The rebuild of my 1974 mark 2a 850cc is for the most part going well if slower than i would like (dont they all). During the rebuild some old accident damage has been found few small dents in tank that where hiden underpaint, both riders footpegs bent upwards alittle, more allarming was the splade bottom yoke with one fork clamp 20 thou closer to the stem hole than the other. The forklegs are straight so must have been change during the post accident repair years ago, i bought the bike from afriend who rode it last in the early 1980s not knowing about this damage and he says it rode straight with no hands a handled ok or he would have not kept it and to this day he is very fussy about ride and handling of his bikes so new bottom yoke seems the worst of it. I now notice the swinging arm is about a 1/4 of an inch closer to the left (drive side) frame rail than the right where it passes it near the Z plate mounts. The wheels and others parts look to line up ok and nothing was hard to fit that would make me think (hope and pray) it is ment to be like this as I know engine and gearbox are offset to line chains up so is this ok or not??? I notice from parts book and pictures of ones for sale on ebay the swinging arm has bracingwhere the short cross tube joins the two longer arms but mine does not and is simply three lenghts of tube is this correct or is it the wrong arm according to the frame number on the V5 (1106**) i beleave this to be an Itailian made frame but has it been repaired with the wrong arm ??? I look forward to your answers and hope they dont mean taking it all apart and starting again Karl
The cradle, front mount an…
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Sounds to me like your swi…
Sounds to me like your swinging arm is from a 750. Mine is a 1970 and has no angled bracing across the corners. The later bikes have the bracing and the Mk3 item is completely different and uses a much larger diameter tubing.
When talking about engine offset, if the engine is 3/16" offset to the left (as it should be) then there will be a difference of 3/8" between the spacing on one side compared with the other. (engine/iso plates to frame lugs)
Yes?
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When talking about engine…
When talking about engine offset, if the engine is 3/16" offset to the left (as it should be) then there will be a difference of 3/8" between the spacing on one side compared with the other. (engine/iso plates to frame lugs)
As David says; the offset is half the difference side to side so my headsteady figure above is 1/8" and not as I said.....corrected!. So, just on my bike the offsets of the various mountings are all over the place which despite my efforts is why it has always had a coarse vibe thru the footrests and gearlever over 4000 rpm. With loose ISO's at 010"/012"it's ok but not turbine smooth like some i've ridden. I've been through the squaring off of ISO tubes, equalising offset etc. (home made rod end headsteady), shims in front ISO but other than improved steering I can't say it made much difference.
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The cradle, front mount and head steady are unofficially offset to the left by 3/16". Mine is about 1/4" as you have measured. I say 'unofficially' as I've not seen any drawings so the 3/16" usually mentioned is likely the nominal and can vary quite a lot. On mine the front ISO has 0.060" more offset than the cradle (rear ISO) at 0.31". A spacer washer is now installed on one side and 60 thou machined off the other end of the tube. It now slides onto the engine and between the tabs quite easily. Before, I had to force the mount in place. The bike used to steer left. It now rides straight. I am told that on Mk3 the swingarm is built to accomodate the offset and therefore the wheel is centred in the rear forks. I have measured 3 non Mk3, including a braced 850 and they are symmetrical. If yours is the the same then the wheel has to be offset 3/16", 1/4" etc to the right, making sure the front wheel is centred in the forks. The offset,I am told, is for tyre to chain clearance. It makes sense. Measure your headsteady centre hole to the sides and see whatit shows. It will give you an idea. Mine is 1.375" R and 1.125" L. So 1/4" offset although the headsteady has less control over cradle/swingarm position than the main ISO's. At least if all three offsets are the same and the frame tabs are welded equally and the frame and swingarm aren't bent you have a fair chance of getting it to ride nicely.
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