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
 
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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.
 
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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:
Fitting Jawa engine into featherbed frame


Fitting Jawa engine into featherbed frame


As Paul Dunstall sees it:
Fitting Jawa engine into featherbed frame


As Rob North sees it:
Fitting Jawa engine into featherbed frame


As a heavy equipment rigger sees it:
Fitting Jawa engine into featherbed frame


As a cabinet maker sees it:
Fitting Jawa engine into featherbed frame


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.
 
If I was doing it, I would cut the piece out from between the rails and jack them apart to get the motor to a position where it is similar to a Manx. The centre of gravity affects the handling. If the bike feels light in the front, you will be slower.
 
acotrel said:
If I was doing it, I would cut the piece out from between the rails and jack them apart to get the motor to a position where it is similar to a Manx. The centre of gravity affects the handling. If the bike feels light in the front, you will be slower
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Coming along nicely thanks although a little slow due to work commitments. Engine plates made and frame opened out at bottom to allow the engine to be lower. Handling was excellent with the Norton engine in so I've duplicated the position which also seems to line up with how a Manx engine is positioned.
There is no practical way of taking a head brace from the Jawa motor and it appears that most Jawas in featherbed frames are raced without a brace. For me the steering tube does not look supported without a brace so I've added a removable cross brace between the top frame rails (photo) and at the moment it has a bar to the steering tube although I will change this to have a dominator like alloy plate going back to the cross brace and also triangulating at the front frame cross tube (if that makes sense). When I remake the cross tube to take the alloy plate I will increase the diameter from 3/4" to 1"
The frame is going to have the paint removed in the morning so will be ready for spraying and going back together early January.
I'll post some photos when done.
If anyone is thinking of doing same I have templates that I can copy in card to cut down some of the work.
 

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mdt-son said:
If you are serious about constructing a race bike, you should redesign the frame, making it shorter by cutting the top and lower rails. Featherbed frame geometry is odd at the outset! At least this gives you the opportunity splaying out the lower rails as needed. By cutting the downward tubes below the crossing with the upper rails, you have an ample length of tube to accommodate the change in angles. It goes without saying this has to be carefully planned and executed, preferably using 3D CAD. Tubes are rejoined by using inner tubes in an overlap fashion. Welding or brazing should be outsourced to a professional welder.

- Knut
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A friend of mine built a Triton and cut the top and bottom rails to shorten the motor area. He thought there was too much space for the Triumph T140 motor and he was right. To compensate for shorter wheel base he lengthened the swing arm. I put about 500 miles on it working out the bugs and it handled great. A very well done project.
Unrelated...I worked on a Commando that had the two front down tubes bent and the backbone had a good bow in it. The chaincase was touching the Z plate. It still handled OK even at 60 MPH on the freeway.
 
Hindeed , Crooving a 4 x 2 ( or a 2 x 4 if your American ) and spreading the bottom rails , The straight keepers wih the close fit to the tubes ( 100 X 50 ! ) with a fulcrum ! between .
Simulteaneous appearing safer for maintaining alignment . Presumeably one te theother would have it walking , as vthe memory etc has got muddled . SPREADING individually .

Nevertheless , aving the injun angled to match the down tubes , might get it IN better . Plus the V i b e s are dislocated , that way .

TECNICALLY, id do it SO AS the lower run off the primary is parralel to the lower rail plane . STARTING at the Gear Box / Chain - to swing arm ( cross member clearance there )

On Dirt Roads / pre way , i think the ' Low Center of Gravity ' was more relevant . My ome made Triton , and anothers Home Made NorVin. both had the powertrain higher than anticipated .
Bothe were the better cycles rode , by respective pilots . ROAD / Tarmac . Tho the Triton was good on gravel on trigonics - tikly two up . but thats Triumphs for you . ( swing arm & wheel )

So some plywood plates , rulers , string etc . Put the CHAIN ON , and start / go forward , from there .

Fitting Jawa engine into featherbed frame
 


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