When Norton flipped the Mk2 disc to the left side (317xxx)...

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Going to check for that drift on my MK3 today.
I've switched the rotor to the right side, but it's the lighterthan stock Madass rotor.

Glen
 
worntorn said:
Going to check for that drift on my MK3 today.
I've switched the rotor to the right side, but it's the lighterthan stock Madass rotor.

Glen
Click to expand...
Never thought to check that. I fitted a lightened disc this winter I'll have to try hands off and see if its improved.
 
L.A.B. said:
There have been a few reports that late Mk2/2As had the disc on the left, which Peter Henshaw has apparently copied from a previous Norton publication (as well as a few other errors!), however, I'm not sure how accurate that original information is, and some other 'facts' in his bible are certainly inaccurate or at least questionable.

Moving the brake would require more than just a change of hub as the front mudguard stay cannot be fitted with the caliper on the left, also the brake hose, rigid pipe and bracket would need to be changed for 'Mk3' items or it would look odd.
The spoke pattern is also different between RH and LH disc wheels so a reversed RH disc wheel isn't too difficult to spot although it's not unusual for the complete front end to have been replaced with a later assembly due to accident damage etc.

Eddie Lawson's straight from the crate '317998' Mk2 with RH disc.
https://www.bonhams.com/auctions/20469/lot/345/

When Norton flipped the Mk2 disc to the left side (317xxx)...
Click to expand...

Off topic I know but this is a very useful photo for checking originality. Even the tach cable run is different to how I have mine at present.
 
thought i read there was also a pulling right tendency discovered in testing, with both front & back discs on the right side
 
84ok said:
thought i read there was also a pulling right tendency discovered in testing, with both front & back discs on the right side
Click to expand...

OK really off topic but its a long held story that the Mk 111 disc was changed to the left side fork because earlier right side disc brake models pulled to the left. I heard of this arguement back in the 1980s - maybe earlier. And my Mk 11 319 *** 850 with the disc on the right certainly pulls hard left if you take your hands off the bars. At low speed I have to hang out like a sidecar passenger to keep it going straight.

BUT and its a big but - Is this the disc location or is it an Italian frame, bad isolastics, bad wheel alignment or any one of the multiple things than can upset a Commando's handling ? I suspect it could be but I cannot prove it - yet !

This southern hemisphere winter I plan to bite the bullet and rebuild my Commando following the "Worlds straightest Commando " So maybe in a few months I can answer the question.

That said Phil Read, when he raced the Matchless (AJS) 650s (actually maybe it was the Norton 650 SS ?) in the Thruxton 500 Production races in the early 1960s, reportedly had the wheel rims offset to equalize the weight distribution down the centre line of the bike. He said this made the bike track true and handle better. But you don't have to be a Phil Read to feel the left hand pull on my bike !!
 
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Fast Eddie said:
What’s the logic behind the pulling to one side phenomenon?
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From what I understand (and my '74 suffers the same fate), having the combined weight of the master cylinder, caliper, and massive rotor all on the same side makes the front end lean quite forcefully to the right, making the bike want to side-step the same way, thus putting you into a left-hand turn. When placing mine on the center stand and pressing down lightly on the back of the seat, the front end will make a beeline to the right every time, and do so with much banging off of the frame stop.
 
Thanks Nater, I see the logic at least.

But... the master cylinder isn’t very heavy is it? If that’s really all it is then people who fit a large-ish steel mirror to only one side would induce the same?
 
Makes me want to torch off the old shoe, go for ride an see which way it goes. I know it pulls to one side but forget which. Im old....Ill try
later in the week.
 
Well, that's the issue - that it drifts left with the disk on the right but with the disc on the left doesn't (allegedly) drift at all. WHY? Obviously, no one here seems to know for sure if the claim is even true, and, if it is, what actually causes it. As I posted earlier, I had a friend with Commando who swapped the disc from right to left on his 74 which - he claims - eliminated the left drift. The Norton owners club posted years ago - back in the '90's, if I remember right, that it eliminates the drift. Also, one has to ask, if it makes no difference, why did the factory move the disc for the Mark III?

Personally, I believe the story that moving the disc eliminates the left drift although I have not swapped mine to see if the "fix" works. I often consider doing it out of curiosity if nothing else- doesn't require anything more than a longer brake line. But the left drift, though quite obvious with hands off, doesn't really present a problem since I never ride with my hands off the bars...except to check for the left drift! ;)

As far as why it should work (if it does) I haven't the foggiest. :(
 
Gyroscopic precession?

Don't most roads have a crown on them? If you drive on the right the bike wants to roll off to the right. More castor/fork angle makes the bike roll off less.
Drive on left bike rolls off to the left?
 
Interesting read.
The forks flopping to the right when unloaded on the center stand makes sense with a little countersteeeinf at work causing the drift.

The road crown theory works in the US, what about the UK and down under?

I always thought they moved it to balance the right side braking of the rear disc. More balanced forces under a panic.
Just a guess but If that was the reason the corrected drift was an accidental benefit.

Since no one really knows why it happens I’ll hypothesize that it is a combo of all the weird drive train / wheel off sets / misalignments that it corrects.

I always thought it looked better behind the fork leg on the right vs that wart hanging off the front on the left.


BTW, regarding balance. I have always maintained that I have felt more balanced pulling the right brake and stepping on the left
And pulling the left clutch and shifting down with the right on the forward motion. Just puts me me in more neutral positions.

Other wise, the shifting and braking forces are on the same side.
Now, back to your regular scheduled program..
 
My 850 (pre MkIII) used to drift left when ridden with no hands - I only did as a test after reading of it on here.
Some time later, after installing new isolastics and an improved headsteady, i tested again out of interest and found the drift is much reduced.
YMMV of course.
 
xbacksideslider said:
Disc on right, drift right, but disc on left and not drift left? Someone please explain this to me.
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I think the logic was that the disc and caliper AND master cylinder are all on the right. The master cylinder can’t be moved, therefore moving the caliper and disc to the opposite side of the master cylinder helps to balance things out.

The master cylinder isn’t very heavy though, hence my comment that a large mirror would have the same / similar effect?
 
Yes, mine will drift left unless the road is seriously cambered to the right. It drifts left in a level parking lot. My other bikes don't exhibit the behavior. Since it is so widely comment upon, I'm personally convinced that some amount of it is "normal," at least on pre-75's. Do folks with Mark IIIs find the same drift?
 
This might be off the wall but I'll throw it out for discussion -

What is the weight distribution of our bikes, right to left?

If the wheels are perfectly aligned but the bike is imbalanced, right to left, the bike will tilt toward the side that has more weight on it and then the bike will run to that side; it will drift, turn slightly, to that side.

This, after all, is how MCs turn. The lean turns the bike more than the steering head angle.

There is a slip angle (or, hysteresis, if you will) between the inside and outside of the contact patch that is created by that tilt. The inside travels farther than the outside, creating a pull across the contact patch which pulls the bike to the outside.
 
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