New Owner of '68 Commando

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If you've seen pics of the widowmaker Commando frames after they've cracked,
they break just under the weld on the short reinforcement to the steering head.
Could be nasty if you were motoring at the time.

I'd guess (not having seen one up close in the metal) that the weld has thinned and weakened the top tube in that area,
rather than reinforced and dissipated the stresses.

BTW, the old lugged Norton frames are somewhat prone to cracking through some of the lugs.
And featherbeds had problems with their steering heads bending, until they were braced with additional gussets.
Getting the bugs out of new designs kept many a maker busy back in the good old days...

Oddly, Matchless frames had fewer problems - figure that one out ?
Although were not totally immune.
It has been suggested they were not as heavy, and a little flex allowed them to survive better ?
 
So I'll ask the question again since we're talking widowmaker frames. Is it worth more to leave it in its original shape or does modifying it matter? Of course I know repairing it makes it safer, but original condition seems to be rarer nowadays. If I do go the route of non-repair I'd have it magnafluxed to look for any cracks or anomolies. However I'm open to suggestions.
 
My opinion is (and that's all it is) if you want to ride it, fix it or get a new frame, or if you want to put it in a museum, leave it. I doubt if leaving it will increase it's value much except to a museum or collector.

Dave
 
Yes, if you are planning to ride it, the problem is that the frame breakage occurs up under the tank.
Where it is near invisible to spot, until your front end folds under you ?
Crack testing it today is no guarantee it will be safe to ride next year, or next week even ?

Something that original makes it near a museum piece only ?
Doubt that makes it more valuable to most collectors ??
 
Rohan said:
Oddly, Matchless frames had fewer problems - figure that one out ?
Although were not totally immune.
It has been suggested they were not as heavy, and a little flex allowed them to survive better ?
Click to expand...

I wouldn't say they were not as heavy. The N15/G15 Frame has got to be about 45 lbs. including the rear subframe and swing arm
New Owner of '68 Commando


The P11 is a much lighter frame, but still has that heavy Matchless head stock where the frame tubes are pressed in and brazed
New Owner of '68 Commando


I think the key to the Matchless frame strength is the heavy headstock and pressed-in and brazed frame tubes
 
BillT said:
I think the key to the Matchless frame strength is the heavy headstock and pressed-in and brazed frame tubes
Click to expand...

Earlier Norton frames used lugs and tubes brazed in - with quite heavy grades of tubing used.
Some of those (pre featherbed type) frames cracked, a lot.

I have an earlier Matchless lugged frame (1949), with quite light looking lugs and tubing.
Much lighter all around than the same year Nortons.
I've never seen or heard of those Matchless frames cracking, so something is going on here.
Vibration analysis can sometimes show that tubes that crack may be vibrating in certain harmonics to cause them to crack,
so the reasons may not be so simple to determine.... ?
Road shocks that feed stresses into certain spots in the frame, rather than dissipate them may also be involved.

Which could certainly be the case for the Commando widowmaker frames.
Wasn't there some discussion that unloading them off the transporter jarred the headstock, very heavily ??
 
Rohan said:
jimbo said:
My bike has the original frame and it is not broke ( I keep an eye on it :shock: )
Click to expand...

Be very careful with that train of thought, and policy.
You may not get a whole lot of warning when it lets go - and spears you head first into the tarmac.
Click to expand...


This is how keep on top of my frame.
I have a baseline measurement between the axles noted on a string with knots.I measure the distance before and after every time I ride . As the frame starts to give way the distance will become greater. I also fiercely tug on the front wheel to feel any abnormal movements. There was a bulletin mentioning these things many tears ago. :mrgreen:
 
What happens if it all lets go suddenly ??!

I know of someone who broke the headstock of their old (lugged frame) ES2 completely off when they were going through a creek.
Fortunately quite slowly.
The whole fork and front wheel just went its own way.

They thought it was hilarious - but then no-one got hurt.....
 
I'm kidding everybody! I just putz around on the ole girl,people were passing me left and right at Barbers :oops:
 
Putting about gently at docile shown' tell Rallys is all very well and good. I recall one O.N.O. rally near Welland where we all did some aggressive twisties up down and around where my Crazy hit farm machinery gravel and the rear end kicked out sideways before a wobbly recovery. You never know where life may lead you on a Widdowmaker frame ? Weld in a bracetube. :|
 
The failure is caused by the gusset from the top tube to the steering head-stock being a significant discontinuity in bending stiffness. This causes a localized increase in stress due to bending (I'd guess maybe 5x). The problem didn't show up in prototype testing because we had the original 2LS Italian brakes, which would be hard pressed to stop a 125 Bantam.

Once people started putting more powerful front brakes on the bikes, particularly after-market mods, the problem showed up.

It's interesting to me that the AJS moto-cross team bikes showed the exact same failure, although upside down. The frame's head-stock/top-tube was the same as the Commando, except the connection was at the bottom of the head-stock, producing the stress raiser on the upper half of the top tube. We had several total failures of the top tube in competition, with the fuel tank attachments being the only things holding the frame together.

Being an aero/mechanical engineer, I understood stress raisers well and suggested a fix which became the AJS Stormer production frame. I think it was a lot more elegant than the extra tube in the Commando. The top tube was redesigned as a 4-piece assembly, with two semicircular cross section pieces (that were the two halves of the original) split length-wise from the head-stock to the seat cross-member, along the horizontal center-line. These were set up so that the cross section at the aft end was circular. At the head-stock end , the two C-shaped pieces were spaced out to meet the head-stock tube very close to its top and bottom edges. The triangular space from the head-stock to the seat cross-member on each side was filled with a long triangle of sheet steel, welded along its edges to the two C-sections.

The re-design didn't appear in production until a few months after I left N-V, but I understand that the works M-X bikes didn't have any more failures. It's a pity, IMO, that Plumstead weren't made aware of the common failure mode of the two frames and of the fix intrduced in the Stormer.
 
Frank,

I really enjoy hearing your real life factory experience. Thanks for sharing this.

Dennis
 
frankdamp said:
Once people started putting more powerful front brakes on the bikes, particularly after-market mods, the problem showed up.
Click to expand...


The problem shows up in completely stock bikes ??

In fact, it showed up very early in the bikes life.
Wasn't there some discussion initially that it was caused by rough unloading from the transport,
when delivering new bikes to Dealers.
Then more of them started breaking....
 
Rohan said:
frankdamp said:
Once people started putting more powerful front brakes on the bikes, particularly after-market mods, the problem showed up.
Click to expand...


The problem shows up in completely stock bikes ??

In fact, it showed up very early in the bikes life.
Wasn't there some discussion initially that it was caused by rough unloading from the transport,
when delivering new bikes to Dealers.
Then more of them started breaking....
Click to expand...

The frame breakages certainly began fairly early on, well before any "powerful brakes" were available for the Commando.

New Owner of '68 Commando

"Ken Sprayson:

.....The main ingredient of of Bauer's design was a 'backbone' top tube, 2¼ inches in diameter by 16swg (.064 ins), the bottom loops forming the rest of the mainframe being only 1 inch in diameter. The welded joint of the 2¼ inch top tube to the steering head was braced with an all enveloping gusset resulting in a relatively 'solid' section. In addition to this, both the steering stops and the petrol tank mountings were welded onto the 1 inch down-tubes. From previous experience, I felt that both of these features were possible points of failure.
How right I was. From the first 100 frames shipped to America, a considerable number of breakages were reported. When told of these failures, Reynolds metallurgical department immediately instigated a test programme to investigate any possible faults in the welding procedure. The report concluded that there was no fault in either the welds or the tube, but failure had occurred due to impact loading. Frames were collapsing immediately behind the top tube/steering head gusset as well as failing in the area of the welded-on attachments to the front down tubes. Another broken 'spine' on a bike that had done about 1500 miles, was subjected to a further test which concluded that the initial damage was due to impact loads propagated by vibrations in service. It turned out that motorcycles shipped to America were individually crated and offloaded by crane onto waiting lorries [trucks]. When the lorries arrived at their destination there was no lifting gear available, so crates were literally pushed off the back of the truck from a height of anything up to six feet. Further tests were done at Reynolds simulating this situation which proved the point that collapsing was occurring even before the bikes were un-crated. ....."
Click to expand...
 
Rohan said:
........
Wasn't there some discussion initially that it was caused by rough unloading from the transport,
when delivering new bikes to Dealers.
Then more of them started breaking....
Click to expand...
Yes Frame breakage was blamed on poor transport, I have documents suggesting the bikes were held down by the tank mounts which was the real problem(or one of them) , the bracket was welded across the down tubes( bad practice really) and when the bikes were cinched down to that bracket the welds cracked. With the down tubes compromised the main tube couldn't cope.
 
When I started working for NV in September 69 I was given the guided tour. The drawing office was in the small upstairs part of a 25,000 sq. ft factory that /NV were renting. Downstairs was the factory floor. There was some of the "stuff" that had been emptied out of Plumstead, AMC drawing stores, some jigs and fixtures, hack motorbikes and about 50 or 60 dismantled Commandos, It was explained that they had a frame that was liable to catastrophic failure and had been recalled. All the parts other than the frames were being reabsorbed into production wherever possible. The frames all went for scrap. One of the draftsmen (not me) tried to buy a frame to build a racer around. He was refused as the frame break, when it happened, was completely out of the blue, with no warning at all, and the rider was sliding down the road on his or her face, if they were lucky. If they weren't lucky they were dead.
cheers
wakeup
 
That white zip tie is precisely where they break.
Starting from underneath first.

Maybe its covering something ?!!?
 
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