Mk3 changes from 74 models
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The Parts Books.
Great for insomniacs...
When you looks at all the areas that changed, its easy to believe that number.
With electric start, crossover gear shaft, auto primary chain tensioner, rear disc brake,
instrument binnacle and top mounted ign key, folding seat, blah blah blah.
Lotta bits to do all that...
Great for insomniacs...
When you looks at all the areas that changed, its easy to believe that number.
With electric start, crossover gear shaft, auto primary chain tensioner, rear disc brake,
instrument binnacle and top mounted ign key, folding seat, blah blah blah.
Lotta bits to do all that...
I don't think I could pick up all of the changes from the parts book, though someone more observant might. Even so, how does one get details of the actual change from a parts book?
For example, was thickness added to the crankcases in critical areas, as compared to earlier 850s? I know the crank was strengthened with larger bolts, were there any other changes? There were also frame and swingarm changes, the ISO change and so on.
The parts book doesn't detail the type of change or give dimensions, just a new part number which doesn't really tell you much, other than that there has been a change of some sort made.
Glen
For example, was thickness added to the crankcases in critical areas, as compared to earlier 850s? I know the crank was strengthened with larger bolts, were there any other changes? There were also frame and swingarm changes, the ISO change and so on.
The parts book doesn't detail the type of change or give dimensions, just a new part number which doesn't really tell you much, other than that there has been a change of some sort made.
Glen
If you want those sort of precise details, read the brochures,
in conjunction with the parts books and workshop manuals.
Or even just compare the 2 bikes, side by side. Eyes laddie, eyes.
Unless you are writing a magazine article for publication, who would need to know this sort of detail. ??
Just ride and enjoy...
in conjunction with the parts books and workshop manuals.
Or even just compare the 2 bikes, side by side. Eyes laddie, eyes.
Unless you are writing a magazine article for publication, who would need to know this sort of detail. ??
Just ride and enjoy...
Having the two models to compare (I don't) would be helpful for external differences. Then there are all of the internal differences. Neither the manuals nor the brochures list the all of the changes and for the most part give very little detail.
I am simply curious about the changes and I imagine some other MK3 owners or prospective owners are as well.
If there is no publication listing these changes, then perhaps owners could post the changes they are aware of here. At some point I will compile it into a list and make it available to anyone interested.
I'll start with some of the obvious stuff:
Electric Start
120 watt rm 21 changed to 180 watt rm 23 alternator
Shimmable isos changed to Vernier Isos
Sealed and strengthened swing arm (how is it strengthened?)
Right hand shift changed to left hand
Rear drum brake changed to disc
Front disc switched to left side
I am simply curious about the changes and I imagine some other MK3 owners or prospective owners are as well.
If there is no publication listing these changes, then perhaps owners could post the changes they are aware of here. At some point I will compile it into a list and make it available to anyone interested.
I'll start with some of the obvious stuff:
Electric Start
120 watt rm 21 changed to 180 watt rm 23 alternator
Shimmable isos changed to Vernier Isos
Sealed and strengthened swing arm (how is it strengthened?)
Right hand shift changed to left hand
Rear drum brake changed to disc
Front disc switched to left side
A
Anonymous
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Rear chain adjusters pull instead of push. M3?
Ta.
Ta.
Was the rear wheel quick detachable on the earlier model? Obviously it is a much changed part due to the brake change, just wondering if the earlier type was as easy for wheel removal. With the mk 3 the chain and sprocket stay put and the wheel with rotor falls away at the cush setup.
Glen
Glen
Ron L
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1) front hub bearing retainer
2) lapseam fuel tank (Roadster)
3) handlebar switches
4) ignition switch console
5) upper triple tree
6) headlight shell
7) wiring harness connectors
8) left sidecover
9) airbox
10) battery tray
11) seat (hinged and different upholstery)
12) front fender lacks front stay
13) rear hub
14) crankcases
15) crankshaft
16) timing cover
17) footpeg mounts
18) primary covers
19) engine cradle
20) inner and outer gearbox covers
21) frame loop reinforcement tabs (for seat lock)
Those are just off the top of my head.
2) lapseam fuel tank (Roadster)
3) handlebar switches
4) ignition switch console
5) upper triple tree
6) headlight shell
7) wiring harness connectors
8) left sidecover
9) airbox
10) battery tray
11) seat (hinged and different upholstery)
12) front fender lacks front stay
13) rear hub
14) crankcases
15) crankshaft
16) timing cover
17) footpeg mounts
18) primary covers
19) engine cradle
20) inner and outer gearbox covers
21) frame loop reinforcement tabs (for seat lock)
Those are just off the top of my head.
Check valve on pressure side of pump.
Then there is the other oil plumbing change Jim Comstock described today. I haven't gotten my head around that, need to reread the thread.
One change that was a retrograde step was going back to the rh4 head from the rh 10 of 1974.
Then there is the other oil plumbing change Jim Comstock described today. I haven't gotten my head around that, need to reread the thread.
One change that was a retrograde step was going back to the rh4 head from the rh 10 of 1974.
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.
Not much left to pick over here, as Ron L. grabbed all the low-hanging fruit.
Exhaust headers are designed differently, at the end that inserts into the head, with a conical design sitting on a mating conically shaped ring, allowing for adjustment on more than one axis.
Two zener diodes on the MK III, one in each of the two Z plates, so the left side Z plates on the MK III have an extra hole to accomodate the 2nd zener diode.
Transmission has an electric neutral indicator, but there is no longer any type of indicator for which gear you're in, unless you're in neutral.
Gear shift lever changed from chromed steel on earlier bikes, to aluminum on the MK III.
Read somewhere the oil pump itself is somehow different, to be compatible witht he different MK III timing cover. May just be the button seal that faces the timing cover.
Timing cover differences, generally referred to in Ron L's post, are the inspection cover for the cam chain, and an anti-sump valve, and maybe others? I think Jim Comstock provided information that there is more than one design of MK III timing cover.
Also read/learned from another thread here that MK III's have rims specific to the model. Might have been L.A.B. that posted that.
Front brake master cylinder, and brake line set up, which passes through the lower triple tree.
Ron L specifically mentions upper triple tree, but the lower triple tree is different, too, and has an extra hole to accomodate brake line.
There are slight differences between center-stands on '74 and '75 models, although I haven't paid enough attention over the years to cite them specifically.
I believe the location of the rectifier may have moved, too. Or I have a bike where someone has mounted it in a different location than stock.
Depending on which models are being compared, the chainguards would have differences. Some 1974 chainguards have a cut-away to allow access to the brake inspection hole.
Regarding seat specifics, I've noticed that on at least 1974 MK II models, the foam is a different shape, and has a little extra meat at the rear end that rises up. Not sure if I've ever seen a '73 model with this, so I think it might be unique to 1974 models.
MK III fork locks have a rubber plug to prevent water from entering the lock. It's attached at the triple tree stem.
The facings of the Smith tach and speedometer are different on the MK III. The Veglia gauges I'm not sure about, but I think the '74 Veglia guages may have had some iteration of the green globe, whereas the MK III models I've seen, with Veglia guages, have the blue and white arrows. Same with the Smith guages.
The MK III added a trip odometer, too.
Are the speedometer drives different? They mount on opposite sides.
What about the rear axles? I don't know for sure.
The mufflers will be different, if comparing '74 models equipped with pea-shooters.
Almost forgot the kick start lever, which is bent differently than on all previous models, and allows for greater clearance from the exhaust system.
Oil tanks are different, too, as the chain oiler was removed on MK III. Not sure if all MK III were like this, if '74 MK IIA bikes had a chain oiler.
The left sidecover has already been mentioned, but for people following the thread there are two different '74 Roadster and Interstate sidecovers, with and without space for the toolkit, and the different lower mounting point that features an extra hole in the sidecover at the lower mounting point, for the MK IIA models.
Isolastics were already mentioned, but not the head steady with the additional spring and hardware to mount it.
The stickers on the frame were different, too, I believe. And I've got a MK III with original paint and there's no reserve sticker for the petcocks, where there is on my '74.
On my MK III there is no fuel baffling in the gas tank, but there is in my MK II tank.
There are different shapes of muffler mounts (the plates attaching to the Z plates), but I'm not familiar enough to describe them. Not even sure what's correct on the different models.
.
Not much left to pick over here, as Ron L. grabbed all the low-hanging fruit.
Exhaust headers are designed differently, at the end that inserts into the head, with a conical design sitting on a mating conically shaped ring, allowing for adjustment on more than one axis.
Two zener diodes on the MK III, one in each of the two Z plates, so the left side Z plates on the MK III have an extra hole to accomodate the 2nd zener diode.
Transmission has an electric neutral indicator, but there is no longer any type of indicator for which gear you're in, unless you're in neutral.
Gear shift lever changed from chromed steel on earlier bikes, to aluminum on the MK III.
Read somewhere the oil pump itself is somehow different, to be compatible witht he different MK III timing cover. May just be the button seal that faces the timing cover.
Timing cover differences, generally referred to in Ron L's post, are the inspection cover for the cam chain, and an anti-sump valve, and maybe others? I think Jim Comstock provided information that there is more than one design of MK III timing cover.
Also read/learned from another thread here that MK III's have rims specific to the model. Might have been L.A.B. that posted that.
Front brake master cylinder, and brake line set up, which passes through the lower triple tree.
Ron L specifically mentions upper triple tree, but the lower triple tree is different, too, and has an extra hole to accomodate brake line.
There are slight differences between center-stands on '74 and '75 models, although I haven't paid enough attention over the years to cite them specifically.
I believe the location of the rectifier may have moved, too. Or I have a bike where someone has mounted it in a different location than stock.
Depending on which models are being compared, the chainguards would have differences. Some 1974 chainguards have a cut-away to allow access to the brake inspection hole.
Regarding seat specifics, I've noticed that on at least 1974 MK II models, the foam is a different shape, and has a little extra meat at the rear end that rises up. Not sure if I've ever seen a '73 model with this, so I think it might be unique to 1974 models.
MK III fork locks have a rubber plug to prevent water from entering the lock. It's attached at the triple tree stem.
The facings of the Smith tach and speedometer are different on the MK III. The Veglia gauges I'm not sure about, but I think the '74 Veglia guages may have had some iteration of the green globe, whereas the MK III models I've seen, with Veglia guages, have the blue and white arrows. Same with the Smith guages.
The MK III added a trip odometer, too.
Are the speedometer drives different? They mount on opposite sides.
What about the rear axles? I don't know for sure.
The mufflers will be different, if comparing '74 models equipped with pea-shooters.
Almost forgot the kick start lever, which is bent differently than on all previous models, and allows for greater clearance from the exhaust system.
Oil tanks are different, too, as the chain oiler was removed on MK III. Not sure if all MK III were like this, if '74 MK IIA bikes had a chain oiler.
The left sidecover has already been mentioned, but for people following the thread there are two different '74 Roadster and Interstate sidecovers, with and without space for the toolkit, and the different lower mounting point that features an extra hole in the sidecover at the lower mounting point, for the MK IIA models.
Isolastics were already mentioned, but not the head steady with the additional spring and hardware to mount it.
The stickers on the frame were different, too, I believe. And I've got a MK III with original paint and there's no reserve sticker for the petcocks, where there is on my '74.
On my MK III there is no fuel baffling in the gas tank, but there is in my MK II tank.
There are different shapes of muffler mounts (the plates attaching to the Z plates), but I'm not familiar enough to describe them. Not even sure what's correct on the different models.
.
trident sam
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There are differences between mk 3 bikes aswell, some bikes have a cranckase protrusion on the drive side case front , below the iso mounting also the brake pedals were altered from a more rounded solid type to a straighter hollow type. Hey, they never stood still at that factory :shock:
sam
sam
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Deets55 said:
The higher 2nd gear set was first used the 850 Mk.1A in late 1973, and the Mk.2/2A models.
Danno said:
No? :? If you just read it, then it's probably the OPRV oil blow-off vent you are thinking of?
worntorn said:
There were so many differences-it would probably be easier to list the parts that didn't change-rather than list those that did. :wink:
lcrken
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Crankcase and crankshaft related changes:worntorn said:
The crankcase is thicker in some areas, in particular at the upper rear area where the earlier cases are pretty thin, and tend to crack.
The crankshaft is wider than earlier models, and the main bearing bores in the cases are further apart to accommodate it.
As you mentioned, the crankshaft fasteners were increased from 5/16" to 3/8" diameter.
The main seal in the crankcase is held in place by a wire circlip, as opposed to the earlier cases where the seal is pressed in against a lip in the crankcase.
The output shaft of the crankshaft is longer to accommodate the sprag clutch for the starter.
The alternator is mounted further out, on a separate mounting plate, which sites on four mounting studs from the crankcase, as opposed to three on earlier models.
On the timing side, in addition to changes in the oil distribution and return system, there is a difference in the width of the pinion gear, and maybe also the intermediate gear, but I've forgotten the exact details. I do recall that it is possible to narrow the earlier gears to fit by grinding or turning on a lathe.
The MK3 also had the addition of a plug in the timing side crankcase half, with a corresponding slot milled in the crankshaft cheek, that allowed locking the crank at TDC by removing the plug and inserting a tool that fits into the milled slot.
The timing cover has had a plug added that can be removed to check the cam chain play.
That's it off the top of my head for crankcase and shaft changes.
Ken
Thanks for the crankcase and crankshaft info Ken.
I have heard the Commando described as an old fashioned cobbled together bike with an ancient engine, however it is clear that the designers at Norton were not afraid of change and redesign. I like to think that for the most part they kept the good bits but strengthened weak areas and generally refined things as much as possible with the MK3.
I suppose it is safe to say that if one was to build a moderately hotrodded Commando and wanted to use stock cases and crank to limit the cost, a MK3 850 would be a good starting point.
Glen
I have heard the Commando described as an old fashioned cobbled together bike with an ancient engine, however it is clear that the designers at Norton were not afraid of change and redesign. I like to think that for the most part they kept the good bits but strengthened weak areas and generally refined things as much as possible with the MK3.
I suppose it is safe to say that if one was to build a moderately hotrodded Commando and wanted to use stock cases and crank to limit the cost, a MK3 850 would be a good starting point.
Glen
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