Introduction and 1968 Frame Question

Joined
Jan 13, 2006
Messages
2
Hi all!

I'm a proud new owner of a 1968 Commando Fastback. The bike is in good running and aesthetic condition as it is now, is all original (except color) and has less than 8000 original miles. It will be fun to rebuild.

I found this group during one of my "12 hour" googling sessions. Seems like a great group!

Now my question - the bike is an early 1968 model with the 'weak' frame - ie no serial number and no support tube (one way to look at it, I guess, is that I have a fairly rare bike, so to speak, and one of the earlier Commandos made in the 'fastback' style). However - I would like to ride the thing a little before emarking on a complete teardown and rebuild, if possible.

Is the frame really that dangerous? Books/manuals seem to just glance over this issue, but then there are a few email posts I've seen where people say don't even get on the bike with that frame.

Any thoughts? If I do go with an updated frame, how much will going with a non-original frame affect the value? If I ever decide to show the bike, will that greatly affect my potential 'ranking'? I'm new to this, so feel free to be blunt!!!

Thanks!!!! :D
 
Joined
Apr 7, 2004
Messages
1,691
Most of the stories of these going away have been of it happening slowly durring a ride. It just starts handling very strange and upon checking the it out the frame is found cracked. It's a rare bike that I wouldn't press hard in the twisties. Just something to keep your eyes on. norbsa
 

jimbo

VIP MEMBER
Joined
Sep 25, 2004
Messages
1,756
Country flag
Is there any damage on your frame? Look it over under the tank. I have 1968 Norton factory letters and theories on the subject.The experts do not agree.
 
Joined
Jan 13, 2006
Messages
2
jimbo said:
Is there any damage on your frame? Look it over under the tank. I have 1968 Norton factory letters and theories on the subject.The experts do not agree.


The frame is in great shape. No sign of trouble around the steering head/backbone/downtubes...
 
Joined
Oct 7, 2005
Messages
1,170
Not having kept in touch with the Commando after I left Norton in June of 1968, I wasn't aware of any frame problems. When I did the structural stiffness testing, I think we came up with vertical stiffness about 3 times better than the Featherbed and torsional stiffness about 8 times better.

We did find a problem, on the AJS motocross bike, where the wrap-around stiffener between the top tube and the headstock was welded to the top tube. That step change in stiffness caused a stress increase which resulted in fatigue cracks in the top tube. At the time, I didn't see a problem for the Commando because the stiffener was below the top tube, rather than above it like the AJS frame, and it wasn't subject to the kind of punishment that the AJS suffered.

The only drawback to frames as stiff as the Commando is that the suspension has to do a much better job with small motions. On "softer" structures, these motions are often absorbed in deflections of the minor frame members.

The motocross environment was particularly harsh. Often, you would burn your hand if you touched the rear suspension dampers after a race. It was common to have discoloration of the paint on the dampers.

Interestingly, even with a frame top tube completely separated, the bike was still rideable. The fuel tank seemed to keep it all together!

My opinion is that frame failure on the Commando would be low probability (unless there was significant corrosion) and it's more a long-term fatigue issue, unlikely to be a catastrophic collapse.

Has there been any history of catastrphic failure in service? If there has been, were the bikes ridden off road a lot? I can't see normal paved road irregularities causing a fatigue failure for a 100,000 miles or more. If you ride through Manhattan at 120 mph on a regular basis, that may be detrimental (but to more than the frame!)

This topic is news to me.
 

jimbo

VIP MEMBER
Joined
Sep 25, 2004
Messages
1,756
Country flag
Brian Slark was around then too, I think he has said the frames broke because they were weak, and needed the support of the extra tubes( like the newer frames).As I said ,the experts do not agree!
 
Joined
Apr 7, 2004
Messages
1,691
Well I am not spewing often repeated lines of talk. I am saying what I have seen all 68 style frames riden hard regularly will break deal with it. Show me one un broken and I will show you one never used hard. If you ride one no big deal watch the frame real close ride it till it brakes. Unless your doing 80 mph it probly woun't kill ya. norbsa
 

jimbo

VIP MEMBER
Joined
Sep 25, 2004
Messages
1,756
Country flag
norbsa48503 said:
Well I am not spewing often repeated lines of talk. I am saying what I have seen all 68 style frames riden hard regularly will break deal with it. Show me one un broken and I will show you one never used hard. If you ride one no big deal watch the frame real close ride it till it brakes. Unless your doing 80 mph it probly woun't kill ya. norbsa

I have a tendency to agree. I ride mine very politely,trying not to break an antique .
 
Joined
Oct 7, 2005
Messages
1,170
Interesting! Where do they break?

On the AJS M-X frame, we replaced the top tube and stiffener with a tapered top member made from two sections. At the headstock, the assembly consisted of two welded sections that were semicircular at the top/bottom with parallel sides. The overall height was tha same as the length of the headstock. The corss-section then tapered down until, at the joint with the seat support, it was circular. Essentially, we took the top tube, split it along its horizontal centerline and inserted a triangular web, though the actual stucture was two pressings and had just a single centerline weld. If anyone's interested, I can do a drawing.

I believe the AJS design was sold off to Bombardier, as I've seen a few motocross bikes from them with what looked a lot like the AJS frame and the N-V proprietary way of adjusting chain tesion by means of an eccentric swing-arm pivot.
 

L.A.B.

Moderator
VIP MEMBER
Joined
Nov 20, 2004
Messages
17,750
Country flag
jat312 said:
Is the frame really that dangerous? Books/manuals seem to just glance over this issue,

'Norton Commando' written by Mick Duckworth mentions the frame breakage problem in some detail and is worth reading as it is an excellent book.
 
Joined
Jan 15, 2006
Messages
54
'68 frame

My suggestion would be to look for a replacement frame and put this original one in the rafters for the future. Unless it's strickly for show. If you do use it, do not put a disc brake front end on. The stresses generated by a good disc setup can flex the forks. Imagine this added force working on that frame. Not good.
The impression I got from the district rep for Berliner (the importer) was that the frames had been replaced by them. I have no details about when, how, or who. The subject came up when I showed him a parts bike I had purchased, a '68 fastback with the same frame. This is the only one I ever saw.
Unfortunately, I still needed a frame! Driving into the side of a left turning Chevy Impala at 50mph had destroyed mine. The steering head had ripped open the frame just behind the weld. I had to cut the frame apart to remove the engine. The rep found me a frame that someone had braced. They had welded a solid plate into the space between the main tube and the smaller under tube. This filled the entire area, no gaps. Overkill. However, they had the right idea. Years later, it was discovered in Superbike racing that when you applied force to the front end, that the upper frame tubes would spread apart. Not conducive to good handling, so they started welding short tubes between them. (hmm, might be why that was the best handling Norton I ever rode) :)
 
Joined
Oct 7, 2005
Messages
1,170
I guess that, during the time I was at Norton, the problem never showed up, as all my riding was done before the disk brake appeared in production. We tried a couple of disk installations, but they didn't work because the basic design was for a sliding disk instead of a sliding caliper.

Top brass had spent so much money on an image make-over (the famous "Green Hemisphere" badge) that there wasn't enough left for engineering development work.
 
Top