Cracked Frame

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Ron Hulton

Ron Hulton

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A friend dropped over last night with his nice shiny 1971 Roadster . Shiny enough to see the frame cracked in both down tubes connecting to the rear isolastic mounting gussets . Looking for information to make proper repairs . Thanks in advance , Cracked FrameCracked FrameCracked Frame
 
The cause needs fixing first which is over tight iso clearances especially the rear iso.

Fix to frame is either a new frame or removing the cracked frame members and replacing with new sections plus any adjoining parts that suffer when those frame members are removed like 06.1974 and possibly 06.0414.

andover-norton.co.uk

Andover Norton Parts Drawings - Andover Norton Factory Parts - Commando Parts

Andover Norton Parts are the only Norton spare parts in the market manufactured to original drawings, within the factory-approved tolerances, from the correct materials, and with the correct finish.
andover-norton.co.uk

The other method would be to put snug fitting bracing tubes inside the cracked tubes and then welding the crack with a deep penetration weld that includes the bracing tube. The penetration weld is made easier by cutting back at the crack and exposing the inner bracing tube. A second cut will be needed up closer to the top bend and the same treatment applied with inner bracing tube. The second cut allows access to the lower crack without resorting to bending the tube and distorting it plus the Houdini antics trying to get the inner brace tube in place. By the time you have done all that you might as well bought the repair parts from AN.

The frame is plain old mild steel, no special welding equipment required other than a competent experienced welder.
 
Remove some of that nice paint , your going to have to strip a lot of parts to allow access, , you need to get a good weld all the way around , I like tig because I can , light prep , tig will penatrate , the copper coated look of tig wire is de-oxygenated wire , equivalent to weldwell 56s low hydrogen stick rods .
 
Yep ISOs adjusted too tight
On another note that nyloc ain't doing a lot?
Has it been undone to take a look?
Or was it being ridden with a spindle that's way too short?
 
In the olden days British frames were bronze welded. If you try to steel weld over bronze, you will have a problem.
If the ISOs are not tight enough you would feel it affect the handling, but if the ISOs are too tight, you will crack the frame ? - That sounds like inbuilt obsolescence.
I once looked at a Commando frame with a view to building a second race bike. I would not use one.
When the Commando was designed, Norton were paranoid about Honda CB750s being super-smooth when running, and that affected their decisions. That stupid crank balance factor was not essential. An Atlas was not a bad motorcycle.
 
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baz said:
Yep ISOs adjusted too tight
On another note that nyloc ain't doing a lot?
Has it been undone to take a look?
Or was it being ridden with a spindle that's way too short?
Click to expand...
Agreed .. the nyloc is not right . It is tight and from what i can remember , it has always been this way. This picture is the left side and you see the crack migrating into the tube and proper fitment of the nyloc
 

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Is that powder coating?


Or Bondo?


Cracked Frame


That is an impossible crack out onto the edge of a mounting tab.

Peel away the plastic & repost some pictures.
 
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Those nylocs are very deep, aren't they?

The frame members are available from A-N, and as they butt onto the spine and main loop, replacing them shouldn't put the frame out of kilter.
 
kommando said:
The cause needs fixing first which is over tight iso clearances especially the rear iso.

Fix to frame is either a new frame or removing the cracked frame members and replacing with new sections plus any adjoining parts that suffer when those frame members are removed like 06.1974 and possibly 06.0414.
Click to expand...
kommando said:
The frame is plain old mild steel, no special welding equipment required other than a competent experienced welder.
Click to expand...
Provided the frame member crack is as serious as it looks (and cracks may go beyond what's shown), replacing the frame support tubes and the rear mounting plates is the best option. Considering the frame's age and former life (wrt. fatigue and internal stresses)
I wouldn't attempt any welding work unless frame was fixed to a frame jig.

- Knut
 
Ron Hulton said:
A friend dropped over last night with his nice shiny 1971 Roadster . Shiny enough to see the frame cracked in both down tubes connecting to the rear isolastic mounting gussets . Looking for information to make proper repairs . Thanks in advance ,View attachment 108418View attachment 108418View attachment 108418
Click to expand...
May be a silly question but are you sure it's actually a crack in the tube and not just the paint/powder coat? It seems to me that a crack in the tube would not carry through to the mounting tab and it also seems that the crack wouldn't stay together in that location.
 
marshg246 said:
May be a silly question but are you sure it's actually a crack in the tube and not just the paint/powder coat? It seems to me that a crack in the tube would not carry through to the mounting tab and it also seems that the crack wouldn't stay together in that location.
Click to expand...
Never a silly question Greg .. I will have to go to his house and recheck but it sure appeared to have movement on the RH side .. If you look at the second picture i posted , the " possible " crack would appear to have started at the gusset .

Heading off shortly for a ride with a pub as our destination for lunch . Who 'da thunk ;)
 
Ron Hulton said:
Never a silly question Greg .. I will have to go to his house and recheck but it sure appeared to have movement on the RH side .. If you look at the second picture i posted , the " possible " crack would appear to have started at the gusset .

Heading off shortly for a ride with a pub as our destination for lunch . Who 'da thunk ;)
Click to expand...
We're all the welds sanded out on the frame tabs ? , for appearance, if they were weakened by this , so more flex on those tabs and continued vibration even if normal , the two isos do all the work in holding the cradle , taking the forces from the wheel and swingarm .
 
Just back from a second look ... Definitely cracked at least 3/4 the way around the tube . I was able to slide a razor blade almost through to the other side . The right side is definitely going to be the same .

Thanks for your responses ..
Cheers
 
If I was repairing that, I would make two plates to mount the ISO and extend them up the hrame tubes, so the strrsses are not concenrated at that point where the tube cracked. Manx Norton frames have the same sort of failure where the pivot mount ends
You need to get it into a frame jig, or the pivot can end up skewed.
 
Ron Hulton said:
Just back from a second look ... Definitely cracked at least 3/4 the way around the tube . I was able to slide a razor blade almost through to the other side . The right side is definitely going to be the same .

Thanks for your responses ..
Cheers
Click to expand...
Did you ask the owner what the ISOs were set at?
 
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