Welding a solid non-isolastic Commando frame

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Jul 7, 2003
Has anyone tried to transform the rubbery commando frame into a solid frame? I'm a vintage racer, and I'm really hampered by the rubber mounted swingarm. I've considered a Seeley or featherbed frame, but I'm currently thinking of modifying my Commando frame.

Isolastic frame


Not sure how familiar you are with Commandos and their handling. Is handling why you ask about solid mounting the engine?
sloppy versus solid for racing

Hi all,

Yes, handling is the issue. I run my isos tight, and I have a nice Norvil head steady. I've contacted Kenny Augustine about blueprinting the frame too. It's a lot of trouble and expense to do that ($1k-$2k). The result I am sure would be an awesome handling bike for fast street riding.

However, in racing, there are fast transitions, lean angles, throttle use, and high speed dips that are never encountered even in the fastest street riding.

At each track I go to, I find 1 or 2 corners where the forces simply overwhelm the iso mounted frame. These are typically a fast transition from full lean one side to full lean the other side. Knee on the ground to knee on the ground. Usually between 80mph and 120mph. Examples: Turn 10 esses at Buttonwillow, turn 8A/B transition at Sears Point, turn 5 at Thunderhill. If there's a dip in the road (eg. Turn 3A at Sears Point or 6 at Laguna Seca) it's even worse. What I have to do in these turns is be suuuuuper smoooooth and baby the bike and not be WFO on the gas.

Top vintage racers all seem to be running Seeley or Featherbed frames if running Commando motors.

Buying a new frame and shipping to the USA would cost a little bit more than doing the whole isolastic blueprinting job ($2500). But that's not the entire expense as there would be new tank, oiltank, rearsets, etc that would be needed. :twisted:

Thus my though of either rigid mounting the swingarm or rigid mounting the entire engine, gearbox and swingarm. This would of course require changing the balance factor of the crank, but I'm in the middle of a new engine build, so I could do that easily.

If you look at the history of Commando racers from the Norton factory, by 1973 they were running a monocoque chassis (like a modern deltabox) with fuel and oil in the frame. The swingarm was rigidly mounted, and this supposedly was a huge step forward in rigidity and handling. The engine was still isolastically mounted because Denis Poore of Norton insisted upon it to have a link to the iso-mounted Commandos that they were selling for the street.


Well than seems like the fastest and easyest means to this end would be to press fit in some Half inch pieces of lathe turned 6150 into the ends of the iso tubes that have some snug clearance holes for the motor mount studs. This would be best done with the frame blue printing so as to clean up the straightness. I would think that the large tubes of the iso brackets would give in strenth what they take in wieght. You could still run the gatours for the stock look. That will keepem guessing. norbsa
nice idea

That's a nice simple approach, and probably the most affordable. I was thinking of adding lugs midway along the bottom frame so as to have a 3rd mounting point for the cradle.
I hope that you rebalance your motor if you make it a solid mount. I have also heard that a commando frame WILL break from the vibration if you solid mount the motor. this does not sound like a very good idea to me the commando frame is made from a light weight tubing and the swing arm is also not ridged enough.

There are poly bushings that are real stiff. You might try adapting very stiff bushings to see if you could fix the handling and keep the 20 lb frame. I don't know how much the good frames lb out but I bet it's more. An adventure like this alwas costs but poly bushings and several days of carful assem. shouldn't be to stiff. I have no dout that this this frame would give way if soild mounted but there may be room between the pounds and handling to make you able to compete. I would think that finding a fast way around the track might be harder if useing the fast guys with ridged frames as a riding example. You may have to break that mold as well. norbsa Can't win Can't break even Can't quit
breaking the frame

My plan had been
1. rebalance the crank to 80%
2. add stronger engine mounting tabs (the current ones, esp front, are too flimsy and will break)
3. solid mount the swingarm from the frame, not the cradle

I'm still investigating sources for Seeley frames. Roger Titchmarsh never answers his phone and has not faxed me back. Has anyone dealt with Barber Engineering in Norfolk? Any other ideas for sources of Seeley frames?

- Dave
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