Classic Bike new build report

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auldblue

auldblue

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Classic Bike new build report


I recon I must have got things backward after reading Dick Finchers appraisal , no smelling of old oil and the old rose tinted view.
Classic Bike new build report

Classic Bike August 2014. New monthly feature.
 
He says 32 and 36 PSI for the tires. That seems a bit high to me. I normally run 28/ 32. Maybe I should try inflating more and see how it handles. Good article, thanks for sharing..
 
Tire pressure is something Ive always wondered about. How much depends upon the riders weight? Im in the less than 9 stone weakling category and
if I put in pressure like he says he does the bike would be bounding along like a rabbit and the center strip tire wear factor would be even more rapid
than usual.
What did Norton consider "normal" rider weight to be?
 
The bike shouldn't be that sensitive to tyre pressure - weaving due to tyres being at 29 and 33psi? I run mine at 30 and 32psi and it doesn't weave. It dosen't even weave when the rear is worn down to the wear blocks. Article states the chassis is the area which received the most attention - strange it doesn't handle then. Smoking exhaust is also not good. Are they sure it wasn't Norman Wisdom that did the rebuild?
 
I can't make out from the rather blurred pictures whether it has the original Italian 2LS front brake or not. A good hydraulic disk brake set-up would make a big differenve if it does. There's no reference to the date of the article. I'll go do some searching to see if I can find a better copy.

Thanks for the alert.
 
All Commandos are very sensitive to tires so getting good tires dialed in fr/rr air pressure can make the most pleasing difference than about anything else - [if staying in sane zone the un-tamed frame and isolastics can tolerate]. Air pressure is a sliding scale for what's best according to the surface and bike load but the best balance difference fr/rr will stay very similar, usually 2-3 lb less in front. I diddle rear PSI for best compromise of rough ride vs soft then diddle front pressure till the steering becomes the most effortless-thoughtless. Same on the sports bikes I've tested with fatso race or DOT tires. Each tire type & condition has a difference of few lbs up or down to find sweetest zone. D/T slow leaks fr or rr I've become a bit sensitive to slight warnings of ease of steering feedback that just feels like mild wind gusts or surface imperfections > till stem pulls out and rodeo handling onsets. Its educational to both over inflate tires for a while to feel how nice the iso's can isolate and steering ease like on ice skates and under inflate to get sense of alertness that next instant may hurt ya. Everyone but me and flat trackers/supermotards/off roaders, seem to think the front steers the bike and to some level of fast riding it does >but boy howdy if pressing limits and front over powers the rear's powering traction aim through turns - high side City. If find it safest besides easiest to keep rear a bit harder firmer more traction direction authority than the front. Put your hands edges inline as if tire patches and then aim them same as countersteering to see which tire you want dominate or just diddle air to find out.
 
My rule of thumb is tire pressure should rise 10% from cold to hot. Less than that, pressure's too high; more than that, pressure's too low.

I run 32F/34R.
 
Auldbike:

If you have the original Norton front brake that hasn't been modified, I would recommend at least trying the stiffening kit for the Campagnolo (I think) 2LS front brake. I did some brittle laquer distortion tests when I was at N-V and we found that, beyond about 60% brake lever movement, all the force went into distorting the backplate, rather than increasing the braking force. The stiffener kit came out about 9 months after I emigrated to the US, I think.

IMO, unless you're a date-line purist, a disk brake conversion would be well worth the money spent. Bear in mind though, that the need for a frame stiffener didn't rear its head until the front brake could generate enough bending moment to cause the fatigue failure in the top tube. I was long gone from N-V and working for Boeing by the time that problem surfaced.

I just wish Norton-Plumstead had adapted my design suggestion that was used on the production version of the AJS Stormer. That extra tube lash-up on the Commando looks really Rube Goldberg (Heath Robinson for UK readers)!
 
frankdamp said:
that the need for a frame stiffener didn't rear its head until the front brake could generate enough bending moment to cause the fatigue failure in the top tube.
Click to expand...

You keep throwing this hoary old chestnut about, Frank.
But it was a weak frame design that was the problem - if just unloading em off the truck in the crate
could damage the frame, then 'super strong' (ahem !) brakes wasn't the problem !
 
Onder said:
Tire pressure is something I've always wondered about. How much depends upon the riders weight? Im in the less than 9 stone weakling category and
If I put in pressure like he says he does the bike would be bounding along like a rabbit and the center strip tire wear factor would be even more rapid
than usual.
What did Norton consider "normal" rider weight to be?
Click to expand...

According to the Norton Workshop Manual in the Routine Maintenance Section with a single 168 lb (76.2 kg) rider it's 22 PSI Front 24 PSI Rear.
Since that is what I weigh that is what I use. I got almost 5,000 miles on my last rear tire which I suspect I wouldn't have got with the higher pressures others are using.

Two up 168 lb riders 24 Front, 28 rear.
Two up with 100 Lb luggage. 28 F 32 R

Under Technical Data in front of the manual they refer to both front and rear as being 26 PSI without mention of rider weigth or single or double riders. It does however say "Refer to Tire pressure section for permissible variation". Lack of consistency within the same manul
is disquieting.

Manual refers to 19" wheels with 4.10 tires. Dunlop Tires. (TT100 I suppose) Which is what I run.
 
rx7171 said:
According to the Norton Workshop Manual in the Routine Maintenance Section with a single 168 lb (76.2 kg) rider it's 22 PSI Front 24 PSI Rear.
Since that is what I weigh that is what I use. I got almost 5,000 miles on my last rear tire which I suspect I wouldn't have got with the higher pressures others are using.

Two up 168 lb riders 24 Front, 28 rear.
Two up with 100 Lb luggage. 28 F 32 R

Under Technical Data in front of the manual they refer to both front and rear as being 26 PSI without mention of rider weigth or single or double riders. It does however say "Refer to Tire pressure section for permissible variation". Lack of consistency within the same manul
is disquieting.

Manual refers to 19" wheels with 4.10 tires. Dunlop Tires. (TT100 I suppose) Which is what I run.
Click to expand...

That information is about 40 years old. Tyre construction has probably changed and compounds will have definitely changed. I'd go by the current manufacturers specifications. Tyre wear is also affected by the way you ride.
 
frankdamp said:
Bear in mind though, that the need for a frame stiffener didn't rear its head until the front brake could generate enough bending moment to cause the fatigue failure in the top tube. I was long gone from N-V and working for Boeing by the time that problem surfaced.
Click to expand...

Sorry Frank, but the frame breakages began to occur not long after the Commando went on sale in '68, and the modified frame had been introduced by '69, well before the Commando ever had a disc brake, and according to a Norton Service Release, the stiffening kit for the drum brake doesn't seem to have been generally available until early 1972.


http://www.automd.com/recall/campaign_c53441/
1968 Norton Commando Structure Recall 74V239000

NHTSA: Action Number: N/A Service Bulletin Number: 74V239000

Report Date:
Dec 05, 1974
Component:
Structure
Potential Units Affected:
1400
Manufacturer:
Norton/triumph Corp.

Summary:

Consequence:

Remedy:

Notes: Norton campaign no n/a. Possibility that the large diameter top tube of the main frame, may fracture in service due to unusual conditions of use following an induced weakness initiated by unsatisfactory crating and warehousing procedures. (corrective action, on machines affected, within the series of engine numbers 126125 to 128634, the frame should be changed in accordance with the instructions given in the 750cc model workshop manual (part no. 063419). )
Click to expand...
 
It's interesting that neither of the two prototypes ever showed a problem with the top tube. We really beat the crap out of those things. Once we got the various mechanical reliability issues sorted, we were doing 500 miles a day, not much of it motorways, either. Later in the program we were running 10 hours a day at the MIRA test facililty doing 100 mph on the tri-oval. With gas stops, rider swaps and chain adjustments, we got about 850 miles in the 10 hours. Those two bikes didn't have the production gas tank and seat, nor did they have side and center stands. Whether that made for different load patterns, I could say.

Whether Plumstead made changes to materials or wall thickness on the main tube after the program moved to a production development from engineering preliminary test, I don't know, but I'm surprised that just lifting the bike on and off a truck could break it.

Heavy braking "chestnut" formally retired!
 
Jerry Doe said:
He says 32 and 36 PSI for the tires. That seems a bit high to me. I normally run 28/ 32. Maybe I should try inflating more and see how it handles. Good article, thanks for sharing..
Click to expand...

Tire pressure depends more on the tire than the bike.

I forget exactly which tire, but Norman uses something like Continental or Bridgestone, which are not really common in the classic scene in the UK at least, I think CB were a bit out of order printing this pressure comment without stating which tires it refers to as others will try their advice on the 'wrong' tires!

I asked Avon directly what tire pressures should be correct for Roadriders on a Commando, and they said 32 rear and 29 front.
 
Avon recommended pressures for Roadrider 3.25x19f & 4.00x18r on my BMW R100RS are 32 & 36psi. I am running the same size tyres on the 920 Commando & using the 32/36 pressures. Did another 240 miles yesterday (one up) & believe me, it handles very well as my Goldtops will testify. Also totally stable at 110mph. I can't say how they might wear, only having done 1100 miles so far.
 
Matchless said:
Avon recommended pressures for Roadrider 3.25x19f & 4.00x18r on my BMW R100RS are 32 & 36psi. I am running the same size tyres on the 920 Commando & using the 32/36 pressures.
Click to expand...

I know tyre pressures can be a matter of personal preference and often subject to change to suit different riding conditions, but the Avon recommendation is 29F/32R for a Commando fitted with Roadriders.


Front Tyre
Roadrider
Pressure front:
2.0 bar (29psi)
Front size:
4.10-19 61H TT or 100/90-19 57V
Rear Tyre
Roadrider
Pressure rear:
2.2 bar (32psi)
Rear size:
4.10-19 61H TT or 100/90-19 57V
Click to expand...

(According to the Avon website, the recommended pressures for a BMW R100RS [1977-85] 3.25-19/4.00-18 Roadriders is 32F/40R)
 
I asked Avon directly what tire pressures should be correct for Roadriders on a Commando, and they said 32 rear and 29 front.
Click to expand...



interesting!

like you I also called Avon and asked what tire pressure for their RoadRiders

they told me 32 front and 35 rear, single normal weight rider

they said modern tires are manufactured under much better quality control than long ago
and therefore can, and should, withstand higher psi than in the past
 
frankdamp said:
It's interesting that neither of the two prototypes ever showed a problem with the top tube. We really beat the crap out of those things. Once we got the various mechanical reliability issues sorted, we were doing 500 miles a day, not much of it motorways, either. Later in the program we were running 10 hours a day at the MIRA test facililty doing 100 mph on the tri-oval. With gas stops, rider swaps and chain adjustments, we got about 850 miles in the 10 hours. Those two bikes didn't have the production gas tank and seat, nor did they have side and center stands. Whether that made for different load patterns, I could say.

Whether Plumstead made changes to materials or wall thickness on the main tube after the program moved to a production development from engineering preliminary test, I don't know, but I'm surprised that just lifting the bike on and off a truck could break it.
Click to expand...
There's a piece about it in this month's copy of the NOC's Roadholder magazine.
Subsequent testing to induce frame breakage was apparently carried out at the MoD testing ground in Cobham, Surrey. Two of the factory testers involved were Alan Jones and Bill Hawkins (do you remember them, Frank?).
Apparently, according to the article: "The bikes did 3,000 jumps, and were also ridden along railway sleepers to see if they could break the frames. The frames would break the down tubes, and a lot of the testers ended up in hospital...." :shock:
 
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