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B33 plunger to rigid conversion

I'm considering converting my plunger rear frame to rigid on my 1948 B33, it does seem a shame cutting it about, anyone out there looking for a plunger frame who has a rigid for a straight swap?

email (option): skywarrior1940@aol.com

Re: B33 plunger to rigid conversion

I would not consider the thought of cutting a frame ,my question is WHY??

Dave J.

email (option): jamfam@dragnet.com.au

Re: B33 plunger to rigid conversion

If you just want a rigid rear end and are not interested in the appearance, you can replace the plunger springs with aluminium spacers. Info from Ian Wright.

You can save a bit on weight that way but it will still be heavier than an original rigid rear end.

You can always return it to standard as it does not involve any cutting.

cheers
Pete

email (option): petercomley@web.de

Re: B33 plunger to rigid conversion

You're unlikely to get a direct swap, plunger for rigid, as the rigid frame is far more sought after...The same applies to M Series models...It appears most peoples idea of the quintessential single from that period has a rigid frame!.....

Either that or there are more people than I thought that appreciate the weight saving....The problem with the plunger is it's a fair bit heavier than the rigid but doesn't handle as well and isn't as comfortable as the swinging arm frame..(which is even heavier)...Ian

email (option): ian@wright52.plus.com

Re: B33 plunger to rigid conversion

Why do you need to cut the frame. Just unbolt the plunger back end and bolt on the ridged if you can find one.

Re: B33 plunger to rigid conversion I like some suspension !!

b33-garden

email (option): jamfam@dragnet.com.au

Re: B33 plunger to rigid conversion I like some suspension !!

I don't dislike the plungers, I've had quite a few B, M and A Series...I even like the headlamp cowling on the later ones!:relaxed: ...If weight is the issue with the B33 some engine tuning can soon cancel that out...Ian

email (option): ian@wright52.plus.com

Re: B33 plunger to rigid conversion I like some suspension !!

I've never ridden a plunger further than up and down the road, but the press at the time saw them as a real step forwards in terms of comfort and roadholding.

We use our machines differently now, but I can't believe that the manufacturers would have increased production costs and complication if they hadn't seen a real benefit...Norton were putting near as damn it 90 mph TT laps in on them before the war so they must have considered that even undamped rear springing was better than none.

Is it simply that they don't respond well to wear and lack of maintenance ?

I do think though that they were the beginning of the end for the classic 1930s simple clean lines.

Re: B33 plunger to rigid conversion I like some suspension !!

There were a number of solutions to the rigid frame before swinging arm was adopted and all had advantages (a limited amount of suspension) and disadvantages (Extra weight and potential handling issues....)

Triumph had the sprung hub, very heavy, little movement and over complicated...

Ariel used the plunger/Anstey link set up which was intended to solve one of the problems of the plain plunger design in that the wheel did not move through an arc around the centreline of the gearbox main shaft (sprocket), or even close to it.It didn't even move through an arc at all. Thus it stretched the rear chain or it was slack depending on the amount of spring compression or rebound at any given point...That is why many modern bikes have the swinging arm pivot cast into the crank case as close to the sprocket centreline as possible...

A neat idea but wear of the small bushes used in the links was rapid and resulted in a lot of wallowing about on fast, long corners...I remember it well from owning a MK2 Square Four...

BSA and others used a simple plunger arrangement...The problem there (at least with the BSA) was that the only thing that stopped the two plunger units acting independently of each other, which allowed the wheel to 'tilt' from side to side under cornering loads, was the stiffness of the rear wheel spindle...Even with the much heavier wheel spindle used the effect was not removed and again, wallowing about on fast, bumpy bends was the result...Just ride a plunger A10 at speed to confirm that one...

I've never ridden a Norton with plunger suspension but I imagine the limitations were similar and it was more the bravery (lunacy) of works riders that produced the results rather that the marvellous handling of the bike...

Proof...?...Everyone adopted swinging arm systems...(but Triumph even failed to get that right..:laughing:)...Ian

email (option): ian@wright52.plus.com

Re: B33 plunger to rigid conversion I like some suspension !!

Hi, thanks for the replies.
No real reason for the conversion other than i find the rigid rear end more aesthetically pleasing! Sure the plungers probably give it a smoother ride, might even cushion out some of those pot holes, but i don't like the look of them, and those chrome covers rub like hell and go rusty in no time!
I recall reading an advertisement for the B33 and the plungers were an added extra at significant cost, boy how things change!
I would just replace the rear end if i found one at a reasonable price, but even then I'm still left with an unwanted plunger rear end. I'm more then qualified to do the cut job, so if no takers in a while on wards with plan B !

email (option): skywarrior1940@aol.com

Re: B33 plunger to rigid conversion I like some suspension !!

Bear in mind the rigid mudguard and toolbox are visually different (if that concerns you...) and the toolbox might not fit the rigid frame...The plunger chain guard and mudguard stays won't fit the rigid frame and the entire rear wheel and spindle assembly are different and not interchangeable....You'll also need the rear brake torque arm...Ian

email (option): ian@wright52.plus.com

Re: B33 plunger to rigid conversion I like some suspension !!

I know plunger bikes get a lot of stick, heavy, look horrid, don't handle etc, and but my experience with a plunger ES2, a couple of garden gate Inters and a pepperpot Manx have been nothing but enjoyable. The handling is fine if everything is unworn and well lubricated, not in the Featherbed league of course but quite acceptable, they are pretty weighty though.
I think Nortons are by far the best looking bikes using plungers, in fact a garden gate Inter, or better still Manx, rates among my favourite looking machines up there with the clubmans Goldie, SS100, Jota etc.
Re the pre war Manx handling I remember reading somewhere that the quick works bikes had the plungers locked solid, they were not stable at really high speed but had to give the illusion of having suspension for sales purposes, it may have been in MCS, possibly written by Titch himself, though I've never heard of anyone actually owning a locked up example.

All the best
Tony

Re: B33 plunger to rigid conversion I like some suspension !!

['I remember reading somewhere that the quick works bikes had the plungers locked solid...']

That's what I've done with a couple of the plunger BSAs I've owned...They definitely handle better and give the rear chain an easier life...
The plunger set up isn't too bad for a road bike, after a while you get used to the wallowing about on long bumpy bends and don't worry about it...With the A10 and the Ariel Square four both have the power and the weight to highlight the weaknesses of the design...All the designs represent a certain period in motorcycle development and show how the first idea often isn't the best one...
Like all things they have their advocates though....I've even got a friend who likes to sing the praises of the Triumph sprung hub which I consider to be an abominable contraption, though that is with the benefit of hind sight...
It probably seemed like a great idea at the time as it provided some rear suspension and it was pretty unusual for any member of the motorcycle press to point out directly the deficiencies of anything, so no one was going to disagree officially:laughing: !!!...Ian

email (option): ian@wright52.plus.com

Re: B33 plunger to rigid conversion I like some suspension !!



Hi Ian, some interesting points I hadn't considered!
Would the entire wheel not be suitable because of the hub rear brake arm fitting? Would the spindle be to short for rigid?
These are the only points i could do with some clarification on please.
Thanks for your help.

email (option): skywarrior1940@aol.com

Re: B33 plunger to rigid conversion I like some suspension !!

I think a rigid frame is much narrower than the plunger frame.
The wheels wont't fit.
If you want to change, you better try to find a rear frame with a wheel.

Re: B33 plunger to rigid conversion I like some suspension !!

Yes, virtually everything is different for the rear wheel assembly..

The rigid wheel has a much smaller diameter wheel spindle (with frame slots to match), taper roller bearings as opposed to ball bearings, a one piece hub, not the splined hub arrangement of the plunger, a different brake plate with a torque arm attachment stud (which the plunger doesn't have) and a deeper 'dish' in the centre of the plate, cam adjusters for wheel adjustment whereas the plunger has bolts etc. etc. etc....

I did fit a splined rear hub from a swinging arm BSA to my rigid 1951 B33 as it makes replacement of the drum/sprocket much easier (the drum/sprocket is riveted to the side of the rigid hub and is not available anyway)and the ball bearings of the splined hub assembly are easy to get and a lot cheaper than the correct taper rollers (saying that it is possible to modify some cheaper roller bearings to work...)

However, to fit that up, I still used a rigid type brake plate which I had to modify slightly, re manufactured all the internal and external hub spacers, made a new spindle and nuts and remade a modified version the rear wheel adjustment cams and frame stops...

If you look closely at the photo of my bike in the earlier post you will see the offside chain adjustment cam on the outside of the frame...They are normally on the inside...Ian

email (option): ian@wright52.plus.com

Re: B33 plunger to rigid conversion I like some suspension !!

Thanks Ian, good to know in advance, straying from standard has many problems mostly unforeseen!
Top looking bike you have there!

email (option): skywarrior1940@aol.com

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