Rear Frame Breakage

Status
Not open for further replies.
Woody850

Woody850

Joined
Sep 30, 2017
Messages
325
Country flag
This summer I plan on doing a bit of two up riding and have heard the rear loop of the frame can break.
My seat has all the rubber buffers in place and sits on the mudguard while the mounts are in good condition.
The weight of my passanger should be around 60 kg's no more and no luggage will be taken other than maybe a tank rucksack.
Is this an unfounded rumour?
 
Perhaps you mean the rear loop can bend behind the shock mounts (The inner plate extended rearward by the factory to try and minimise that)
 
What vintage Norton? I did a lot of pillion and camping gear riding on my MKII and the frame loop is fine.
 
If you were rebuilding a bike from the bare frame with the short inner and outer plates (750 ?) then it might be worth considering adding an extended inner if loads were planned.
On a bike together might be something else.
If you have an 850 its factory done already.
 
The issue is if you attach saddle bags to the loop and add too much weight. If you look at the design of the Andover luggage rack the support strut goes down to the passenger footpeg so the weight is not suspended off the loop.

andover-norton.co.uk

Motorcycle parts and spares for Norton motorbikes - Genuine Andover Norton Spare Parts - Andover Norton Motorcycles Parts - Original Andover Norton Parts

Motorcycle parts and spares for Andover Norton motorbikes: Andover Norton manufactures and supplies all Genuine Factory Spare Parts for Norton motorcycles built before 2002.
andover-norton.co.uk
 
Last edited:
johnm said:
The issue is if you attach saddle bags to the loop and add too much weight. If you look at the design of the Andover luggage rack the support strut goes down to the passenger footpeg so the weight is not suspended off the loop.
Click to expand...
No problem, saddlebags are an eyesore for me. I toured once with a river rafting roll on the rear seat, comfy and watertight.
 
Since I usually do mine from scratch I cut the frame at the shock mount area, put a piece of solid inside about 4" long and plug weld on either side of the cut area and then weld the cut area. I usually run bags so it is safe from bending now.For regular light loads I wouldn't bother.
 
maylar said:
What vintage Norton? I did a lot of pillion and camping gear riding on my MKII and the frame loop is fine.
Click to expand...
The chassis should never be subjected to heavy loads in that area, it's simply not designed for it.
Even panniers with their own carrier made by Craven supply load bearing arms to spread the load.
Look up the Craven website.
 
All rear weights on the loop should be moved forwards. I have a passenger support rail installed that puts that seat weight well forwards , to the shocks area. A curved plate to match the fender curve. The passenger/ luggage will land weight on this area , not the rear portion of the rail. Think about it and cut some steel.
 
Woody850 said:
This summer I plan on doing a bit of two up riding and have heard the rear loop of the frame can break.
My seat has all the rubber buffers in place and sits on the mudguard while the mounts are in good condition.
The weight of my passanger should be around 60 kg's no more and no luggage will be taken other than maybe a tank rucksack.
Is this an unfounded rumour?
Click to expand...
Check "Commando Service Notes" from the Norton Owners Club (reproduced on this website). On page 26, at the bottom, it discusses frame breakage at the junction of the battery tray weld if too much weight is carried on a parcel rack without a reinforcing strut going to the footrest hanger. Also discusses same location frame breakage if rear Isolastic is not properly adjusted, i.e., too tight. When I bought my 1974 Commando in 1975, with less than 2K miles on it, the frame had been replaced according to the seller, by the dealer due to the latter problem (Isolastics too tight). I bought the bike anyway after a careful exam showed no other damage and everything "shipshape". I was disbelieving, somewhat, until years later I bought the Norton Service Notes and there it was. Selling the bike now, 3062 miles (Austin TX Craigslist). Kept in my house for all intervening years. At 84 and 134#, I cannot kick it over! (I hate being old.) I put so few miles on the '74 as I had a '73 I bought a few months old in ''74 and rode that one exclusively for many years. I have had many bikes, 86, but always kept the Norton as it was my delightful link to an earlier time in my life.

Ralph
 
Woody850 said:
Mine is a 73 850 Roadster.
Thank you both, then I am relieved :)
Click to expand...
73 850's did not have the reinforcement at the upper shock mount area. At least not my early 73 850 does. I'm not sure when that was added, but I have a 74 frame that does have it. You will be able to look at yours and see the extra plate on the inside of the shock mount to rear loop tubing.
 
Deckard said:
73 850's did not have the reinforcement at the upper shock mount area. At least not my early 73 850 does. I'm not sure when that was added, but I have a 74 frame that does have it. You will be able to look at yours and see the extra plate on the inside of the shock mount to rear loop tubing.
Click to expand...

If your frame has that already, you're good.
Since you're just worried about a passenger, 60kg (132 lbs) is not something I'd worry about unless the road surface could cause suspension bottoming, etc. Then you'd have far more issues than this.....
 
Generally the Interstate is much more susceptible to the rear frame droop problem than the roadster, because the pillion sits much further back and therefore puts more bending moment on the unsupported section of the frame loop. A roadster with a 60kg passenger should be no problem.
 
myjota said:
Generally the Interstate is much more susceptible to the rear frame droop problem than the roadster, because the pillion sits much further back and therefore puts more bending moment on the unsupported section of the frame loop. A roadster with a 60kg passenger should be no problem.
Click to expand...
My bike came to me as Hirider (please hold your snickering pls!) and it had rear hoop droop, despite having almost no room for pillion on that hideous banana seat.
 
Bend the loop back. Reverse the pressures that caused it in the first place. Then weld in 2 side support plates so it does not happen again. If you travel like we do then all your camping gear heavy weight should be placed as forward as possible and the lighter sleeping bags should only be to the rear. Lightest to the rear. Many rack choices out there.
 
Torontonian said:
Bend the loop back. Reverse the pressures that caused it in the first place. Then weld in 2 side support plates so it does not happen again. If you travel like we do then all your camping gear heavy weight should be placed as forward as possible and the lighter sleeping bags should only be to the rear. Lightest to the rear. Many rack choices out there.
Click to expand...
The side support plates will be insufficient once a certain load criteria on the back is reached, it will be even worse if you hit a load of bumps or hit a couple of "sleeping policemen " at speed.
I refer to my earlier post regarding support arms to the footrests re Craven carrier.
 
  • Like
Reactions: baz
Rider sit on first, pillion get on second, the seat is effectively a see saw, many onwers have done many miles two up like this and not had an issue.
 
Status
Not open for further replies.

Similar threads

T
  • Locked
rear frame loop strength
2
Replies
30
Views
3,127
bwolfie
B
Back
Top