Feather...lastic

Previously wrote:

Dear All,

I just came across an article on the Web describing how people in the USAlike Bob Cox fitted a Commando engine into a F'bed whilst keeping the vibrations under control through isolastic mounts (hence no need to rebalance the Commando crankshaft).

I would like to do the same and am looking for the isolastic engine-gearbox plates and head-steady which are very specific and not easy to design andmake I imagine.

I've left a mail to Mike Haracourt who did that for Bob.

Have you heard of other examples in the UK, or of a source for those cradles and head-steady ?

Many thanks too for your global thoughts and recommendations about the idea.

Laurent

Have a look at Ron Fraturrelli's web site www.nortoncommando.com as Ron has put a Commando engine into a featherbed frame with rubber mountings.

I am starting featherlastic build based on a Slimline frame, and just found this old thread. 
  Having built two norton feet forward specials from scratch, the special metalwork is no problem . 
   The main decision is : 1. Swingarm bolted to frame in usual position or 2.Commando swingarm on adapted Commando rear engine cradle. Either will work, and the rear wheel ends up in much the same place.
    Option two reduces problems with long chain run, and chain tension pulling on Isos, and will require modding the frame to allow for width of swingarm as it passes rearwards past rear vertical frame loop, which is simple to do.
    Option one maintains the more rigid frame/swing arm combo, and I think will require a narrow Iso-type extra lateral mount near bottom-rear corner of rear cradle. ( this could also feature in option two if desired)
   I currently have crankcases/gearbox/ rear Commando cradle and frame loosely assembled for design purposes.
    I have read most of what I can find on building them, but very little about riding impressions etc, so does anyone have experience of building / riding these please?

Interesting project. Long ago I put a re balanced 750 Commando engine in my Atlas and did a few thousand miles upsetting traffic cops, touring etc. Never saw any sense in the Triton idea.

Still vibrated things off and it made me promise to buy a Commando one day, especially after seeing a new Mk3 in 1975.
Too expensive but the best way to have a smooth reliable, large capacity Featherbed bike is put a 4 cylinder engine in it as Rex McCandless tried back in the old days.

I had plans to fit a solid mounted swingarm in my Mk3 using Silentbloc swingarm bushes and spacer to possibly give a little deflection to the chain. I came to my senses and kept the proven ISO setup. Glad I did, it works perfectly. 

Fitting the complete inclined engine, gearbox, cradle and ISOs assembly (including a Norvil ISO head steady) into the Slimline may be the way to go. 
 

Where is the centre stand fixed? The F bed one comes off the frame in the middle. The Commando? And then there is the spring?

Smarter engineers than me determined that the rear wheel and engine/gearbox needed to be on the same (sub)frame to prevent the chain dissolving. Which means option 1 should be discounted.

And, at the risk of inciting a lynch mob, the Featherbed frame is not really that good. It's reputation comes from the 1950s/60s when the welded construction combined with a low-slung single engine and front forks with some damping put it streets ahead of the competition. It's not structurally efficient, i.e. it needs a lot of metal to make it stiff enough and a twin engine has to sit much higher. The Commando frame is lighter and, properly maintained and setup, will easily out class an Atlas.

Not for me to criticise of course, a special is, well ... special.

Featherbed is a great frame for old school street specials however, plenty of room for mods, durable and close to 50/50 weight distribution depending on engine type. I would say it's probably stronger than a Commando frame which can bend the front downtubes and spine in a relatively low speed front end accident.

I've done both sad to say. The Featherbed bent the forks and wheel same as the Commando but stripping it back to bare metal and checking the complete frame in 2023, nothing else. No cracks, alignment still very good and only old accident damage from the 70s and 80s etc needed repair.
Steel yokes on both are pretty tough, no damage to report. 
 

If you have the swing arm mounted in the isolated Commando cradle, then in a way what you have is a Commando draped in Featherbed tubes for cosmetic reasons.

I've seen "Featherlastic" specials where the steering head bracing formerly provided by the Featherbed head steady has not been replaced.  It looked pretty weak.

I suppose I'd connect the top of the steering head to something further back than the first crossmember.

In 1976 I welded a long 1.25"ø tube from the top of the Atlas steering head back to the short cross member holding the seat pegs.
Welded a frame gusset below the pegs and an additional lug under the new tube, above the existing head steady lug on the front cross member.

Custom head steady bolts up on those two points and the cylinder head to form a much stronger connection. Possibly partly why the steering head wasn't bent or any tubing cracked in the various accidents over the following decades. 
It could also be a convenient mounting point for a Norvil ISO head steady.

The tank already has a tunnel as if the factory intended to do this mod but never did. Shame they didn't fill the gap to provide much needed additional fuel capacity to the miserly 3.5 gal tank.