FEATHERBED RAKE ANGLE

Matt,
I think you are getting your stories mixed up here.

YOU mentioned 24, and the 24 1/2 degrees. That is a 1/2 degree difference, is it not. ?

The diagrams I have seen for the slimline are 24 degrees.
Other featherbeds are different angles.
There are near 20 different versions of featherbed, all up.

I didn't say anything about Reynolds and Ken Sprayson. Someone else did.
But since we are here, Nortons in the early 1950s and in the slimline era are 2 different companies. In 1950, Nortons knew nothing about welding frames - all their expertise was in hearth brazing of lugged frames.

Are your fork yokes and tube lengths and ride height correct ?
In 50 years, lots can get changed to make things wrong...

Folks here are nuts for suggesting a new frame will correct a minor problem for a frame repairer.. AND, there is no-one currently doing a repro slimline anyway ?

Cheers.

A cheaply made relatively weak MS frame thats been bent through 10 degrees adjacent to a HAZ is not suffering from a "minor" problem. New Featherbed frames made from far higher spec T45 tube are easily available from several builders here in the UK, but one of the better known ones is http://www.unityequipe.com/html/products.html

Unity make Wideline frames.
I've seen them say publically they would not touch slimlines....
At that price, that would pay for a lot of frame repairs.

And who know what angle(s) they build them to.

Its that curved tube design that is weak if stressed too hard...
Manxes (which all used widelines) didn't even have the massive bracing under the headstock...

Its simply not possible to safely "repair" cheaply made MS frames bent as much as the OP suggests, as fatigue failure is a very real possibility after MS pipes have been badly bent very close to the HAZ resulting from crude MIG or MMA welding processes.

New frames are easily available from Unity in wide or slim versions, and being made out of T45 rather than gas pipe, handling is likely to be quite a bit better, and would be the correct option for anyone who intends to use a bike seriously, and doesnt want to worry about problems with cracking (or worse!). http://www.unityequipe.com/html/products.html

Its extraordinary that people seem willing to badly compromise safety to save money, and are seemingly quite prepared to risk the safety of others at the same time! I would suggest contacting a pro frame builder about this "repair", but would be very surprised if anyone would advise that a rather weak MS frame bent through 10 degrees in a highly stressed area, would be safe for further use.

Repeat, Unity don't do slimline frames ?

Where did this business of being bent by 10 degrees come from ?

Perhaps you've not heard the story of the original wideline featherbed roadbikes ?
The earliest ones didn't have the gusset bracing under the steering head - as neither did the manx. Didn't take long before folks noticed the roadbikes handling changed, and the steering characteristics were different - yep, the steering head angle had altered. Investigation put this down to running over gutters and the like - and large gusset bracing was fitted around the steering head of all further road bikes. Don't know what happened to the actual bikes with this problem - were the frames discarded, or repaired ?? Manxes never got the bracing, leading a pampered life they didn't get to hit gutters etc (ha ha ?).

Shades of the early Commando frame problems - history repeating ?

I've got some retweaked frames - as long as they have not been bent beyond their elastic range, they are no more likely to break than a new one ? In fact, hi-tensile tubing is supposed to have a shorter working life. It was originally envisaged that Manx frames would only have a working life of several years (unspecified) as they lost their 'spring' after hard use - as every cycle racer knows...

P.S. Manx racing frames are actually in thinner lighter (and hi-tensile) tubing than the road frames.

Anyone sighted any studies of the relative strengths of the various frames, this should make the thicker walled road bikes stronger. ? In theory...

Sorry if this is all a bit complicated............If head angle differs 5 degrees from the factory figure, then it will need to be moved back 5 degrees to meet the factory spec, which taking into account original deflection (5 degrees) means it has been moved 10 degrees in total.

If we are talking about an old original race frame here rather than one made of cheap ms pipe, then bending old rather brittle 531 tube 10 degrees is even more likely to cause problems, and this is the primary reason vintage aircraft made out of high tensile lightweight tubes have any damaged tubes replaced, rather than run the very real risk of fatigue failure due to having being straightened.

The Unity reference to provision of new slimline frames on their home page http://www.unityequipe.com/html/products.html must be wrong, but if so there are several sources of these frames here in the UK, which would seem to be worth investigating before bodging a damaged original which might turn out to be lethal.

I suspect that frame damage over time would result in the clearance beween front wheel/fender and anything in the chassis would INCREASE, not decrease...

Interesting point of view, and quite possible if the headstock area is cracked, or is badly fatigued wheelbase becoming longer is quite possible. The most common damage on motorcycle frames though occurs after bikes have been crashed into something solid, or been hit front on by a car for instance.

This often results in the top tubes of the frame bending, and not as is often thought the head stock being bent backwards.........reason for this is the front of the bike coming to a dead stop, which will most often cause the top tubes to bend, as the back end of the bike continues to move forward, which obviously alters the head angle.

Featherbed Norton frames seem to be relatively weak, with the not much support in the area of the swinging arm pivot, and the design meaning its very difficult to put much strength into bracing the steering head area.

Personally I would say that most of these frames if they are original will most certainly be out of true to some extent, and checking the wheelbase against factory figures is likely to be a much better and easier way of assessing this, rather than attempting to measure the steering angle.

To check the wheelbase simply get a long straight plank of wood, and accurately mark on it the factory spec wheelbase (with chain adjusters in middle of movement), then lay this alongside your wheels and see if the tyre contact patches are anywhere near the factory spec. Its not likely to be a small difference, so if the frames distorted it will be quite easy to see this, indicationg an overly long or too short wheelbase.

Carbonfibre said:

not much support in the area of the swinging arm pivot,.

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Are you mad?

The significant difference between the Norton frame and almost all it's rival frames is that it has "support in the area of the swing arm." If you mean to say that something like a Suzuki GSXR has more support there, what can I say except "So what?"

Carbonfibre said:

The Unity reference to provision of new slimline frames on their home page http://www.unityequipe.com/html/products.html must be wrong, but if so there are several sources of these frames here in the UK, which would seem to be worth investigating before bodging a damaged original which might turn out to be lethal.

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Unity do mention Slimline frames on that page, but it also seems to say there's only one type available. I've never heard of anyone making replica Slimlines. Why would they? There can't be much of a market.


Straightening bike frames isn't a bodge. You could be taking a bigger chance buying something claimed to be a replica. Unity's frames had better be more accurate than their exhausts!

Triton Thrasher said:

Carbonfibre said:

I've never heard of anyone making replica Slimlines. Why would they? There can't be much of a market.

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Someone here in Oz was making replica Atlas frames (i.e. slimlines, one version of).
This after the supply of frames/parts from the US dried up, after ebays QueenG (?) shut up shop. He did a slimline modern Hinckley Thruxton, very neat cafe racer. Frame was tigged up, lovely work. Head could come off in the frame. Pic was shown to Unity - have to take the motor out to take the head off in their version, tricky even to do the tappets.

Problem with replica frames is the numbers and vin plates.
If its modern, it needs approval and compliance etc etc blah blah blah?
Jig and stuff was sold, new mob have gone quiet.

Cheers.

Carbonfibre said:

Its simply not possible to safely "repair" cheaply made MS frames bent as much as the OP suggests, as fatigue failure is a very real possibility after MS pipes have been badly bent very close to the HAZ resulting from crude MIG or MMA welding processes.
.

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Are you mad ?
Have you seen a frame repairer at work ?

Anything that is more than slightly bent is reworked HOT, to pull it back into line.

If you count up the number of times steel gets hot in its manufacture, one more time is neither here nor there. Care has to be taken with hi-tensile tubing, but we are not discussing hi-tensile here.

Carbonfibre said:

Featherbed Norton frames seem to be relatively weak, with the not much support in the area of the swinging arm pivot, and the design meaning its very difficult to put much strength into bracing the steering head area.

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Have you looked at a roadgoing featherbed frame ? !

The bracing and gussets around the steering head mean it can't go anywhere - unless its hit something serious.

P.S. If it is really bent, creases in the tubes usually show where this has happened.
Talk here of bending something back to 27 degrees (when it never was 27 degrees !), with no sign of bending, is going to make this featherbed into a camel..... ?

The Featherbed frame is inherently weak, as there are long runs of tube which are not supported and have no cross bracing of any kind. However they were a step forward from the hearth brazed and lugged frames commonly used in the British motorcycle industry, as they could be produced faster and more cheaply.

Annealing ms tube will weaken it significantly , and greatly increase the chances of bending in future...............but if anyone wants to take a chance on trying to repair a scrap frame rather than buying a new one, its really up to them, but personally I would rather opt for a new frame if major damage involving bending far over the elongation limits of tube was involved.

What is this 'scrap frame' business ??

The initial post here was for a frame with no obvious or visible damage, where Matt was enquiring the angle of the steering head. His measurements sound to be maybe a degree or a degree and a half off the quoted specs for this - with the proviso that this is relative to the lower frame rails. Which may or may not be a valid measurement anyway - no one conversant with Atlas frame measurements has chimed in yet, and the bike is unassembled so can't be measured as a rolling chassis.

Geez, he hasn't even rolled it out of the garage yet to see if it does figure 8's all by itself, and its scrap ? !!!?

"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"

The OP suggests his frame is distorted 5 degrees, which means after repair tubes will have elongated by 10 degrees. This amount of elongation in an area of the frame which is not highly stressed is something which isnt ideal, but not likely to cause major problems.

However in the relation to tubes adjacent to the steering head area, on a frame which is relatively weak anyway, the safety of the said frame is compromised to such an extent that most pro frame builders would advise it was scrap.

You are unbelievable.

No featherbed (factory featherbed) was 27 degrees, so talk of pulling it to 27 degrees or scrapping it, without having a good frame repairer look at is is just nonsense.

And any good frame repairer should be able to tweak it (a degree or 2 at most ?)(or more if required) without any harm whatsoever. This frame was HOT when it was welded up, and subsequent heatings done properly will return it to perfect working safe order. Frame repairers do it all the time. Check out the annealed strength of mild steel versus plain ole mild steel - and report back...

Do you own anything that has been repaired ? In their day, motorcyclists threw away NOTHING, everything was repaired if possible. I've several earlier Nortons that have broken or bent their frame, repair is perfectly straightforward and routine - the factory advised how to do this back then. Nortons lugged frames were famous for breaking or cracking, Nortons needed the featherbed to bail them out of frame breakage hell...

Cheers,

"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 guess the OP and Maidstone Motoliner the people he has asked about repairs are both wrong then? If this is the case the perhaps you would be good enough to provide the correct information, as your posts here seem to suggest you see yourself as an experienced frame builder, as well as having an in depth knowledge of the effect of tubing being bent well beyond its limits of elongation?

Carbonfibre said:

The Featherbed frame is inherently weak, as there are long runs of tube which are not supported and have no cross bracing of any kind. However they were a step forward from the hearth brazed and lugged frames commonly used in the British motorcycle industry, as they could be produced faster and more cheaply.

Annealing ms tube will weaken it significantly , and greatly increase the chances of bending in future...............but if anyone wants to take a chance on trying to repair a scrap frame rather than buying a new one, its really up to them, but personally I would rather opt for a new frame if major damage involving bending far over the elongation limits of tube was involved.

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I suspect you're trying to be colourful and controversial by saying that a well thought of frame is "weak."

Interesting that the weak parts identified in your posts have now moved from the swingarm and headstock, to meet up at the "long tubes." What problem, exactly, is caused this awful lack of cross tubes under the engine? What is going on down there that should be braced against? Why does nobody seem to think it's worthwhile to add these cross braces? It wouldn't be difficult.

Heating and bending mild steel is pretty much standard practice in every industry. Or do you not think that's true?

I think you should stop posting unhelpful and wrong advice on forums.