Fitting Jawa engine into featherbed frame

t ingermanson said:

If it were me, I'd get in place all the other components that might create an interference, i.e., oil tank, intake/carb/bellmouth, primary gear or pulley, etc. From there, see what fits where. Often times these decisions make themselves.

I'd also be inclined to spread the lower rails to make room, as Knut mentioned, by cutting the front cross brace, spreading that front lower corner, and replacing or patching the cross brace. Less fiddly than denting.

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I’ve done this with all ancillary components in place and also foumd several photos of Jawa engines only using the crankcase top lug with an extra mounting point near the bottom bend of the frame so that’s the way I’ll go. Engine position where it should be.
I found the photos on Facebook Featherbed Specials and have put the question re where to mount the head brace with the answer from two people that they don’t use one - one is a road bike and one race. This seems crazy as the steering head needs support. I’m hoping someone racing will get back to me with information. Apparently there a number of these bikes raced in Australia but it’s difficult finding someone to talk to.
I’m thinking maybe a removable cross brace across the top frame rails above the cam box?

Richard Tool said:

I would be interested in hearing ( in layman’s terms ) your thoughts on the oddities of Featherbed frame geometry. Seems to me ( an amateur) that it is one of the most successful and long lived frame designs in history. Keep it simple as I am the son of a Norwegian woman …

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Richard, my main objection to the frame design is length of space set aside for the powerplant. A shorter frame yields a stiffer and lighter frame! Secondly, Norton placed the gearbox far ahead of the swinging arm's pivot, which causes an interference problem (chain rubbing the S/A). Normal design practice and common sense dictates the final drive shaft (=sleeve gear) to be placed as close to the S/A pivot as possible, ideally at the pivot point itself. Thirdly, by designing a wider cradle, the engine lump can be placed lower between the rails, lowering the CoG and improving handling.
One of the strengths of the Featherbed frame is its forward location of the CoG, putting more weight on the front end, which benefits resisting the drifting tendency in curves. By shortening the spatial parallelogram-like structure and lengthening the S/A, the same effect can be achieved.
By the time the slimline frame came about, the Featherbed frame had outlived itself, as the advent of Seeley, Rickman and other novel frame designs of the early 60's demonstrated.

- Knut

Tusen takk Knut !

Charkmandler said:

I’ve done this with all ancillary components in place and also foumd several photos of Jawa engines only using the crankcase top lug with an extra mounting point near the bottom bend of the frame so that’s the way I’ll go. Engine position where it should be.
I found the photos on Facebook Featherbed Specials and have put the question re where to mount the head brace with the answer from two people that they don’t use one - one is a road bike and one race. This seems crazy as the steering head needs support. I’m hoping someone racing will get back to me with information. Apparently there a number of these bikes raced in Australia but it’s difficult finding someone to talk to.
I’m thinking maybe a removable cross brace across the top frame rails above the cam box?

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Yes, I’d go with a removable cross brace. Probably a nice flat plate that I’d find some way of using the 6mm cam cover screws to secure it to.

Then add a diagonal to the steering head.

the lowboy frame, designed for the 500 twin, has much wider splayed tubes under the engine. Andover did make a replica a couple of years ago, but now only sell various brackets for it.

jan nelder said:

the lowboy frame, designed for the 500 twin, has much wider splayed tubes under the engine. Andover did make a replica a couple of years ago, but now only sell various brackets for it.

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The “lowboy” frame was an experiment in reducing the frontal area of the works Manx Nortons and had no connection with the 500 twin. The Domiracer frame did not have a name other than being the Domiracer frame. It always made Doug Hele annoyed when someone used the name lowboy in connection with his Domiracer.

Andover Norton calls it the Lowboy, so we'll let them take the fall for everyone else calling it that.

As a very stern looking Doug Hele sees it:




As Paul Dunstall sees it:


As Rob North sees it:


As a heavy equipment rigger sees it:


As a cabinet maker sees it:


Oh dear, poor Doug must have his knickers very much bunched! Rest in peace, Sweet Doug. Don't let the unwashed heathens drag you down.

jan nelder said:

the lowboy frame, designed for the 500 twin, has much wider splayed tubes under the engine. Andover did make a replica a couple of years ago, but now only sell various brackets for it.

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so it was the Domiracer frame, the above applies to it .