FEATHERBED RAKE ANGLE

I am building a special using a slimline featherbed which I think has a bent headstock.. Does anyone know what the correct angle is of the headstock with respect to the bottom frame tubes?
Matt

Don't you like the answer you already have been given ??

Cheers !

Unfortunately, I been given 5 different answers stretching from 22.5 degrees up to 27.5 degrees. Which do you think I should 'like'?

Take the frame to someone with a proper alignment jig, and get them to check whether the headstock lines up with the swinging arm pivot, and if not get them to straighten it out. If the frame itself is obviously damaged, or if the engine no longer fits, someone with a proper jig who knows what they are doing should be able to get it sorted out.

You misunderstand the problem. There is no such concept as a headstock lining up with a swingarm pivot. On any motorcycle, the headstock should be at 90 degrees to the swingarm pivot and hence the rear axle ( normal to the front or rear planes). My frame is correct in this respect. Another headstock deformation could be left or right planar - again my frame is correct in this respect.
My problem is with the angle of the headstock in the side-on plane (this will dictate the rake and thus steering and handling characteristics as well as affecting mudguard clearance). The first question a professional with a motoliner jig will ask is ' what should the angle of the headstock be at?' For a modern bike these figures are available in the manufacturer's specs and every motoliner owner possesses a comprehensive list of same. However, I have found the figure for a featherbed to be difficult to find - everyone seems to have a different answer with up to 5 degrees of difference - I might as well stick a pin in the list and use whichever the pin lands on. I find it perplexing that for the most famous motorcycle frame ever, with thousands of specials built using it, and every single edition of every 'classic' motorcycle publication in these last 30 years referring to it at least once (with plaudits ad nauseum regarding the steering and handling), - that nobody seems to know the angle of the headstock as supplied from the factory. Has nobody ever crashed one, has nobody ever had to straighten one, does it not matter 2 damns what rake you put on a motorcycle - I think that chassis designers and works team frame tuners would think otherwise!
If anyone knows the 'correct' headstock angle, please respond.
Matt

hi matt,i think i answered this same question a while ago,with info gleaned from roy bacons norton twin restoration book,however my brother in law has borrowed the book so i cant look it up till i can get intouch with him,will also recheck my posts again to see if i can find it

hi matt,i checked my old posts{brother in laws in the pub lol}the numbers i have are from roy bacons book,manx and wideline=26 deg,slimline =24 deg 750 commando=27 deg 850 commando =28 deg hope this helps

And, not surprisingly, this agrees with the measured diagram posted on the NOC website.
These details are everywhere, for those that look....

http://www.nortonownersclub.org/noc-cha ... IMLINE.jpg

Thank you all sincerely for your replies - they are much appreciated and I am sure given in the true spirit of biker to biker assistance.
Unfortunately, none of the figures agree with those given by Ken Sprayson (the well known and highly respected frame guru who oversaw all the featherbed production at Reynold's Tube), as interviewed in Classic Bike October 1981. Ken is reported in the article (a review of the 650ss) as saying that the frames as manufactured did not match the Norton Featherbed blueprint angle of 64 degrees (ie 26 degree rake), but that they were actually 62.5 degrees (ie 27.5 degree rake). In other reported conversations with Ken on the same topic he has been reported as saying that all the frames (wide or slim) have the same headstock angle.
I have been unable to find a method of contacting Ken to enquire into the veracity of these reports, but I AM STILL TRYING.
With regard to Mr Bacon's figures, I have in the recent past read criticisms of his publications as being over reliant on manufacturer's officially produced data.
Again thank you all, I am not trying to be awkward. I just wish to ensure that when I entrust my frame to a Motoliner professional that I am able to supply him with the correct headstock angle which I wish thim to achieve through the bending process. When you pay to get a frame straightened you would like to think that at least the headstock is correct - various other tubes/dimensions may be unimportant (indeed, crosstubes on featherbeds seem to have been positioned by eye rather than to a particular measurement or squareness).
If I can contact Ken, I will let you all know 'the last word' on this topic.
Matt

Ken Sprayson as far as I know worked for Reynolds not Norton, and while some Featherbed frames were made from Reynolds tube, most of them were just cheap gas pipe. If you are in the UK then contact Maidstone Motoliner, who will almost certainly be able to help, as they have been involved with classic racing for decades, and will almost certainly have the information to hand. Bearing in mind though the fact that new Featherbed frames are easily available, and they are not that strong a design in any case, so if its anything other than minor damage it might be worth looking at a new replacement?

1/2 a degree is probably less than the +/- manufacturing tolerance for frames back than !?

Just welding everything up could move it that much ? Even in a jig. Booiinng ! when it comes out of the jig. Then, put it in the enamelling oven for several coats - and then measure what angles come out ?? ....

If 1/2 degree is such a big problem with this build, then surely its going to be much easier to simply buy a new frame?

My guess is that if the frame tubes appear undamaged, they ARE undamaged.

The criticality of the (one of the?) original rake angle(s) is only pertinent if you are intending to restore the bike to concours condition that could be verified only with a frame jig, and then the differences in the several possible rake angles would only be percieved by a VERY highly experienced rider. Whether the resultant rake angle (if indeed, "correct" one) would be desireable to YOU (if you intend to ride it) would remain to be seen, and may depend on having the correct yokes and forks.

The few degrees between the figures mantioned (for featherbed framed bikes, NOT Commandos), is fairly narrow. Certainly you can measure the frame and decide if you think you'll like the measured result; "tight" / "quick" steering, or "slow" steering response, for your intended riding style?

The rake angle on my 59 Wideline measured up at being 24°, this seems correct and is the same as the NOC details. I believe that both the wideline and slimline have the same angle of rake.

Webby

What datum is the 24 degrees being measured from I wonder?

Again, thanks for all contributions - although I fail to see where some are coming from.
From what cloud has this figure of 1/2 degree come from.
My quandry is very simple and I think very valid: to date I have received headstock angles varying from a tight of 22.5 degrees to a wide of 28 degrees - a difference of 5.5 degrees not 1/2 of a degree - a major difference which has nothing to do with concours judging but everything to do with safety.
To further muddy the waters, check out this contribution to the NOC forum in January 2011 from former Norton employee Bill Cakebread: ".............................. front mudguard from fouling the frame on the Featherbeds. This was one of the warranty problems that we found when production was moved to Plumstead. I was the draughtsman assigned to investigating why it was happening and I found that the frames were being made with a head angle that was 2 degrees closer to the vertical than was shown on the drawing" - this info seems to be in direct conflict with that attributed to Ken Sprayson in '81, although of course we are talking about frames manufactured in different decades (but, we are told, made on the same basic jigs).
Rohan, I am fully aware that Ken Sprayson was an employee of Reynolds; they were contracted to make production featherbeds in quantity. The production details were hammered out in the spring of 1950 in meetings between Norton's Gilbert Smith, Reynold's Ken Sprayson and my former neighbour Rex Mc Candless.
Enough is enough. Unless I am able to contact Ken and he informs me to the contrary, I have decided to go with 27.5 degrees - just today I have received info from Maidstone Motoliner which reinforces this figure; it is a long way off the 24 degrees which some contributers have insisted upon.
Thanks for the craic.
Matt

Whats the angle at the moment, and how far will it need to be moved to be at the figure you have decided upon? Interesting that Reynolds were responsible for building the Featherbed frames, as I understood that most were made out of cheap gas pipe, and only the competition types used Reynolds tube.

Matt,

I don't think either of the extremes (in the several rake angles mentioned) would result in a DANGEROUS bike. Perhaps some minor front fender damage at worst.

Press on...

At the moment my headstock is at an angle of 67.5 degrees with respect to the frame bottom rails ie 22.5 to the vertical, so I will be pulling it by 5 degrees - I first twigged that something was wrong when I realised that even with a thin fibreglass front guard fitted to be absolutely 'kissing' the tyre, there would still be a clash if full fork dive resulted from emergency braking - the possibility of having a front wheel lock-up due to a clash with the front downtubes is not a reassuring thought as you are heading 3 abreast into an Irish hairpin with each rider looking to get onto the same piece of tar.
On discussing the front wheel clearance problem with other NOC members I soon discovered that many had experienced 'clashes' when riding 2 up and carrying luggage - they were aware of the inherent danger but were willing to take the chance and when fully loaded rode with extra care to brake well in advance of obstacles. All very well, but not very practical when you are racing or even 'playing' at racing.
With regard to tubing, I have never heard of 'cheap' gas pipe being used by Reynolds for frames although I'm sure they manufactured (and still do) numerous grades of tubing for numerous applications. I am open to correction but to the best of my knowledge the Manx frames (and possibly some Inters) were made from grade 531, a manganese alloy tube first introduced in 1935 (50 ton tensile strength before bronze welding), with the joints bronze welded (this is not brass brazing, nor indeed is it any form of welding). The production frames were made from cold drawn seamless mild steel tube which was apparently available in different grades ('A' for the Inters, 'B' for the roadsters) with the joints welded (welding created problems with 531). The modern successor to 531 is 631 along with its heat treated cousin 831, both of which can be TIG welded without problem and indeed is the favoured method of jointing as joint durability is improved over the bronze welding method. Some modern frame makers favour T45 or its American equivalent SAE 4130.
Keep her lit
Matt

The angle in respect to the bottom frame rails is immaterial.............the angle of a head stock is generally related to its relationship to the ground on which a bike is standing when fully assembled.

However if your front wheel is contacting the down tubes though, your frame is almost certainly bent as long as the fork tubes and wheel are correct and have not been "modified" for some reason or another. I would suggest caution in attempting to straighten a relatively weak frame such as the Featherbed by as much as 5 degrees though, as cheap MS tube will be made even weaker, after being bent through 10 degrees adjacent to HAZ, and the result of outright failure on a race bike may have very serious consequences!

531 tube is still being made, but is now manufactured in the far east. German manufactured 631 is a tube originally developed for cycle use, and is air hardening which allows tubes to be joined using the TIG and Mig processes, both of which are superior to bronze "welding", which was linked directly to the failures of 531 type tube sets, that led to the introduction of 631. At the moment very few motorcycle frame builders are using this tube, as it is relatively expensive and untried in comparison to other alternatives, but on paper motorcycle frames made using a combination of 631 and 831 tubes seem very interesting, although impact damage may be a problem in some competition applications.