commando featherbed

Hi Neil,

I know a chap who did this, he also had the crank balanced for a rigidly mounted engine but it still vibrated too much so he sold it. He only got £5000 for it which would make the value of the rebuilt engine + gearbox and the tidy rolling chassis about £2500 each. Others have had more success using isolastics or rubber mounts. Any Norton twin engine over 650cc rigidly mounted in a featherbed frame is going to vibrate some what and as such are far more suited to isolastic mounting IE Commando. A 650cc featherbed is a fine machine anyway.

Regards, Al.

Norty.pdf

850 in my old 88 frame. Yeah, it tingled a bit, but then- they all do that, dont they?!

To be honest, I dont really see the point of taking a perfectly good featherbed, putting a bigger Atlas engine in, then hold it together with rubber bands. If the vibration is an issue, just get a Commando in the first place, and stop ****ing about...Its like moving to the countryside, then complaining about the smell of the pigs**t....

A Featherlastic is definitely the way to go. Bob Katz sent me some pics from the US regarding the mounts. See attached Pic. The mounts were made by Randy Ullery. He stated that the chain guide was critical so I enclose a pic of that too.

Peter

And another thing: mounting a Commando engine upright like I did, the Norton script on the timing cover slopes upward. So you mount the engine inclined as per Commando (I forget the angle- is it 15 degrees?). that solves the look of the timing cover, only now the barrels are not parallel to the downtubes, cos the Slimline has a different headstock angle to the Commandos...

Rant over.

Interesting lash-up. I would cut and shut the Commando plates and use Silentblock car bushes from a car suspension. Landrover parts spring to mind. Done it once, use stiff bushes to stop the chain pulling too much. The pictures show a bad top mount which will shear those small bolts. You want to lift the plate up higher so that the mounting goes through it. The chain guide gives me the shudders. What is it for? When the chain breaks and wraps round it I reckon at seventy MPH you should get across the Grand Canyon. The first Norton in space, eat your heart out Elon!

For the anti vibration setup used in the dying days at Meriden they used slientblocs from the Triumph 2000 car engine at the bottom of the engine. 

Having had my knuckles soundly rapped by Neil H, in my roundabout way I was defending the featherbed design- admittedly from a point of ignorance of never having the opportunity to ride a Commando. I do accept that the Proddie Racers in the hands of Mick Hemmings and the like are excellent handling bikes when well set up, as is evident from TTs etc.

I cant recall seeing a challenging Dommie v Commando Head to Head, but I’m sure it would make "interesting" reading!

To come back to my point, to me it makes no sense for the structural dynamics of the featherbed frame, from the brilliant headstock configuration, back to the swingarm, with its excellent resistance to twist and flex, to be somehow compromised by rubber interfering with the swingarm mount (and yes I know the silentbloc bushes are part rubber)

I fully endorse the idea of isolating the engine, and I’m intrigued by John’s Meriden setup above. With a frame-mounted swingarm and gearbox - to ensure final drive chain alignment- and an isolated engine driving by belt to accommodate the relative flexing motion between it and the gearbox, I think that is an excellent concept for development. Just needs rubber chaincases too I guess!

PS My bikes may have smoked a bit, but I never did-although I fancy a John Player right now;-)

I’m pretty sure primary belt drive as currently used on bikes would not survive just engine rubber mounting. The late Triumph had whole engine and partial swing arm rubber mounted from the drawing shown.

    Featherbed v. Commando: having owned and ridden both extensively, they are different, but not hugely so, so it comes down to personal opinions in any comparison. To me, the vibration isolation is the key winning advantage for actual riding experience.

My 750 Commando F/bed is for sale in the latest RH. Electric start and all. Give me a ring.

Tony