Slipping Pazon rotor and ISOs

This is just an observation really. A while ago at Norton day my bike lost its idle for the second time in as many weeks. Thinking it was just the idle screws backing out (though it had never done this before) I gave them half a turn and restored the 1200 rpm tickover (OK...MK1's with 20,000 mile bodies and brass slides.) Simultaneously, the feel of the engine had changed and the usual vibyness at 3750 to 4250 rpm was was worse, very coarse. It still went ok but didnt feel right. One of the conversations that came up was how different Commandos can feel and there were those with turbine like motors (at high revs), others which went well most of the time but alternated randomly between rough and smooth and those like me with a harsh feel around the 4k mark. Actually there were only 4 of us in the conversation so hardly a proper poll :wink: On my return I pulled the front ISO (Norvil vernier from 7-8 yrs ago) which had been set as normal to 010"/012" or 3.5 adjuster holes out from locked up, so just under half a turn. I pulled the rubbers (very soft but no obvious damage), turned them 90 degrees and refitted them. I usually position the rubbers so there is some clearance between fixed cap and the end cap and tube. This time I nudged the rubbers until the fixed cap just took up all play screwed home and set the adjuster collar 4 holes out (1/2turn). 4 holes is Norvil's way and no way 10 thou, more like 012"/014" with 25lbs/ft torque on the bolt. Whats this ramble got to do with the Pazon you ask, none at all except a timing check revealed it had also slipped 8-9 degrees and was 19 deg at 3000 rpm, 21 deg at 4500rpm, hence the idle speed reduction. The trigger plate had not moved (sharpie marks still aligned) so I'm guessing the rotor had slipped. However it was tight and the bolt would not tighten further without really leaning on the allen key. The net result of all this is that on a 115 mile ride the harshness has all but gone and she pulls like never before even when the timing was spot on. That half a hole on the ISO made and unbelieveable change which I would not have thought likely....and the handling has not suffered noticeably. As for the timing I have no explanation as it certainly hasn't run like it did yesterday since it was rebuilt with new rings this winter. Maybe the nicer feel of the engine made it feel faster??

The rotor retaining bolt can be too long, it then bottoms out in the hole in the camshaft giving the impression its holding the rotor firmly in position but it grip is actually light and the rotor moves. I would use a new retaining bolt 1/4" shorter or reduce the length of the current bolt to make sure the rotor stays put in future.

Thanks and good point Kommando. I was thinking the same as it does feel like its bottomed. It is an aluminum rotor after all. Will take another look. Still amazed how well its going though

On a slightly different tack, I have the tool for releasing the advance/retard mech from the end of the cam. It's a screw with a long section of plain shank below the thread. It's supposed to bottom out in the cam and push the A/R off the taper. It works for the original Commando cam but the PW3 has a much deeper hole and the shank does not bottom out. I don't think the threads in the PW3 cam go very deep so shortening the screw retaining your trigger sounds like good advice to me.

You know, old bikes always run best just before they blow up!

Cam chain slack?

Dave

Not rising to GPs comment
Cam chain could be but wouldn't the tight top run under power keep it tensioned for proper cam and ign timing. I could understand erratic timing etc but its stable on the timing light. Bolt is also over an inch from bottoming out. Another mystery I guess......

Just a thought. One of your throttle cables sleeves might be damaged or have temporarly slipped from the right position, either at the splitter or at the top of the carb, desynchronizing your carbs badly.
It happened to me 2 weeks ago. Didn't think of that, adjusted quite a few things on the bike, then when I eventually found out what it was, the bike, thanks to the various adjustments done in the meantime, was going better than it ever had... :mrgreen: