Weaving and general road manners

David,

No, the bike should be good until it tops out.

Are the tyres fitted correctly, ie radially and square on the rims

Are the iso's fitted the right way around, if they are vernier they need to be front = adjuster on right, rear = adjuster on left

Are the wheels fitted correctly with the correct spacers.

Check some more, you will find out why. 

Put them on the hardest setting but also make sure they actually work. If the damping has gone, the handling will go with it.

My 850 Mk3 Commando would shake its head decelerating through 30 mph but was great at speed.

Do you have the same section tyres front and back? They can prefer a narrower section on the front.

Are the head bearings too tight?  You do say "they are as they should be" - but what should they be?  They were (usually?) fitted with pairs of ball bearings, but some think they can "improve" them by using tapered rollers.  My Dommie felt unsafe at speed when the taper rollers were too tight.

Check the headsteady, the 3 allens clamping it to the head, the bolts for the sideplates and condition of the rubber buffers. Check the play in the swingarm, both the spindle fit in the bushes and the spindle fit in the cradle. Consider Kegler clamps for the cradle to stop the swingarm spindle wallowing out the hole in the cradle.

https://www.accessnorton.com/NortonCommando/heinz-kegler-clamps.15974/

No David, my dear old Mk2A 750 is as steady as a rock up to about 75, (when my courage runs out).

When I bought the bike 25 years ago the handling was abysmal, certainly compared to my beautiful 99. Over a period of time everything was cured, which included the three following mods: Norvil headsteady, (huge difference), Mick Hemmings verniers, set at 3mm gap, to replace the worn out shims, new s/arm spindle and bushes, with two securing nuts.

I am a bit surprised you got throught the MOT, when they were required, as a good tester who knows his stuff can usually identify something that is not quite right. In my case one test years ago my local chap pointed out that the big gearbox adjusting nut was loose, which it was, but I had not noticed, which explained why it had started to weave a bit on bends.

Owning a Mk2A is a challenge, I can tell you, but it is great when it is going well.

Andy Bone

A number of Commando faults feel more 'dynamic' than on more rigid machines. Everything does have to be right for the isolastic system to work and not amplify faults.

I'd echo the need to look closely at the head steady.  Wheel a Commando around with fuel tank and steady off and you'll see just how crucial this triangulation is. The engine (and rear wheel) are able to move dramatically out of line with the headstock, just by turning the bars at walking pace and allowing the weight of the machine to transfer.

My preference is for the rose joint type of steady, but the standard type shouldn't be causing the problems that you describe.

Have the wheels of the bike been rebuilt ? In my experience, one of the most common faults is caused by rim offset. The Commando disc front wheel was problematical to align at the factory and very few wheel builders manage to get the disc side spokes to stand almost vertically, as they should.

It's surprisingly difficult to see this if using different width rims and / or tyres. Have you measured the offset of the rim from the fork leg on each side ? If the front wheel is offset but 'in line', the steering will be continually trying to correct itself.

Check they are the correct length first. 

I would definitely get the wheels balanced. I recently had Avon road runners fitted to my commando and was quite surprised at the amount of weight needed to balance the rear tyre. Handling does seem more stable at speed after this. I am told that front wheel balancing is less important. My other advice is change one thing at a time and test the result. Otherwise you end up going in circles - figuratively speaking!

Nice looking bike by the way.

Steve, I believe you have it the wrong way round. Any bike I have ridden without balancing the front wheel has been like riding a pneumatic drill when up to speed. 

Commando's may be sensitive to rear balance, especially if the 'security' bolt assembly is still fitted, as that adds a LOT of weight that would need to be balanced out, but at normal road speeds rear wheel balance is not normally an issue unless, as said above, it is massively out.

For the original poster, I read an article a couple of years ago,- I'm sure it was in the  Roadholder, - about 'the worlds straightest commando', or something like that, where the writer went into a deep dive in getting his bike to handle as it was supposed to. Suggest it is worth a search for it.

Regards, George. 

Static balance should be fine. Dynamic balance is for wider wheels.

... you need any modifications to the original setup but the crucial areas to look at in my experience are isolastic clearance (done properly with the weight of the bike off them), steering head bearings and swinging arm bushes. My second Commando which I had for 20 years and 50,000 miles or so never gave me a moment's concern regarding handling.

You don't need to do the isolastics "up tight" but you do need .005" as near as possible clearance.

Something of a "bitsa" you have there...

Anyway, please don't lock up your isolastics, you will break something. Adjust them as per the manual.

Commandos are strange bikes that are very, very easy to turn into evil-handling nightmares. And at the same time they can tolerate 'looseness' is all the things you read about needing to be this way or that. Often you will change just one thing, e.g. a front tyre, and it will go from one extreme to the other. best advice is to find someone local to you who has a Commando or two in their shed and will take a look at it for you - whereabouts are you?

What I will echo from others' comments is that no, the bad handling you are experiencing is far from the best you can expect. And without any special bits a standard Commando will easily out-handle a Jota.

David,

You said that wheel alignment is correct to the best of your knowledge - how did you check it? It is quite easy with some methods, e.g. string, to get a misleading result.

Andy  

George, I think this is the article you mentioned, I found it somewhere on't interweb about 4 years ago, but the original dates back to 1998.

... news. I seem to remember reading (in the Commando Service Notes?) that lighter riders sometimes experienced weave. At 110 kg it's never been a problem for me.

Get a Feather-bed.

.. told then.....

Who needs a featherbed anyway. My plunger garden gate ES2 handles like a dream......

It would be worth checking the right length shocks are fitted, they should be 12.9" centre of eye to centre of eye fully extended. I run with lowest preload solo and have no weaving issues, could be 12.5" are fitted and hence the extra preload needed. Adding preload does not change the spring rate just raises the rear of the bike.

David, it is well worth getting the front wheel balanced,  I gave up fitting my own tyres years ago,  apart from trials etc, as at high speed it really matters. 

Also try adjusting tyre pressures to suit your weight and riding position. Sitting on a Roadster is very different from an Interstate coz your weight is in a different place and as you found out shock pre load affects it too. 

I have recently fitted a pair of Falcon shocks and the improvement over say Hagons has been remarkable.

As yet no-one has mentioned oil in the Roadholder forks. If one side has less oil than the other, they are underfilled or overfilled or the wrong weight of oil is used, weaving is a likely outcome. I suggest sae 20.  While you are at it Kev Feltoe's modification described in Roadholder recently will facilitate future fork oil changes.

Just wondering if you would be better off with a 100/90 on the front of an 850.