1973 850 Mono shock / showa forks.

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bwolfie

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Today I stripped dorn the $300, 1993 GSXR 750 donor bike, 2 hours and a bare frame/motor is all that is left. Got home and tossed the parts at my frame. This is going to be awesome when I finish it. Pictures here.
Everything looks close/easy to adapt. a few shafts, bearings, some milling and a little welding.

http://s1029.photobucket.com/albums/y35 ... ld%202010/

1973 850 Mono shock / showa forks.
 
Is the front wheel off the GSXR? Looks like a Norton rear hub and sprocket. What size rims are you running?

lookin good so far.
 
Looks like fun, but you still have a certain limitation on tire width due to the narrow spacing between the frame centerline and the drive sprocket centerline.

Still, you can get in a 120/90 which is pretty nice...
 
Looks real interesting, the front end appears to be the easy part, but I reckon the back end is going to take fair bit more effort. Do you intend to fit the alloy swing arm to the original gearbox cradle swing arm mount?

Mick
 
Bowolfe, that is something to take notice of. Enjoy just putting my mind in your mental space of fantasy coming true with head and bottom scratching hang ups.
Less unsprung mass at rear and moves shock mass more forward central, cool.

You might consider a rear link that ties both sides of frame together to both sides of cradle to take on the side loads that swing arm just invites. Far away from rear iso the better but any where back there should about solve hinged handling, which mostly comes from rear patch levering side/side on front mount into forks and back. Also a front link, maybe under slung through mount like Jim Comstock instead of above mount like my down dirty test version. If I ever saw that combo in our village or at a track day I'd quake in my seat to picture contesting with it.

Maybe if you can space out rear sprocket, chain would clear 130 tire. Which sure would be sexy but don't know it too big to bother with.
 
The wheels are from my Norton. I'm going to lade up a dual disk hub in the front. The gsxr disks are a 5 bolt pattern, but about 1/8" larger circle diameter. so i'll index it and drill/tap new holes. I'm not going any bigger with the tires, They were stuffed into the stock parts, so they are fine here. I am going to make an aluminum trans cradle, so i'll play around with spindle location. I have to shorten the aluminum swingarm about 2". So far it's going good.
 
Thanks for showing it off as it happens, we all await to gawk at it in new wonder.
 
1973 850 Mono shock / showa forks.

It really doesn't matter whether it's a monoshock or conventional setup. It's the angle of the shock that will cause the problems on a Commando due to the iso's. It's a cantilever. The top is in compression and the bottom is in tension. The ratio between the vertical force at the axle and the loading at the shock pickup point and the swingarm is defined by the angle. The more narrow the angle, the higher the loads. If the frame is as strong as hell between the shock pick up and the swingarm it's not a problem. The problem is the iso's, they get preloaded by the tension on the swingarm which negates their ability to do what they're supposed to do. Even the stock laydown shocks aren't totally innocent, but the effect goes up geometrically with the angle.
 
I am contimplating mounting the swingarm to the frame. I have to go stare at it and figure out how well that will work. That would make the Iso's only have to work the engine/transmission package. My only concern is chain tension, eaven that is slight concern.
 
ludwig said:
When bwolfie's bike hits a bump , the wheel moves up ( force 1 ) it compresses the spring with force 2 ( 2 X force 1 ). The reaction force 3 will pull the swingarm back , or in case of a Commando , it will pull the entire subframe against the limiting rubbers in the isos , or about 5 mm .
Click to expand...

Excellent explanation, thanx.

Can you determine the effect of using a rising rate linkage that redistributes the forces in other ways/directions?

I sincerely appreciate your analysis and would like to see/hear a similarly phrased explanation of THIS system:

1973 850 Mono shock / showa forks.


Thanx (and sorry for the thread hijack, but you may use this rising rate link design, wolfie, if you think it is a worthwhile implementation based on ludwig's and others' input)
 
I am thinking about the rising rate design also. I am looking for all input, so I can make an informed decision. That is the whole point, open discussion. Everyone has their way to do things, none are 100% perfect, but put pieces from each together and things get better.
 
What is the offset on the yokes from the GSXR? I've talked to some people that have swapped in modern frontends who said they really liked how it affected the handling with less offset, more trail.
 
bpatton said:
What is the offset on the yokes from the GSXR? I've talked to some people that have swapped in modern frontends who said they really liked how it affected the handling with less offset, more trail.
Click to expand...

I generally like to use the trail figure for the MK3 850. It is about .3 more than the pre MK3 bikes and really improves the stability. If you go much more than that they get shaky again. Jim
 
I am such a chicken... while redoing my Commando I was tempted to go the upside down and different swing arm way (not mono shock...I do not really care for the look) and, when I saw the bare frame, how flimsy it is, I chicken out thinking that adapting more rigid parts to it will certainly end up with some extra fatigue, ceacks and death of the Isos... Looking at what you are doing I now think that, maybe, I was wrong!!!
Or was I???
Philippe
 
I have been very happy with the improvement the inverted forks made on my Commando. The only other frame mods are the rod links at the head and front of the engine. While it is not as stiff as a modern sportbike it certainly made for a confidence inspiring ride. Jim
 
The commando frame looks frail, but with a few simple improvments it is quite light and strong. I am goung with the forward and head rose joints. And an extra brace between the front tubes. I went to the local bearing shop this morning and ordered tapered steering head, front hub bearings (that will allow the use of the GSXR axle), gearbox inner bearings and outer cover needle bearings and seals. I should have the front end attached within the week. All but the new front hub. I'm working up an order to RGM right now (About $1600 worth). They have a dual disk hub for $125USD. I'm also ordering a belt primary with alloy clutch center and pressure plate. Some engine internals, 850 std liners, Hollow steel pushrods, 2S cam, Ti valve spring top collars. Double sided SS trand adjuster, Needle roller clutch improvment and possibly a Dave Taylor head steady. So far I have sold about $470 of my unused parts, with lot's more left to sell. I also have to order my Aluminum and get my trans cradle and forward engine mount made. If anyone has time look thru RGM's catalog they sell a SS battery tray and aluminum trans cradle and forward mount. It's out there people.
 
when I tried to buy the craddle and front iso mounting from RGM, I received, after 2 weeks and the CC already debited, a short note saying that it was not available and they did not know when they'll make more... Not my idea of a great supplier (I must be badly trained by CNW!!!). I ended up nickel platting both stock parts (no polishing before). Philippe
 
That is part of the reason I'm making my own, being unsure of supply, and to keep the cost down. I ordered my aluminum, i'll pick it up tomorrow and get started on the cradle and mount this weekend. Hopefully in 2 weeks I can have a somewhat roller. At least the major suspention stuff.
 
Concerning the rear suspension: how about attaching the "fixed" end of the suspension to the engine cradle, either above gearbox or below (in a position like on the old guzzis (or even Buell, I think?))?
 
ludwig said:
bpatton said:
What is the offset on the yokes from the GSXR? I've talked to some people that have swapped in modern frontends who said they really liked how it affected the handling with less offset, more trail.
Click to expand...

It is not automatically so that a fork with less offset results in more trail ( in an 850 )
The STD 850 setup is so that the fork legs are not parallel with the steering stem , but about 1.5 ° steeper , thus creating more trail .
A replacement 'parallel' fork , with less offset , may have less trail .

850 setup ( exagerrated ..) :

1973 850 Mono shock / showa forks.

( the fact that the steering centre line seems to go trough the wheel spindle is accidental ..)
Click to expand...

Ludwig, It is only the mk3 850 triple clamps that have the 1.5 degree de-rake to increase the trail. Earlier 850s are parallel. Jim
 
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