No reason why it wouldn't work, but how do you fix the centres accurately to ensure that the bearing runs correctly, it would need reamed holes to locate the gearbox and engine onto the cradle, the engineering in doing it is not impossible but involved so just does make it worth it.
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.
-Knut
Hi guys,
I am wondering why no one has come up with a beefed-up Mk3 inner primary chaincase featuring an integrated mainshaft bearing similar to the one provided by Maney? Sure, this would be limited to chain drive primary only. Having watched close up pictures of the g/b mounting and the final drive sprocket, see e.g., the Commando workshop manual companion, it seems there is ample space for a cotton reel steel spacer between upper g/b bolt and inner primary case. For the lower bolt, a direct attachment isn't possible because the frame rail obstructs. However, a stiff exchange member either in steel or aluminum is easily fabricated as there is ample space between bolt and final drive sprocket. For a trial test of the design, the chaincase facing the final drive sprocket could be skimmed around the mainshaft boss and a strenthening plate be fitted by bolts or nails. Function of the OEM seal could be maintained by a sealed bearing.
Is there an obvious reason why such a design wouldn't work? OK, additional shimming may be required to overcome casting tolerances and to avoid bending stresses in the inner chaincase, but that's a one-time operation. Any thoughts?
-Knut
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.
-Knut
SteveA,
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.
-Knut
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.
<snip>
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?
-Knut
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.
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.
https://www.accessnorton.com/NortonCommando/inside-the-tti-gearbox.4983/
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?
-Knut
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.
-Knut