Discussion in 'Norton Commando Motorcycles (Classic)' started by jseng1, Mar 17, 2018.
You could also do similar to pre MK3 if you also add a chain tensioner and fix the gearbox position.
Having to have main shaft land in fixed position to match up with fixed support bearing imply about impossible with chain but completely practical with belt drive - once proper loose tension set, nail gb down/marked, as proper tension of cold belt can be worked on/off pulleys and needs cold 'slack' to tolerate ride heat tightening up or may risk bending main shaft when it does. I think BY FAR its an over tight chain or belt that bends shaft, way more than pure power plays do, unless at world class race power which famously lost races d/t drive train failures.
Thinking on how I'd do it - would lay cycle horizontal, align/tension everything then JBW in case bearing and later create rear cradle/case back up support insurance. If ever needed to replace case bearing, just heat to 600'F-ish to soften JBW then slice or or slowly press out.
Every Unit Brit engine has fixed shaft positions and some even do without tensions at the expense of slack chains.
You are right at pointing out the tolerance issue of the engine/cradle and g/b shell/cradle fixings. I believe the major issue here is that the g/b fixing needs to be tied to the primary case and ultimately to the c/shaft centre datum point. Thus, a new g/b case and a different kind of cradle is required. Admittedly, this gets complicated. I think CNW's latest development - the e-start - shows that a semi-unit engine layout in which the inner primary cover becomes a load-bearing member is the natural evolution of design. Interesting intellectual exercise anyway. Whether it is "worth it" is no valid statement to an engineer! :-D
my only fear in the cnw starters is the torque moment that is put on the 3 1/4 bolts and central stud of the inner case. norton did increase the mounting hardware size and quantity on the mk3 BUT so far it does not seem to be an issue wit the cnw unit
What's your point, 84ok? That there is a TTi box available which makes an outrigger bearing redundant? Well, it's not available for the Mk3, unless Bruce Verdon desides to make a left shift variant. I doubt that's going to happen, although the required modification seems to be small, as assessed by these pictures.
On another note, I read somewhere that Comnoz has started modifying his TTi box - if he intends fitting that g/b to his Mk3 road bike, maybe we will see some development in that direction?
Oh but they did! But that chaincase needs to be rigidly mounted, more so than the standard location set screws.
The works Norton solution was to weld an inner chaincase to the crank cases with a bearing mounted in a fixed location for the gearbox shaft. I looked at it in the late '70s, I got sent some sketches and notes by one of the Redferns, but I didn't have any access to the required machine shop! Don't have the info today either.
Actually the fixed shaft centre distances should work better with a belt drive.
But your other solution today is a TTi gearbox, which may seem expensive, but if you have to buy in machine shop time is probably cheaper all round.
thanks for this interesting information. I tried to search for images of the monocoque and space frame F1 engines but couldn't find any showing the inner primary case. If someone has complementary images, please post.
Why does fixed shaft centres work better with a belt drive, if no idler pulley is fitted? Maybe it can be skipped in racing engines because the belt is replaced within a few hours of operation, but surely not for a powerplant used on the open road where the belt is expected to last at least 500 hours?
Agreed, the TTi gearbox is an alternative, although I am uneasy as to how much better the mainshaft support really is. Although the countershaft looks rugged enough, the mainshaft still looks spindly to me.
A belt should not need adjusting, so if it’s set correctly with fixed centres it should work perfectly, without requiring any form of tensioner.
A chain wears, so if running fixed centres, would need some kind of tensioner.
Hence, fixed centre mod on a Cdo would be ‘better’ with a belt.
I can assure you that the TTI boxes are near bullet proof and provide the reliable shifting. If you go to their site there is a side by side comparison of a few of the critical components.
If you run a TTI, there’s no need for an outrigger bearing.
These pictures are from a Peter Williams presentation in New Zealand in 2007. I don't have a link to the web site I downloaded them from, but it's probably still out there somewhere.
Very nice and informative. They look rugged enough. Thank you for posting, Ken. I see no sign of the inner chaincase being welded to the crankcase though?
For those interested in the idea of an outboard bearing tied to the engine cases, this is a picture of the way Jim Schmidt (jseng1) did it on his monoshock Norton back in the '80s. It was two pieces, with the front plate was welded to the crankcase, and the rear plate bolted to it. Worked quite well.
All the ones I've seen were bolted, not welded, but you never know what the factory might have tried back then. This is a picture of the primary case that I took some years ago of an original factory race bike that was owned by the Frutiger brothers. It's now part of Jamie Waters' collection.
And yet another one with the primary case bolted on. This is a Phil Aynsley picture of the bike that Peter Williams rode to victory in the 1973 IOM Formula 750 race.
Should work or will work???
At the risk of being arrested for going off-topic, I am inclined to question your statement. Any engineered material subjected to considerable tensile forces will elongate. There is also the effect of creep in steel as well as polymer materials. Accoring to Gates, the pre-tension during installation is between 1.9 and 2.03% and by repeating this several times as per Gates' instructions, I can only guess that the initial pre-tension is aout 2.5-3%. Further elongation is expected during its lifetime.
How do you achieve the required pre-tension and later re-tensioning with fixed centres and no jockey?
I looked up some old postings by Comnoz and lernt that he re-fitted an adjuster to his (Mk3) g/box in order to run a primary belt drive. On unit-engines the advise by those in-the-know is to retain the slipper tensioner (less rubber layer). This will require some lubrication though.
By neglecting belt tensioning, you will encounter a transmission loss of up to 10% according to an engieering source I looked up. Of course you are also at risk distroying the belt.
outrigger bearings are new to me, i assumed that it was mostly a hi-po option here, the stock box being suitable for usual street use
In a non unit Norton is not the belt fitted rather loose, and that it tightens up as the engine gets hot?
Mine sure did. Is this the result of the power unit being non unit?
Well Knut, I am only speaking from personal experience, I’ve never researched the theory on this.
Bob Newby supplies kits for unit Triumphs, no tensioner, extremely high reputation for reliability.
Tony Hayward is a tad more vague, saying that ‘some do and some dont’! But I have never run a tensioner with Hayward belts, inc my 906cc NRE with unit cases, and a pre unit Nourish engine that I made engine plates for with fixed centres.
P&M belt kit for triples has no tensioner.
My current Cdo has a belt, I fitted double adjusters as you’re supposed to, but I’ve never adjusted them since fitting.
I suspect that the stretch quoted by your research is smaller than the margin of error any of us amateurs have when setting belt tension anyway, so I suspect it’s all rather acedemic to be honest.
As I said, I never looked up the theory though! Maybe I was (and am) losing power? I honestly don’t know, but it worked (and continues work) for me.
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