Rear cradle spacing in frame

[zotz]

Many moons ago when I built my 1970 Commando from a basket case I opted to change the ISO's to a verneer set up with a rod link head steady. I ordered a MKIII conversion from Les Emery. After installation I found the rear unit to be narrower than the frame width so not knowing any better at the time and dealing with a basket case I made up spacers to account for the gap. Thinking everything should be centered I put a .050" spacer on the drive side and a .150" spacer on the timing side. I have driven it that way ever since. The ISO system has never worked as well as it should and I would like to deal with that. I know the engine is supposed to be offset in the frame 3/16 - 1/4" depending on who you talk to. If I shift all the spacers to the drive side it will get me close to the proper offset. I just wanted to throw this out there and verify that yes the cradle should sit 1/4" closer to the frame on the timing side.

 

[hybridracer]

The engine, gearbox, engine/gearbox plates, swinging arm, rear hub, sprocket and brake are all offset 3/16” left of the frame centre line.
The frame is symmetrical therefore the isolastic assembly’s are offset 3/16” to the right on the engine/gearbox plates.
The rear wheel rim is offset 3/16” to the right to bring the tyre into line with the frame centre line and front wheel .

 

[L.A.B.]

I just wanted to throw this out there and verify that yes the cradle should sit 1/4" closer to the frame on the timing side.

As hybridracer said the cradle should be (1/8" - 3/16") closer to the drive side.

 

[o0norton0o]

The engine, gearbox, engine/gearbox plates, swinging arm, rear hub, sprocket and brake are all offset 3/16” left of the frame centre line.
The frame is symmetrical therefore the isolastic assembly’s are offset 3/16” to the right on the engine/gearbox plates.
The rear wheel rim is offset 3/16” to the right to bring the tyre into line with the frame centre line and front wheel .

This sounds wrong or it's worded oddly....

If the engine mounts on the frame are offset 3/16" to the left of frame center, and the isolastic offset is 3/16" to the right then there needs to be another asymetry to the left, IF the rim is also offset from the hub another 3/16" to the right... Could there be a 3/16" offset to the left in the shape of the swingarm of hub assembly??? Otherwise your math doesn't add up,... or I am misunderstanding the way you've worded it.... LAB hasn't corrected you,.... so I must be mistaken... but how?

 

[L.A.B.]

The front of the swingarm is offset to the left to fit the cradle but the axle plates are in line with the frame or the shocks would lean over so the swingarm isn't symmetrical.

 

[L.A.B.]

​

Post in thread 'Rear wheel offset'

Aug 26, 2009

LAB, I think it was you that told us the MK3 tubes were not symmetrical. The 750 and 850 arms I've seen were all symmetrical. Since the lower fixings are wider spaced than the top they splay out at the bottom anyway but the RH is more vertical on mine than the right, measured with the bike level (9" spirit level on the springs). Not totally accurate but there is a definite difference.

Yes, my own findings were based on measurements taken from a spare unused MkIII swinging arm.

But I just can't believe the factory would have overlooked or dismissed the fact that the cradle offset...

• L.A.B.

Norton Owners Club of NSW - Commando Wheel Offset

Post date: Dec 25, 2011 12:40:45 PM

www.nocnsw.org.au

From the UK Norton Website:​

Commando wheel offset - the definitive answer

I have the definitive answer as to what is offset, how much, and which way!

I set up a 1973 850 on the frame table and verified it was straight. I then put together a dummy engine and installed it with new isolastics, new washers, Hemmings adjusters, and a Norvil head steady. I put both adjusters on the left side, checked the swinging arm in my fixture and then installed it in the frame. I took all the play out of the adjusters and started measuring:-

The frame is symmetrical

The engine/gearbox cradle is offset 1/8" to the left.

The swinging arm is offset 1/8" to the right so the axle pads end up centred in the frame

I then installed the rear wheel:-

The spoke flanges are offset 1/8" to the left as mounted in the arm, so the rim is laced off 1/8" to the right to put the tyre in the centre

The centre of the rim is 3.3/8" from a straight edge laid across the brake drum (not the backing plate

 

[zotz]

OK, thanks for taking the time to answer my question. I went back into one of my older manuals and found a drawing of older shim type ISO showing front and rear offset to the frame and was able to extrapolate that to real size. Issue I have now is I don't have room to move the cradle to the left any farther other than flipping the rear ISO assembly 180 deg so that the adjuster is on the right. Also my rear wheel already sits to the left of the centre line looking at it from the rear and shifting everything left will make it worse. (yes the rear wheel has the proper offset to it). Also the rear shocks don't look skewed at all. No handling issues and it tracks straight with my hands off the bars. Just a bit more vibes than it should have. Hmmm, need to decide whether I want to go down this rabbit hole or not.

 

[L.A.B.]

Issue I have now is I don't have room to move the cradle to the left any farther other than flipping the rear ISO assembly 180 deg so that the adjuster is on the right.

I don't see how that should make any difference as the vernier adjuster and the fixed abutment should be approximately the same length.

Andover Norton - FRONT ISOLASTIC ADJUSTER COLLAR R/H (VERNIER MK3) - 06.4665

FRONT ISOLASTIC ADJUSTER COLLAR R/H (VERNIER MK3)

andover-norton.co.uk

Front and rear Mk3 but not front pre-Mk3 conversion.

Andover Norton - REAR ISOLASTIC ABUTMENT - 06.5518

REAR ISOLASTIC ABUTMENT

andover-norton.co.uk

 

[zotz]

I don't see how that should make any difference as the vernier adjuster and the fixed abutment should be approximately the same length.

Andover Norton - FRONT ISOLASTIC ADJUSTER COLLAR R/H (VERNIER MK3) - 06.4665

FRONT ISOLASTIC ADJUSTER COLLAR R/H (VERNIER MK3)

andover-norton.co.uk

Front and rear Mk3 but not front pre-Mk3 conversion.

Andover Norton - REAR ISOLASTIC ABUTMENT - 06.5518

REAR ISOLASTIC ABUTMENT

andover-norton.co.uk

You're right it shouldn't but as mentioned this iso unit appears to be somewhat of an odd ball and is .200" short requiring spacers to make it fit in the frame. The abutment end appears to be visually shorter than the adjuster end. It's an old unit at least 15 years old. Curiouser and curiouser.

 

[zotz]

That pic of the rear abutment piece doesn't look like mine. I don't have that large beveled area.

 

[L.A.B.]

Here's an original. It varies slightly but is 0.893" - 0.90 thick.


Did you measure the frame between the plates which should be between 221.99 and 222.50mm.

 

[L.A.B.]

It wouldn't be a front abutment by any chance?
https://andover-norton.co.uk/en/shop-details-2/16540/front-isolastic-abutment-l-h-vernier-mk3-

 

[zotz]

No, kinda tough to measure now with everything assembled. My abutment definately doesn't look like that. It has the same large diameter lower part with the set screw but that whole upper beveled section is missing. I've had to compensate for that with a spacer. Checking my records, the bike was put on the road in 2002 after a long resto so maybe this was some early developmental effort. My thoughts, should I decide to dig into this are to replace the whole unit as the rubbers are now over 20 yrs old and who knows what other dimensions might be messed up.

 

[zotz]

It wouldn't be a front abutment by any chance?
https://andover-norton.co.uk/en/shop-details-2/16540/front-isolastic-abutment-l-h-vernier-mk3-

Interesting. You could be right. Maybe they sent a mis matched part and me not knowing assembled it like that. Good call.

 

[baz]

OK, thanks for taking the time to answer my question. I went back into one of my older manuals and found a drawing of older shim type ISO showing front and rear offset to the frame and was able to extrapolate that to real size. Issue I have now is I don't have room to move the cradle to the left any farther other than flipping the rear ISO assembly 180 deg so that the adjuster is on the right. Also my rear wheel already sits to the left of the centre line looking at it from the rear and shifting everything left will make it worse. (yes the rear wheel has the proper offset to it). Also the rear shocks don't look skewed at all. No handling issues and it tracks straight with my hands off the bars. Just a bit more vibes than it should have. Hmmm, need to decide whether I want to go down this rabbit hole or not.

If it handles well and runs straight I wouldn't alter anything to do with the setup
If your issue is with vibration then it's probably the rubber compound
Unfortunately lez does not care what he sells or where it's sourced from and I can guarantee if you contact him he'll say you haven't assembled it properly