Isolastic Centering?

acotrel said:
Many things probably depend on what you are trying to achieve - better handling or more comfort.
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If you'd actually read through this thread then you'd know.

acotrel said:
Herb Becker modified the isos and got Doug MacRae's bike to handle. When I am faced with a problem, I am never averse to re-engineering.
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It isn't about handling but reducing "excessive vibration". Once again this is not about you so STAY ON TOPIC.
 
seattle##gs said:
Have you loosened the top GB mounting bolt and see if the cradle will spring back a little?
I have seen several Nortons where the owners have left out the washer/spacer (3/16" I believe). Not unusual. Loosen the three mounting bolts.. motor-to-cradle and get enough room to shove in the spacer/washer. Tighten the three bolts and put a straight edge on the cradle, both sides. That should solve this problem.
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Yes that will be checked soon. Though I can't see how having this engine plate distorted would impact the iso alignment, I can always hope fixing the missing washer also fixes the iso issue...
 
It probably won't but it needs to be done anyway and, cross your fingers, it may help with the first problem.
 
Ok got a spare rear axle washer, 0.160" thick, btwn the GB drive side lug and inner side of cradle plate. Took a lot of messing around finding a way to spread the bowed in plates. Prying didn't give enough gap. Ultimately, I fashioned a jack screw arrangement consisting of a 2-1/2" full thread bolt, a nut, washer and a suitable length socket. Winding out the botl while holding the nut against washer/socket expanded overall length and ultimately got the plates pushed apart. Not easy, took a few hours messing, but its all in and lined up. Will go through primary chain tension adjusting, torquing all plate & gb mount bolts and re-check iso gaps tomorrow.
 
First test ride. No real difference in vibration level after fitting missing GB spacer. Oh well, worth the try I guess.
 
Tornado, when you say you have ‘excessive‘ vibrations, what are you comparing against to conclude that?

Can you tell us when the problem first became apparent? Has it always done this? Or did it start doing it recently? Does that coincide with anything else that was done at the same time?

The fact you have cradle alignment issues as you describe, and the fact that your top spacer was missing and the cradle is distorted, seems too related to dismiss just yet IMHO. I would suggest undoing a lot more, maybe even removing the gearbox etc and looking as closely as you can for further distortion.
 
Tornado said:
Though I can't see how having this engine plate distorted would impact the iso alignment, I can always hope fixing the missing washer also fixes the iso issue...
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As I’m looking at this in my minds eye, that missing spacer would bow in the left hand plate. That bow is then effectively acting as a spring, that could it be trying to pull the cradle over one way or another depending on what it’s levering against?

I would also ask, is it correct to assume that only the left hand plate got bowed? Could the RH plate also get pulled in and distorted, further complicating things?

When you replace that missing spacer, unless you have identified and straightened ALL distortion PERFECTLY, then the issue of the distortion pulling things over probably remains, in fact would likely be made worse by the addition of the spacer if some distortion remains.

So, in summary, I would personally be thinking that the missing spacer - distorted cradle - high vibration topics are all linked.

I know Commandos are rather crude by modern standards, but to function as intended, that whole engine / cradle / ISOs / frame relationship needs pretty good alignment IMHO.
 
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I see the rear iso unit like as a pendulum pivot point that has been brought to rest with the aid of rubber mounting and including the rear tyre/suspension...so it don't take much to throw it out of skelter....
 
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baz said:
How is the spacer missing?
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Well it isn't missing presently. How it came to be missing previously is not known. I've never had GB out. So either missing when I acquired bike 5 yrs ago or was left out when a complete tear down was done 1.5 yrs ago at a "pro" shop. This is also when new rear iso's went in (sourced from Walridge in Ontario, unknown original maker so could be too hard a compound).

Previous to that work, bike did have fair amount of vibes, but more in line with what others report, maxing out around 2500 and dropping off significantly by 3k.

Since rear iso replacement, vibs are pretty much across all rpms. Mirrors shake enough to blur images. Plus, I have broken/sheared in half three license plate brackets in the past 12 months.
 
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Fast Eddie said:
As I’m looking at this in my minds eye, that missing spacer would bow in the left hand plate. That bow is then effectively acting as a spring, that could it be trying to pull the cradle over one way or another depending on what it’s levering against?

I would also ask, is it correct to assume that only the left hand plate got bowed? Could the RH plate also get pulled in and distorted, further complicating things?

When you replace that missing spacer, unless you have identified and straightened ALL distortion PERFECTLY, then the issue of the distortion pulling things over probably remains, in fact would likely be made worse by the addition of the spacer if some distortion remains.

So, in summary, I would personally be thinking that the missing spacer - distorted cradle - high vibration topics are all linked.

I know Commandos are rather crude by modern standards, but to function as intended, that whole engine / cradle / ISOs / frame relationship needs pretty good alignment IMHO.
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With missing spacer, LH plate was bowed as light could pass between a straight edge and outside of plate. With spacer replaced, light no longer passes. Yes the RH plate would also bow in some amount. This would cause overall position of Gb to shift slightly to LH side. And it explains a slight chain scuffing sound from front sprocket and traces of alu dust appearing on chain after long rides. That sound has now gone with spacer back in.

What I think may be happening is rear iso's too hard and maybe not properely centered in the cradle tube, putting cradle off center towards RH at rear. This makes setting the gap equally Left/right
not possible, Right side can be set at 10 thou, but left will then be 20 thou.
 
It's going to be a pain but I'm guessing you will need to pull the whole lot out in the end and probably change the rubbers if you can rule out misalignment
With anything more than an 8thou gap front and rear all vibes should be gone by around 2500 rpm
 
Other thing I'm contemplating, moving my Hemmings adjuster over to the left side instead of the right. I placed in on the right b/c it just seemed to give easier access when trying to fit the fiddly little grub screws in place. But if my issue is excess gap on left side iso end, having the adjuster there should let me set it to take up that excess, making it even with right side. Maybe there is a reason why MKIII vernier kits are installed with adjuster to the left side at rear? Different dimension on left vs right frame mount point to centerline?
It looks like it will be a tough struggle to fit the grub screws with the primary/ign/stator wiring all impinging in that area.
 
Tornado said:
Maybe there is a reason why MKIII vernier kits are installed with adjuster to the left side at rear?
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It's more accessible on the left due to the Mk3 battery being positioned across the frame, allowing the Mk3 tray 'floor' to be cut back (where the feeler gauge is) for better access although with the plastic airbox in position, I expect it's still awkward.
Isolastic Centering?

Tornado said:
Different dimension on left vs right frame mount point to centerline?
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The offset is built into the cradle the same as pre-Mk3 cradles.

The Mk3 rear vernier adjuster and fixed abutment are (approximately) equal in width, therefore, (approximately) the same as the two pre-Mk3 rear '43' collars.

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