75 Mark III refurb/mod project

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If left as-is, the chain would cut a groove just about the size of itself in cross-section, at the bottom of the swingarm's stroke. Once it was compressed to the top, that interference would be less than half that amount. The problem is, that I would need to cut half way into the pipe to allow for the chain guard to clear as well. I think it would be stronger to re-route that leg with a jog at the top, than to chop out a segment and weld in a piece of angle iron bracing around the chainguard (although that would serve as a nifty mounting point for it)

My Dreer-designed unit just clears the chain by a tiny amount, with no provision at all for a chain guard.
 
I suppose the vernier isolastics could be adjusted a bit, but not nearly enough for 1/2" clearance, more with the chainguard...
 
I wish I could see it. You can move a rear wheel and sprockets but I can visualize much tolerance with the drive sprocket on the tranny. It's kind of a decision as to how much is practical, you could move the output to the other side but the cost would be silly.
 
"no thank you" on the 'Silly Cost' idea!

I'm working it out; my oldest brother (mechanical/electrical engineer) is more mechanically inclined than our structural/architectural engineer brother, he's working on it. He's a home-builder of aircraft (Flying Squirrel), so he's studied up on his mechanical structures...
 
The main load on the that tubing on the upper left side is compression. The stock swingarm tubing is way strong enough to afford a divot with a curved plate welded over it. Or you could just cut that whole section of tubing off and put in a bent piece.
 
On second thought, probably nix on the divot idea if it's half the diameter of the tubing. Honestly, using the stock swingarm for the upper section is overkill. You could use lighter tubing there and get a piece bent with a slight S to go over the chainguard. I don't think you can use the iso's to move things around because the swingarm's going to move with it.
 
Most times if it looks right it is, even without engineering.
I would think the original swingarm would be the main structural piece, and the upper section could be of a lighter material.
This upper piece, while having to deal with the loads of the suspension, could have offsets in it to suit the chain clearence problems.
While a bit off the subject, ducati did similar offsets and lighter tubing for canterlever and rising rate. The shock mount at the top is offset to clear the rear carb. They used alloy or square or round chrome molly tube.

IMG]http://i579.photobucket.com/albums/ss232/GRM450/TT31-5-08005.jpg[/IMG]
 
That didn't work, I'll try again.

75 Mark III refurb/mod project
 
My eldest brother replied in the affirmative as to the cut-out notch with a section of angle iron to reinforce that segment. The actual cut-out, in section, is less than 1/3 of the diameter of the tube (at it's deepest point) , and less than 3" long. Indeed it is way over-designed and will be structural overkill.

75 Mark III refurb/mod project


My main purpose in using a second swingarm was many-fold: 1. I had a spare laying around, 2. It fits in the available space perfectly, 3. It made designing and fabricating the main pivot mount for the rising-rate linkage a "done deal" by simply fabricating a set of bushing blocks to fit the existing swingarm bushings, 4. Fabrication work is cut in half, 5. Integrity of the existing welds is very good, 6. The Dreer-designed unit has some shortcoming that are going to require additional work on my 880 to produce a satisfactory finished system, and 7. The Dreer swingarm also required custom fabrication of a new rear axle, spacer, and chain adjuster blocks.

Net result should be a better system at lower cost. Some may like the "trick look" of the rectangular-section tubing of the Dreer unit, but I think I prefer the "beefy look" of my unit.
 
All the pieces are ready, I'll have the welder form perfect saddles on the two uprights and tack everything together, then mock it up on the bike and test range of motion. I'll also be marking the notch for the chain, and have them cut it and weld in the angle iron brace. While I can "stick weld" acceptably, I want the finish on this piece to be as near perfect as possible. Next stop will be the machinist to have him cut the two pivot lugs to fit a set of standard swingarm bushings for the rising rate linkage pivot rod (a bit of overkill).
 
Disassembly started yesterday; start with removing the exhaust to set it on the lift-
75 Mark III refurb/mod project


Tank, seat & sidecovers off-
75 Mark III refurb/mod project


Rear fender, meters, handlebars & controls off-
75 Mark III refurb/mod project
 
Rear wheel off-
75 Mark III refurb/mod project


Left footpeg & z-plate, rear sprocket assembly & chain off-
75 Mark III refurb/mod project


Primary cover off, so far no suprises whatsoever-
75 Mark III refurb/mod project
 
Primary system removed WITHOUT PULLERS!
75 Mark III refurb/mod project


Right side footpeg & rear brakes removed-
75 Mark III refurb/mod project


Not sure how many miles this doll's shoe has on it, but it fell out from behind the Z-plate...
75 Mark III refurb/mod project
 
Got a call from the welding shop just before lunch...
75 Mark III refurb/mod project


Time for a working mock-up to test range of motion.
 
I'm going to shift gears a bit and move progress over to the "test mule" parts bike that will get this prototype monoshock setup and a '74 850 engine.

Meanwhile, the client's stuff will get thoroughly cleaned and the top end job will commence sometime in the next week or so, once I get the monoshock completely welded up and have a rolling test bike.

Conveniently, I have these two, as well as the other client's N15 hybrid that will all enjoy discounted pricing on powdercoat, paint, chrome, polishing, parts shipping, etc. It's always nice to take advantage of volume discounts, this time all three are Nortons!
 
One thing for sure, the head was WELL TORQUED! All of the fasteners gave a healthy “pop” when they broke loose, then screwed out cleanly by finger, very nice.

Typical carbon buildup, maybe a bit on the heavy side. Pushrods in decent shape; one has a “polished” area, maybe I’ll re-work the pushrod tunnel a tad to give a touch more clearance there -

75 Mark III refurb/mod project


Copper head gasket is in decent shape; pistons have a good bit of buildup –

75 Mark III refurb/mod project


First point on the “disappointment” list – connecting rods are nicked from top to bottom, all the way around; I think something was adrift in the crankcase, rattling around for a good little while –

75 Mark III refurb/mod project
 
Cylinders were in decent shape; they’ll go first oversize with no worries –

75 Mark III refurb/mod project


Pistons are .std, but worn out & beat up –

75 Mark III refurb/mod project


75 Mark III refurb/mod project


Whatever was floating around in there did some damage. Cases will have to be split no matter what; cam has to go at a minimum.
 
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