam for racing, if as you say a SS cam is a stock cam then why would you build a high performance motor with a stock cam, well I know my SS cam has more lift than a stock cam and yes I did measure it to a stock cam, I am building my Domie up and I am putting a Combat cam in it which in the early days was classed as a SS cam.

So really Rohan I couldn't give a s..t what you say, the way I see it SS and 2S are the same, just the way its written, you know what part of Australia I live but why don't you put where your from, anyway you are welcome to come around and look at my workshop manual to prove me wrong but I am not going to agrue with you over 2 letters to 1 number and 1 letter, who friggen cares.

Ashley

ashman said:

In my workshop manual that I have since 1976 it has the high performance section in the back

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Obviously not a factory manual if they are not using the names the factory used.
As we have pointed out before - other folks may need to be aware of these things...

http://atlanticgreen.com/camsurvey.htm

22729, 650SS and later 750 Atlas grind with common X2 marking on the twin chain core, know as SS

061084 This cam grind started as the 650ss cam shown above, by now it's called the 1S for the commando, it is the standard cam grind for all non combat 750 and 850 comandos. Lobe centers are 100º

063536 The famous or "infamous" 2S combat cam. Note*** this is MARKED "SS" on the camshaft, but it is not the 650SS (1S) grind

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Yes, that SS and SS/2S cam is (still !) the source of much confusion.
Factory based names too.

Basically what I said. Allowing for Dave's writing style - could be clearer. (?).
But, where does the factory ever call a Commando cam a 1S ??

BTW, I've got an Atlas cam with X1 on it, so not all is explained there...
The X1 & X2 were reportedly the hardening process (??).

BTW2, speaking of being clearer, what does "Lobe centers are 100º " actually mean here ???

We diverge muchly from featherbed frames here, methinks ?