Norton Low Boy

Below is a scan from a Clymer Norton manual (Third printing - February 1980) showing dimensions for the 750 Commando frame. The manual includes a near identical illustration for the 850 Commando frame. From what I have seen the only difference is that the steering head angle went from 27 degrees on the 750 frames to 28 degrees on the 850 frames. Everything else (primary dimensions) appears the same. I do recall some discussions about difference in shock mounts, rear frame loops and some ancillary bracketry but the primary dimensions appear to remain identical between the 750 and 850.



Would be interesting if we could get a compare and contrast between the Norvil (lowered) frame dimensions and the illustration above.

Just for the record, the original Norton Lowboy frame was for a Manx Norton - lowered a good few inches and used a heavy lower fork yoke (no upper fork yoke, at all !).
Classic Bike or someone showed a restored one a few years ago.
Dommie lowboy frame came later, didn't do the odd yoke bit....

murraycod0; if you would oblige to take a few measurements it would be appreciated. I think the two telling dimensions will be from the centerline of the frame loop to the top ISO mount (shown as 9.45") and from the iso loop to the centerline of the bottom tubes of the frame (shown as 10.80")

You nail these two down for your frame and I think it will paint the picture.

Relax getting attention from the likes of John Maygar is a feather in my cap - even if annoying as hell most the time. Only just now learned only special after market lowering available for isolastic Cdo's. Acotrel my jaw went slack and groin tightened watching that hydrid powering around like crazy. It take special bike and places to commit life to that wreck-less handling.

Kenny low boy racer, not a Commando of course. scroll to find.
http://nycnorton.com/bikes/

Colorado Norton Works lowers Cdo's w/o altering frame, but would have to ping Matt to learn how they did it.
http://www.coloradonortonworks.com/about/cafe.asp
Because the frame geometry was left untouched and the bike was lowered it handles exceptionally well like most Commandos. The Lowering will compromise ground clearance but the lower center of gravity is very noticeable and exciting in corners. Koni shocks and a 38mm Marzocchi fork ensure that suspension is on par with engine performance.

hobot said:

Relax getting attention from the likes of John Maygar is a feather in my cap

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That's interesting - along the lines of "Thank you sir, may I have another" :lol: Judging by your response I doubt you are relaxed - but that's irrelevant.
Thought you were heading to Barber?

hobot said:

Colorado Norton Works lowers Cdo's w/o altering frame, but would have to ping Matt to learn how they did it.

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How about 18" wheels

and

stuffing the forks further up into the triple clamps

and

maybe lower profile tires.

Exactly. Shorter springs and fork tubes up front, and shorter shocks in the back plus 18"s.?

The cradle is aluminium from RGM but where the cotter pins go in it is very week around the welds so thinking about beefing that up somehow The oil tank is stainless as the sidecover as well which are part of the package along with shorter shocks that you need.I am thinking about a corbin seat.I will check some frame measurements as best I can In a week or so when I am back from holiday cheers

Thanks murraycod0. At your leisure.

Seen the Swing Arm pin ' Clamps ' , Steve has the link . Effective fix . Means the pin will come out if necessary without a large hydraulic whatsit if fitted interferance .

Norton fing on up Newcastleish next the 11th , know the form ? .

I'm as relaxed as after getting laid as getting more riding in than a lot of yoose guys this season and fall colors here are starting to pop best in a decade. Mostly lolly gagging in tree covered secondary roads but did wipe the newness off sides of rear tire on well named Race Track Road I used to freak out on when unpaved Gravel but now as good as Barbers with better scenery and no traffic. Decided too much time away to do Barbers this year especially with serious antagonist to dodge. I lost another day to prep homestead for winter - wasting it with Wesley. We stopped after RTR to look back after climb out of Kings river valley to view an expansive vista - both of us exclaiming what a surreal wonder land then headed out to Eureka Springs biker Victorian town - even a gal walked up to ask what year mine was, then straightened up surprised, saying her girl friend nailed it! The barkeep that does counter top dances and bare breast to breast bumps with other gals says coming to see me to keep up the pace : ) Stopped at Beaver Lake Dam taking in the breeze when a bus load of Amish paraded down the hiway to look over edge of dam. Wes and I slowly rode past them in their Sunday dress uniforms, I yelled out "Looking Good" and got grins and waves from even their leader. Come out out after Barbers, last week of October is peak colors blaze. I've not touched a drop of the good stuff just hoping to see ya flat on ya face so relaxed couldn't care less who ya's seen with...

Best not to lower the whole frame as seriously hinders corner clearance. Chopping the top down like Norvil seems best route then the other areas mentioned plus seat padding cut down. Or could go the hard tail chopper route with extended front forks to get the lean clearance back and only lose handiness in parking lot maneuvers but fine on the fly. Can't cut down shocks too much w/o adding more spring or tire may hit fender on bumps. 18" rim don't lower hardly any but 17" front and 16 rear sure could.

There are special metals to put on touch points that make lots of extra sparks over just plain mild steel. The only place Peel gets any Titanium is at tips of crash cage since training wheels limit lean angle. First Norton ride I ever did was so lean limited I finished a steep down hill vertical wheelie on the LH frame rail both tires locked in sideways snow skiier stop...
http://www.gadgetjq.com/sparks.htm
titanium, when it contacts pavement and scrapes across it creates a shower of very bright white sparks which can be pretty impressive to a rider behind you, especially the first time you touch one down on a night ride.

I was interested that the 850 frame uses 28 degree head angle, and the 750 uses 27 degrees. Apparently all Seeleys use 27 degrees. To keep the same geometry when changing wheel size by one inch dia. the frame head angle usually changes by half of one degree. I suggest it is important to recognise whether your steering is neutral, oversteering, or understeering. If you ride the bike over several laps on a race circuit, it becomes obvious where it finishes up coming out of corners under power when you are relaxed. If it steers towards the centre of the track in the direction that it is laid over, that is good (oversteering ). You can get on the gas really early, and go faster down the straights. I don't believe the height of the bike is very important as long as nothing grounds when it is laid right over.

Hobot, the old guy with the Norton twin engined featherbed racer was not all silly. The bike would be stable and fast, even if the handling was not brilliant. It would be a good thing to ride. I got a real buzz out of watching that video. It reminded me of better(?) days. I spent 12 years racing my short stroke 500cc featherbed Triumph. My mate had a similar 650, and we went at it hammer and tongs over very many enjoyable race meetings. I never managed to beat him convincingly, and he will never bring his 650 Triumph anywhere near my Seeley commando 850, so he has escaped unscathed. These days he is concentrating on riding on the salt at Lake Gairdner in South Australia where it is more difficult to lose skin.

Dances with Shrapnel said:

From the Clymer manual the 750 Commandos had a 27 degree head angle and the 850's had a 28 degree head angle. Would be interesting to hear if the offset on the 750 triple clamps was different than that for the 850.

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John, my recollection is that the 850 yokes pulled the wheel back by using unequal offsets in the top and bottom yokes, with the holes bored at a slight angle, not by reducing the offset and keeping the forks parallel to the stem, as they are in the 750. They kept the same wheelbase, while increasing the trail slightly, supposedly to cure the dreaded Commando head shake. I don't recall where I read that, and I could be mistaken, but the memory of it is pretty strong. The funhy thing is that I never experienced any head shake in racing the 750, but did encounter it regularly with a MK3 on the street.

Ken

Ken, that's my recollection about the 850 triple clamps but memory is too distant for me. I ran a Mk3 sleeved to 750 in AHRMA for a few years and it was steady as a rock. Never a hint of head shake but then I was using 18" rims, wider rims than stock and wider profile race tires.

Only odd behaviour about it was a really high speed weave coming off the bank into the back straight at Daytona. Reproduceable but stable; never got awayfrom me.

My Mk2a for the street takes constant vigilance (hands on the bars) or else it will go into a full blown tank slapper.

Decipering the info , the 850 has 1/2 in more trail , effectively . SO is near same axle to steering head
disposition as First 68 / 69 triple clamps ( the Ancient H/Lamp Ear type ) .

I would have thought that head shake is more likely to come from the isolastics and suspension, rather than geometry. You need to have the intention to recognise whether the bike is understeering, oversteering, or neutral. Unless you are looking for the characteristics, you will ride around your handling difficulties. With my own bike, I always ride it for a few laps before using its oversteer with a heap of power. It oversteers a lot as the weight comes off the front end, and you have to anticipate where it will end up on the bitumen,when coming out of corners. You might expect it to hang itself up on the outside guard rail, but if it is oversteering it will end up track centre, when you apply no pressure. When this stuff happens, you might think you are imagining it and it feels strange to gas the bike hard long before you can see up the next straightaway.
On three corners our local circuit there is a drop off the outside edge of the bitumen of about 2 inches. If you run off a bit and try to get back on too quickly, it is possible for the edge to steer the bike out from under you. We sometimes see riders fall off in a straight line and roll along in the grass. Running wide in corners is bad news. With my old Triumph, I was always fighting to keep it on the bitumen in corners, my Seeley does none of that exhausting garbage. (In that little photo to the right , you can see that I am climbing off the bike to get it around, while the other guys are sitting up doing it easy.) Like all of this road racing stuff, it pays to 'go fast slowly' !

Yeah Man - Now ya talking acetrel! The Rear Rules The Roost! Best not depend on the dang front tire really powering through turns eh. Alas not for too low slung bikes of course.

Dances with Shrapnel said:

Ken, that's my recollection about the 850 triple clamps but memory is too distant for me. I ran a Mk3 sleeved to 750 in AHRMA for a few years and it was steady as a rock. Never a hint of head shake but then I was using 18" rims, wider rims than stock and wider profile race tires.

Only odd behaviour about it was a really high speed weave coming off the bank into the back straight at Daytona. Reproduceable but stable; never got awayfrom me.

My Mk2a for the street takes constant vigilance (hands on the bars) or else it will go into a full blown tank slapper.

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That sounds about like my experience. I started racing my PR in 1972 with the original 19" K81s, 3.60 front and 4.10 rear. I later switched to the Dunlop triangulars, still 19". By the time I got to my first Daytona race in 1985, I was up to 18" Michelin slicks on wider mag wheels. In a lot of years of racing that bike, I never experienced any sort of weave, tank slapper, or any "hinge in the middle" feelings. I did raise the rear a bit, drop the front a bit, and use adjustable triples (Spondon) to find the right amount of trail. All I ever did to the original isos (including the top mount) was adjust them. The only times I had handling problems was when the rear axle broke (twice), when the swingarm broke, and when the front slider broke at the axle hole. All my other crashes were pretty much rider error, not bike problems. That's why I was always surprised by stories of head shake and wobbles and such in Commandos, at least until I had the MK3 that exhibited a scary sort of front end wobble at slow speeds, especially when going down hill. I never did figure out the cause. It also had 18" tires. My current street Norton is another MK3, this time with 19" wheels, and it seems to handle fine, even with the bent frame (that I plan to eventually fix).

Ken

Had to get a new nut machined for the maney outrigger so it reached the cradle slot adjuster.Twin adjusters for the belt drive.

lcrken said:

Dances with Shrapnel said:

From the Clymer manual the 750 Commandos had a 27 degree head angle and the 850's had a 28 degree head angle. Would be interesting to hear if the offset on the 750 triple clamps was different than that for the 850.

Click to expand...

John, my recollection is that the 850 yokes pulled the wheel back by using unequal offsets in the top and bottom yokes, with the holes bored at a slight angle, not by reducing the offset and keeping the forks parallel to the stem, as they are in the 750. They kept the same wheelbase, while increasing the trail slightly, supposedly to cure the dreaded Commando head shake. I don't recall where I read that, and I could be mistaken, but the memory of it is pretty strong. The funhy thing is that I never experienced any head shake in racing the 750, but did encounter it regularly with a MK3 on the street.

Ken

Click to expand...

I put 850 trees on my "71 frame. It dramatically quickened the steering. It is a little easier to get the dreaded head shake, but if you just ride through it it never becomes a problem. Lose is fast right?? I thought it was a great improvement over the stock trees. I haven't been able to afford the alloy rims yet but the decreased trail aleviated the angular resistance noticably. I can steer much more with my body than before.

-Strong

Thanks for the "eye candy" shot of your cradle and swingarm murraycod0. Cj