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This can be done on all 650 models  from 1950 to 1972.5 and therefore 500 models from ’50 to 60 as they used the same box. Half way through 1972 the factory started fitting 5 speed gearboxes to their big twins and triples. It is fairly easy to fit the 5 speed cluster, the hard part may be to find one. Try and find as complete a cluster as possible. The early 5 speed were considered a bit fragile although I have one in a late 1974 bonnie and other than having to loctite a bush in place I have had no problems. They are fine for touring and general use. Just make sure to free the clutch plates before engaging first or pulling wheelies ( do you still do that). The clusters look pretty much the same but all of the layshaft set is not interchangeable with the strengthened later cluster .The mainshaft and gears are fine. The problem lies with mainly the layshaft  1st gear engagement dog breaking from smashing into first and the narrow first edition layshaft top gear which is responsible for transmitting power for the first 4 gears to the output hi gear . If you find a triple set that will be fine but you will need to buy a twin mainshaft. See pic 1, very noticble eh.

So, after removing the primary drive and clutch ,pull the kicker cover and so on until all is revealed. Put it all to one side, nothing interchanges. Get your butane /MAP gas and warm the area around the main bearing after removing the seal and circlip. From the inside tap the ball out. Do the same to the ball bearing in the inner cover. Both these areas need metal removed so get the dremel and after marking how much , take it easy. The hi gear hole needs to clear for the hi gear to fit through. This is about ½” wide so about ¼” will need to removed . The bearing in the cover can go back in if in good condition but material needs to be removed to clear the nose of the mainshaft 4/5th paired gears as it shoulders up to the bearing when tightened. When done and cleaned of swarf, heat cases again and fit bearings,  circlips and the hi gear seal. Take the quadrant from the inner cover and fit the 5 speed version. Try fitting the cam plate in and if a full round one may need some minor dremel work to freely swing 360 degrees. Also the 4 speed camplate spring holder may need to be shortened if a correct 5 speed one didn’t come with your gearset. Before you fit the hi gear fit a new seal and also the camplate especially if it is the full round type. Don’t forget the 71-1070 ‘O’ ring under the lockwasher or plenty of sealer if the early type to prevent oil leaking down the sprocket spline. If the Torrington needle rollers  B1112 and M11121 are good then leave them. If a pre-unit then fit thees Torringtons in place of the bushes and pick up some layshaft thrust washers . I always fit the cluster in with the camplate (in 1st gear). Fit the mainshaft and 4th gear with selector and as you try to drop the round selector follower into the camplate groove, push the cam plate up slightly , then let it drop, the selector will then stay in place. Fit the layshaft with next 2 gears and selector making sure thrust washer is greased and in place on it’s pin. Same procedure , pull the camplate down slightly to engage selector follower pin into camplate  groove and release. Then fit other main and lashaft gears. With 1st gear layshaft the same applies , move camplate slightly . Fit the selector shaft through all 3 selectors and the  circlip between the 1st gear and it’s dog ,then the dog. At this point after fitting a gasket and the thrust washer with grease offer the inner cover up. As it nears the dowels feel with your thumb on the quadrant, lifting ever so slightly for the teeth to engage and tap cover home. The quadrant on the inside should be about up about 1/16” from hitting the alloy and be free. Fit 2 diagonal screws and lever with biggish screwdriver downwards, spinning the shaft and sprocket output , feel for neutral ,2nd etc. If happy after a few runs through at this point I like to fit the sprocket and rear chain and then the rest of the primary but not the cover yet. Use the screwdriver th lever through the gears again. If all good fit the kickstart ratchet gears and lock the wheel and tighten it is ok to lightly rattle the nut but only of the clutch is not complete and the shaft can spin . It could break the thread off the mainshaft. Take the plunger body from the outer kicker cover and replace with correct plunger body and 5 speed plungers. If you have the 4 speed parts in this cover it will not shift correctly, might as well fit 2 new return centralising springs , the banana shaped ones. Then fit this cover and use the gear lever to shift through the gears, turning the back wheel. Then set your clutch pressure and run out before buttoning it all up. While you are there dress the steel clutch plates on some emery paper on a flat plate , if you have at least 70-80 % surface area the clutch will be perfect . Never wind the clutch spring past the end of the screwed pin thread. With more surface area you can back the screws off some to attain a 2 finger clutch with no slip. Adjust the push rod after slackening the cable allowing the clutch mechanism to centre in the kicker cover. Take up and with your nose pickin  digit, feel for free play, a smidge or a smidge and a bit is fine, about ½ to ¾ turn at the adjuster,  lock the nut then take up cable slack, leaving a bit of free play at the lever. I use 89-90 gear oil and if an early model I use auto trans fluid in the primary. The fiver is a very modern shifting gearbox and as you will have noticed has only 3-4 dogs to engage instead of the 4 speed spline type of 23 + teeth to mesh.  So you may have also figured that the reverse is possible and fair enough as the 4 speed is mostly a tough cluster , I am using 3 out of the 4 in my dirt dragger,  and also, fitting the 5 speed to a 4 speed Trident or Rocket is the same .   Happy trails.


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