Does a 1973 750 commando frame have a different geometry than a 1974 850?

As I understand it the later 1° de raked yokes should not be used on the early 27° frame
But the earlier parallel yokes can be used on either frame
Also I may be wrong but I believe the CNW yokes are bored parallel and are used on either type frame
​
 
mdt-son said:
Not sure what Greg actually replied to here. Parts fit, but that doesn't mean they are interchangeable.
It's advisable to use 750 triple trees for 750 frames, and 850 triple trees for 850 frames. Your spares list for the year in question should be your prime guidance.

- Knut
Click to expand...
The 850 triple trees add 1 degree. The frames are the same. The 1 degree was to improve handling. Putting 850 on 750 is an improvement. Putting 750 on a 850 means that the handling will be 750, not 850. IMHO, putting 850 triple trees on a 750 is a good thing so when I have a bad 750 triple tree, I use an 850 triple tree when I can't find a replacement 750.
 
marshg246 said:
The 850 triple trees add 1 degree. The frames are the same. The 1 degree was to improve handling. Putting 850 on 750 is an improvement. Putting 750 on a 850 means that the handling will be 750, not 850. IMHO, putting 850 triple trees on a 750 is a good thing so when I have a bad 750 triple tree, I use an 850 triple tree when I can't find a replacement 750.
Click to expand...
The link that LAB posted says that the frames are NOT the same. Scroll down to section F and there's separate drawings for 850 and 750 frames with different headstock angles listed....


Honestly, I have an early model bike so I don't keep up with the later model specs, and I thought the later 750 and 850 frames were the same too, but the link seems to show they are not.... unless I'm somehow misinterpreting the diagram in section F. Check it out, I'd actually like to know the answer...
 
NickZ said:
Am I correct in inferring that the changes to the 850 frame and 850 triple trees were made simply as a handling improvement, but not necessitated by having the 850 engine?
Click to expand...
Yes, nothing is related to the engine, the frame does not care which engine is fitted.
 
baz said:
As I understand it the later 1° de raked yokes should not be used on the early 27° frame
But the earlier parallel yokes can be used on either frame
Also I may be wrong but I believe the CNW yokes are bored parallel and are used on either type frame
​
Click to expand...
Correct.
All aftermarket yokes like cNw, RGM, etc are bored parallel.
 
baz said:
As I understand it the later 1° de raked yokes should not be used on the early 27° frame
Click to expand...


If a pair of yokes are ordered from AN for a 750 frame, they will supply 850 yokes (when in stock).
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
"(USE 06.4080 + 06.4078) (AS A PAIR)"
 
What huge can of "my head hurts" worms

So in a nut shell, a person could use nonMK3 ANG 850 yokes together on a 73 750 frame without a problem
 
marshg246 said:
The 850 triple trees add 1 degree. The frames are the same.
Click to expand...
??
The 850 tripple tree 'adds' absolutely nothing.
ALL it does is putting the contact point of the front wheel further back, and thus increase trail.
The angle of the fork legs itself has little or no effect on how a bike handles.
Well demonstrated by Tony Foale:
motochassis.com

Experiments with steering geometry » Motochassis by Tony Foale

© Tony Foale. 2000-2018. (The experiments were conducted around 1982/83.) Rake The author’s ideas mentioned in other articles in relation to the angle of the steering axis (rake) were subsequently put to the test by modifying a readily available standard production machine – a BMW R75/5. There...
motochassis.com motochassis.com
 
Last edited:
marshg246 said:
The 850 triple trees add 1 degree. The frames are the same. The 1 degree was to improve handling. Putting 850 on 750 is an improvement. Putting 750 on a 850 means that the handling will be 750, not 850. IMHO, putting 850 triple trees on a 750 is a good thing so when I have a bad 750 triple tree, I use an 850 triple tree when I can't find a replacement 750.
Click to expand...
Greg, considering your vast knowledge in all things Norton Commando, I am surprised you have missed the sketch in the workshop manual which clearly states the 850 and 750 frames are NOT identical.

"The 850 triple trees add 1 degree". Add to what? It's a 1 degree reduction vs. the 750 yokes. The frame rake remains at 28 degrees (62 degrees measured against ground horizontal) for an 850 frame. The net effect is a substantial increase in trail of 850 frame and 850 yokes vs. 750 frame and 750 yokes.

Fitting 750 yokes to an 850 frame reduces trail vs. the stock 850 combination, but trail will still be larger than on the 750 frame/750 yokes combination. You claim handling is similar to a stock 750. I can't verify this. Others may chime in.
Fitting 850 yokes to a 750 frame increases trail vs. the stock 750 combination, but trail will be lesser than on an 850 frame/850 yokes combination. You say this combo improves handling (against the stock combination). How so?

The factory made extensive road tests using professional test riders to determine the best combination in demanding loadcases. I doubt any of us is experienced enough to recommend the factory's design to be overridden. This throws up the question, does AN really vouch for fitting 850 yokes to genuine 750 frames? Hitherto I have considered their offering to be valid for their 1971-on replacement frames only which are all made to 850 specification.
Apart from opinions of what works and what doesn't, there is also the question of eligibility. The bike received type approval using a certain combination of parts. By fitting non-standard parts, the bike is no longer type approved. Loss of e.g., direction stability caused by fitting non-standard parts could have severe health and financial implications. Hence, jimbo, we have to be careful with statements like fitting non-standard yokes "without a problem". If anyone opts to do it, it is on his/her own risk.

- Knut
 
Last edited:
jimbo said:
What huge can of "my head hurts" worms

So in a nut shell, a person could use nonMK3 ANG 850 yokes together on a 73 750 frame without a problem
Click to expand...
Maybe/Probably.
Year on thee machines aren't definitive.
Need to match up serial numbers.
The Mk V 750 has the 850 accoutrements, square tailight, black clock holders et.
The Mk V, #220*** is considered the 73.

The Norvil Motorcycle Company supply spares, accessories and parts for Norton and Norvil bikes

Norvil Motorcycle Co Ltd manufacture & sell Norton spares for pre 1977 Nortons
www.norvilmotorcycle.co.uk
What's the first three digit's of the ser. #?

There is an inmate here who has from new, a Mk V who could verify this issue.
Ron L. He'll probably be along sometime.
 
mdt-son said:
Greg, considering your vast knowledge in all things Norton Commando, I am surprised you have missed the sketch in the workshop manual which clearly states the 850 and 750 frames are NOT identical.

"The 850 triple trees add 1 degree". Add to what? It's a 1 degree reduction vs. the 750 yokes. The frame rake remains at 28 degrees (62 degrees measured against ground horizontal) for an 850 frame. The net effect is a substantial increase in trail of 850 frame and 850 yokes vs. 750 frame and 750 yokes.

Fitting 750 yokes to an 850 frame reduces trail vs. the stock 850 combination, but trail will still be larger than on the 750 frame/750 yokes combination. You claim handling is similar to a stock 750. I can't verify this. Others may chime in.
Fitting 850 yokes to a 750 frame increases trail vs. the stock 750 combination, but trail will be lesser than on an 850 frame/850 yokes combination. You say this combo improves handling (against the stock combination). How so?

The factory made extensive road tests using professional test riders to determine the best combination in demanding loadcases. I doubt any of us is experienced enough to recommend the factory's design to be overridden. This throws up the question, does AN really vouch for fitting 850 yokes to genuine 750 frames? Hitherto I have considered their offering to be valid for their 1971-on replacement frames only which are all made to 850 specification.
Apart from opinions of what works and what doesn't, there is also the question of eligility. The bike received type approval using a certain combination of parts. By fitting non-standard parts, the bike is no longer type approved. Loss of e.g., direction stability caused by fitting non-standard parts could have severe health and financial implications. Hence, jimbo, we have to be careful with statements like fitting non-standard yokes "without a problem". If anyone opts to do it, it is on his/her own risk.

- Knut
Click to expand...
I have put 850 yokes on a 750 without problem and riding around town and on the Interstate, I can feel no difference.

The 750 and 850 top yokes are the same. The 750 and 850 bottom yokes differ by one degree.

According to my workshop manuals, both the 750 and 850 frames have the headstock at 62 degrees from the ground. There are some differences at the rear of the frame, but none I can see that have anything to do with the yokes.

As @L.A.B. said, when you order a set from AN, you get ANG top and bottom, in other words 850.

As far as "type approved", that has no meaning 50 years later, at least in the US. It would be really rare to find a 100% stock Commando on the street in the US and it would be impossible to find an inspector who would have a clue!

AFAIAK, the Norton engineers decided that the 1 degree of difference was better for handling.

Like all comments/advice here, there is always at least one naysayer and everyone should consider the validity of the info.

Sounds like you are against installing brakes that actually work, tires that hold the road better, superior ignition systems, etc.
 
MichaelB said:
Maybe/Probably.
Year on thee machines aren't definitive.
Need to match up serial numbers.
The Mk V 750 has the 850 accoutrements, square tailight, black clock holders et.
The Mk V, #220*** is considered the 73.

The Norvil Motorcycle Company supply spares, accessories and parts for Norton and Norvil bikes

Norvil Motorcycle Co Ltd manufacture & sell Norton spares for pre 1977 Nortons
www.norvilmotorcycle.co.uk
What's the first three digit's of the ser. #?

There is an inmate here who has from new, a Mk V who could verify this issue.
Ron L. He'll probably be along sometime.
Click to expand...
See if the underside of your current yokes is marked "ANG". If your serial number starts with 230 or 235 if may well be "850" frame.
 
I'm still not hearing the answer to the question I asked...

IS there a different headstock angle for late model 750's and 850's??

And the 1 degree yokes don't improve the "handling", they slow the handling and improve "stability" by lengthening the amount of trail...... as Ludwig already pointed out...

LAB, I consider you the encyclopedia of Commando.. What do you say? Do the late 750's and 850's have different headstock angles as was shown in the link you posted?
 
The change was made to correct steering head waggle. The '71-'72 frames had a habit of waggling at speeds of around 35MPH or so. It didn't really affect handling that much but there were customer complaints. Not every bike did it but some did. My '72 had this habit. It was found that by changing the rake 1 degree and altering the yokes by 1 degree corrected the problem.
 
marshg246 said:
The 750 and 850 top yokes are the same.
Click to expand...

They can't be the same due to the angularity of the fork legs. According to dynodave the top yoke dimensions are not the same.
Post in thread 'Fork yokes - simple question'
dynodave

Post in thread 'Fork yokes - simple question'

o0norton0o said:
Here we go again.... The yoke offset was changed (made about 1/2" greater) AND the yoke angle was increased from 27 degrees to 28 degrees. The result was a minor increase in trail of the later model so it added a little bit of stability to the later model and made it a tiny bit heavier steering with a slightly slower response....
Click to expand...

OP:
What were the yoke offsets for the first and second models of Commandos ?

These are the 3 configurations
1. series 1 commando rolling chassis (68-69-70) used 27 deg (as I said in post #3) 2-1/4" offsert same as featherbed/all late slimline but...

Oct 14, 2020

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o0norton0o said:
Here we go again.... The yoke offset was changed (made about 1/2" greater) AND the yoke angle was increased from 27 degrees to 28 degrees. The result was a minor increase in trail of the later model so it added a little bit of stability to the later model and made it a tiny bit heavier steering with a slightly slower response....


OP:
What were the yoke offsets for the first and second models of Commandos ?

These are the 3 configurations
1. series 1 commando rolling chassis (68-69-70) used 27 deg (as I said in post #3) 2-1/4" offsert same as featherbed/all late slimline but all UN threads on commando triple trees

2. series 2A commando/ 71,72,73 750 rolling chassis still 27 degree but increased new fork offset and style top2.777" bottom 2.783"

3. series 2B commando / 850 rolling chassis NOW 28 degree and 850/ANG top 2.851" bottom 2.689"


marshg246 said:
According to my workshop manuals, both the 750 and 850 frames have the headstock at 62 degrees from the ground.
Click to expand...

Most, if not all, manuals don't say that. If the frames were the same, then there wouldn't be a drawing of each. The 750 frame drawing in Service Release N. 78, March 72, also shows 63 degrees.

750 = 63.
Does a 1973 750 commando frame have a different geometry than a 1974 850?

850 = 62.
Does a 1973 750 commando frame have a different geometry than a 1974 850?
 
Last edited:
marshg246 said:
As L.A.B. said, when you order a set from AN, you get ANG top and bottom, in other words 850.
Click to expand...
Greg, I question the validity of that statement. I'd prefer to hear AN's official statement on this issue. AN is generally very restrictive deviating from stock. Did NV ever issue a TN approving retrofit of 850 yokes to 750 frames?
If it is beneficial to handling, I for one would expect such a recommendation.

marshg246 said:
As far as "type approved", that has no meaning 50 years later, at least in the US. It would be really rare to find a 100% stock Commando on the street in the US and it would be impossible to find an inspector who would have a clue!
Click to expand...
While I don't know US legislation on road safety etc., I would expect DMV and NHTSA to handle this seriously. Fitting non-standard parts affecting road safety is an issue that needs to be taken seriously, no matter how old the vehicle is.
What owners might do and whether inspectors have a clue or not is a different matter irrelevant to this discussion.
Also, I don't see selection of tires, brakes and electrical components being relevant to this discussion.

marshg246 said:
AFAIAK, the Norton engineers decided that the 1 degree of difference was better for handling.
Click to expand...
Well, it's more like 2 degrees effectively wrt. to the trail.

marshg246 said:
Sounds like you are against installing brakes that actually work, tires that hold the road better, superior ignition systems, etc.
Click to expand...
I guess you wrote this in a moment of emotional arousal? I may change this and that on my bikes, but I will be reluctant to make general recommendations, especially on safety-related components.

- Knut
 
NickZ said:
Am I correct in inferring that the changes to the 850 frame and 850 triple trees were made simply as a handling improvement, but not necessitated by having the 850 engine?
Click to expand...
NicZ, there is probably an indirect relationship between engine size (torque), weight and weight distribution, speed, and handling. The Commando models put on weight as years went by, which does affect handling. When comparing an early Fastback and the Mk3 for instance, there is a significant difference in most respects. Legislation and test criterions may have changed too, prompting an increase in required margins of safety. Thus, we can't view "handling" as an isolated parameter.

- Knut
 
MichaelB said:
Maybe/Probably.
Year on thee machines aren't definitive.
Need to match up serial numbers.
The Mk V 750 has the 850 accoutrements, square tailight, black clock holders et.
The Mk V, #220*** is considered the 73.

The Norvil Motorcycle Company supply spares, accessories and parts for Norton and Norvil bikes

Norvil Motorcycle Co Ltd manufacture & sell Norton spares for pre 1977 Nortons
www.norvilmotorcycle.co.uk
What's the first three digit's of the ser. #? 1973 750 212082

There is an inmate here who has from new, a Mk V who could verify this issue.
Ron L. He'll probably be along sometime.
Click to expand...


1973 750 212082
 


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