handling and isolastics

While it is clear that a good head steady and correct isolastic end clearances will improve the commando handling, I went about it a different way.
Back in 76 (I guess I’m showing my age) I took my Norton crankshaft to well known (Sydney, Australia) engineer Claude Cartlege for balancing. While there I discussed the handling problems of the Commando. Claude reckoned that if I did away with the rear isolastics and pivoted the rear iso mount on bushes instead that it would fix the handling problems. (ie the swinging arm would have something solid to mount to . Claude also spoke about how Norton fitted rubber bushes to the swing arm of a Manx which upset the handling, but quickly returned to bronze bushes). He also reckoned that vibration would not be excessive as the front and top rubbers would absorb the vibes.
I then had Claude make up and fit some bronze bushes for the rear mounting and a hardened pivot pin which was the combined length of the rear rubber iso steel centres. The isolastic end caps and shimming procedure remained the same (and I have always shimmed to .010 end clearance). Claude balanced the crank to 53% which I hoped would be right given the new mounting system.
The result was greatly improved handling with no apparent increase in vibration to the rider. The engine did however look as if it was going to jump out of the frame at low revs under load (slipping the clutch up hill in slow traffic ) but smoothed out at normal to high speeds. Obviously there are less rubbers to absorb the vibes so when the vibration of the engine is most intense the engine movement is greater than with the standard set up.
The only problem that I had was in trying to fit the engine/ gearbox assembly to the frame. After attaching the rear, now fitted with bushes, the front engine mount was right over one side of the frame. Clearly there was a small error in the frame or engine plates that was absorbed by the rubber iso’s. I overcame this by slightly elongating the rear frame mounting holes until the front alignment was central in the frame and then I welded up the other side of the elongated mounting holes and file finished them round again.
I lubricated the rear pivots by fitting grease nipples. It would be possible to fit O rings to the pivot shaft and fill the cavity between bushes with oil. Given the very small angle of movement , wear of the bushes or shaft has not been excessive.
I would be interested if any one has done a similar modification

Sounds to me like you need to talk with Jim Schmidt at JS Motorsports. He was talking about solid rear iso mounts a while back to be used in conjunction with his light weight pistons.

Interesting innovation though not original with your crank balancer as this was used in prior old singles with similar success, some were completely fixed at back but frame allowed the front to bounce in rubber ease. For the less innovative like me, I was advised to stuff the rear iso tube full of the large doughnuts and get similar but more silent restraint towards eliminating Cdo antics. Also delays the inevitable sag back there too.

You can't go rigid on the rear isos without addressing the balance factor, which you've done. Good move.

The thickness of the iso end riggings are different front-to-back; they take the adjusters on opposite ends in order to fit properly in the frame.

Kenny Dreer tried harder solid rubber donuts at the back, and filled the iso tube 100%, but the results were't an improvement according to him (yes, he had a complimentary balance factor at the crank). Now that I think of it, maybe he filled BOTH tubes, probably not a good thing... He ended up going to a lower iso which was his final solution with satisfaction as a result.

Mick Hemmings said in an interview in one of the bike mags that he used 5 bushes in the rear iso on his race bike. I tried it and it turned out that there is a reduction in the wild bouncing at low rpm's but it is just as quiet over 2500rpm. Probably no benefit in the handling though. I'd be spooked at the thought of using a solid mount because I don't think the frame, and the tabs in particular are up to it.

Partly form Bob Patton and partly by my own observations and testing of about the world's worse worn out [1/4" gap] isolastics [buddie's not mine] The main motion is both up/dn oscillation at front plus side to side slapping at the front. I saw this side to side slapping action cause the forks to wiggle enough to cause slight leans wobbles back to the rear patch which is what can magnify into defamed hinging. There is also a twisting motions, which can be a real good thing as long as it don't get magnified by the spring backs above.

A more non compliant rear pivot point can't control the real down sides of two sticks though rubber dough nuts no more than griping the pivot of teeter toter can control the kids hopping on the ends.

Add too much rubber area and isolation threshold goes up.

rpaton
I believe the frame is up to the job (although a proper 4" spine frame with a stronger rear engine mounting would be nice). I modified my rear isolastic mount back in 1976 and have done over 60,000 miles since then (not a high mileage for the time frame but its not my only ride). I have not had any problems. I don't think the rear mount should be regarded as solid as the vibes are absorbed through the front and top isolastics (unlike a solid mounted engine). The engine pivots on the rear mount as it vibrates. Virtually no vibes are transmitted through the frame to the rider. The mounting system does give a movement free rear end which eliminated the wobbles that I experienced prior to the modification.
regards ando.

Ando,

60,000mi with no problems pretty much says it all as far as the frame being able to handle it goes. Stabilizing the cradle with regards to tilt is what everybody is trying to do with links and iso's under the trans. Your method has the mechanical advantage of the wide stance of the rear iso working for it. I'm a chicken when it come to concentrating loads on the Commando frame. I guess it's tougher than it looks.

A few years ago at Stafford Classic Bike show there was a late Triumph 650 ' proto type' for sale, it had a pivoted rear mount and a strange Commando style front ISO. The seller said it ran smoothy and handled well, but then he might. Anyhow the mod was very well done and did indeed look factory.

Cash

Personally I feel pretty comfortable relaxed eager for more power to handle smoother/harsher on Patton rear link, Tryee's front link and hobot top link plus Roadholders corrected as designed. To me Cdo fualts are totally solved in Peel's case but always interested to understand why or other ways just as good or better. The weird part is only the ends of Peel are more stable but her hinge still has full range in the middle and I like it! There are at keast 4 rear and front and top links Cdos in the works, most are life time hot shot riders so await their sensations of it.