Something's bent

T

Tigernut

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Just got my 850 MkII home and onto the lifting bench. Noticed that the rear wheel is tilted at an angle of several degrees when viewed from the rear (top is to the left, bottom to the right). Measured distance to centre of spindle from deck of bench and the right side is approx 17mm higher than the left. It isn't that the centrestand is bent and the whole bike's leaning - the bike is pretty well dead vertical. So the swinging arm at least must be bent. The whole engine/gearbox/swinging arm cradle could be bent but there's no sign of any stress marks when looking around with a light. The main frame looks fine to the eye.

I suppose my questions are, do Commando swinging arms bend easily? Or the cradles? And is there a good place within UK where I can take the whole frame with cradle etc to be checked & straightened? Or, can the main frame be checked by itself? (not sure how practical this is because with T140 frames, the place I've used want the engine or at least crankcases fitted not the same with a Commando). Feeling pretty sick right now!

Can I post photos?
 
Tigernut said:
I suppose my questions are, do Commando swinging arms bend easily?
Click to expand...

They can although the 850 Mk1 and Mk2 swingarm should have two gusset plates that you might want to check are there.

Andover Norton - REINFORCEMENT GUSSET FOR SWING ARM (WELDING REQUIRED) - 06.4540

REINFORCEMENT GUSSET FOR SWING ARM (WELDING REQUIRED)
andover-norton.co.uk

Tigernut said:
Can I post photos?
Click to expand...

Yes, but you either need to become a VIP member to upload directly or use an image hosting website.
 
L.A.B. said:
They can although the 850 Mk1 and Mk2 swingarm should have two gusset plates that you might want to check are there.

Andover Norton - REINFORCEMENT GUSSET FOR SWING ARM (WELDING REQUIRED) - 06.4540

REINFORCEMENT GUSSET FOR SWING ARM (WELDING REQUIRED)
andover-norton.co.uk



Yes, but you either need to become a VIP member to upload directly or use an image hosting website.
Click to expand...
It does have the pair of triangular reinforcement gussets. Thinking about it, the rear wheel's rim is near perfect while the front one has patches of missing chrome. I wonder if the rear wheel was rebuilt / replaced after a crash which caused the twisting? It must take quite some force to cause this kind of twist, I'd have thought? (I'm not used to Nortons at all so please excuse what may be ignorance!)
 
I’ve seen that Verticle alignment issue before.
Could be something is bent, or.
I’ve wondered if long time storage on the side stand could deform the ISO’s.
Is the top of the wheel angling to the Starboard.
 
L.A.B. said:
They can although the 850 Mk1 and Mk2 swingarm should have two gusset plates that you might want to check are there.

Andover Norton - REINFORCEMENT GUSSET FOR SWING ARM (WELDING REQUIRED) - 06.4540

REINFORCEMENT GUSSET FOR SWING ARM (WELDING REQUIRED)
andover-norton.co.uk



Yes, but you either need to become a VIP member to upload directly or use an image hosting website.
Click to expand...
If you use these gussets you will need someone who really knows welding. If you use an average welder that swing arm will warp badly.
 
I have the same issue, 1973 750,while on the center stand. I took the swing arm off and it was straight. New isolastics didn’t make a difference. I followed it while my son rode it and everything looked good, fortunately, so I’m assuming it’s how the center stand is connected to the cradle. The bolt holes are slightly wallowed. I’m not too concerned, just living with it for now.
 
1973x75 said:
I have the same issue, 1973 750,while on the center stand. I took the swing arm off and it was straight. New isolastics didn’t make a difference. I followed it while my son rode it and everything looked good, fortunately, so I’m assuming it’s how the center stand is connected to the cradle. The bolt holes are slightly wallowed. I’m not too concerned, just living with it for now.
Click to expand...
That sounds very encouraging! I'm not used to Commandos so don't know about their peculiarities yet. But I will get if off the centrestand and take another close look.
 
Bent swinging arms on Commandos are unfortunately rather common. My late Mk2 850 was bent about 7 mm. Checked on v blocks.

Usually accompanied by a high speed weave.
 
Could SA be checked with rear wheel off, using a straight edge across the arms at the axle slots?

First guess is you only have the tilting while on centerstand...due to stand pivot wear and or isolastic rubber age deformation.
 
I have welded up Commando swingarms. The mod I do is like the 850 gussets on steroids. I don't think it can be done without warping the swing arm. Therefore: straightening afterwards is a must. I use V blocks on both ends and use a torch to heat up small portions which pull shorter as they cool. When it is all done the pivot axle and the wheel axle should be in the same plane exactly.
 
Thanks all, for the helpful replies. I'm hoping like hell it's just the centrestand. But if not, it's kind of useful to know that bent swinging arms aren't all that uncommon. There are several for sale on Ebay (by which I mean swinging arms, supposedly good - not bent ones)
 
Tigernut said:
There are several for sale on Ebay (by which I mean swinging arms, supposedly good - not bent ones)
Click to expand...

Note there's more than one type.
750 swingarms generally don't have the gussets unless they've been welded in, also there are two types of '850' swingarm, the early type with the longer pivot pin and bushes with end caps secured by a long thin bolt and the later sealed pivot type with a shorter pin and bushes, felts and Welch plugs. These later parts you won't find in the Mk2/2A parts book although they are available. You can fit either type swingarm but you need the correct set of pivot parts.
There's also the 850 Mk3 type swingarm with a box section cross member but it isn't suitable for fitting the drum brake wheel.
Only lubricate either pivot assembly with heavy oil (EP140), not grease.
 
Tigernut said:
Thanks all, for the helpful replies. I'm hoping like hell it's just the centrestand. But if not, it's kind of useful to know that bent swinging arms aren't all that uncommon. There are several for sale on Ebay (by which I mean swinging arms, supposedly good - not bent ones)
Click to expand...
Always thought Norton swing arms were intentionally bent a bit from factory , as welded up new . Anyone know ?
Far more likely to be a different issue , yes wallowed out center stand supports , or yes , collapsing old isolastics , or as I recently discovered , bad old head bearings .
 
Torontonian said:
Always thought Norton swing arms were intentionally bent a bit from factory , as welded up new . Anyone know ?
Far more likely to be a different issue , yes wallowed out center stand supports , or yes , collapsing old isolastics , or as I recently discovered , bad old head bearings .
Click to expand...
Where's that drunken Russian neighbor when you need him?
 
I'm becoming hopeful that it's a case of collapsing old Isolastics. The angle of the rear wheel is what one would expect from the bike being on its side stand for years. Also, it looks (from the contact patch of the side stand) as if the bike has been started on the side stand habitually, which would also tend to push the wheel/swinging arm/cradle in that direction in relation to the frame.

If that's all it is I'll be very relived. I was planning to overhaul the Isolastics anyway (probably replace with the MkIII adjustable type if I can get some)
 
Tigernut said:
I'm becoming hopeful that it's a case of collapsing old Isolastics. The angle of the rear wheel is what one would expect from the bike being on its side stand for years. Also, it looks (from the contact patch of the side stand) as if the bike has been started on the side stand habitually, which would also tend to push the wheel/swinging arm/cradle in that direction in relation to the frame.

If that's all it is I'll be very relived. I was planning to overhaul the Isolastics anyway (probably replace with the MkIII adjustable type if I can get some)
Click to expand...
Tigernut said:
I'm becoming hopeful that it's a case of collapsing old Isolastics. The angle of the rear wheel is what one would expect from the bike being on its side stand for years. Also, it looks (from the contact patch of the side stand) as if the bike has been started on the side stand habitually, which would also tend to push the wheel/swinging arm/cradle in that direction in relation to the frame.

If that's all it is I'll be very relived. I was planning to overhaul the Isolastics anyway (probably replace with the MkIII adjustable type if I can get some)
Click to expand...
Hope is an emotion.


Have a skilled eye look at it.
Easy to see where problems are when a person knows what to look for.

Report back please.
 


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