Mech

And in that regard.. trust your fingers. Fingers can detect distortion and bumps in the range of fractions of a thou.. Your eye can't see a bump or distortion of five thou generally/often.. I've trained apprentices and the best lesson you can give them is to use all their senses. It helps hugely in their manual work, and in diagnosing.. I have heaps of small stones.. I make swords.. haha.. They are slow, but they will do things that neither files nor grinding tools will/can do. A little kerosene and press hard and move slowly to grind, when you want to polish the surface, then light and faster.

So it is hard then.. I'd probably use an oilstone.. but I'm a bit strange.. haha. I doubt the sliding dog gets right to the end of the shaft. As long as you can get that dog on and off the splines it's probably good enough. It's not going to stick or fail to engage or anything. I'd want the running surface for the bush to be nice though..

I think it will have been a steel backed white metal bush.. Thin layer of white metal so it doesn't squeeze out under pressure. And yeah, the pattern would have held oil. Although it is fed oil under low pressure, it wasn't designed to float on a layer of high pressure oil like a main or big end is in a car. Every part in there is the result of more than a century of accumulated knowledge and refinement.. And the Japs are really good at that !

Ha.. ok.. for $12 yeah.. Hopefully everything else you need will be availiable at a ok price. You were lucky about the stator !!

Yeah that bearing would have got pulled up out of the side case by the shafts being cocked over in the bearings.. and the tapping and wriggling. And yeah.. I was wondering if perhaps that shaft isn't slightly soft at the end there where the bush runs.. On purpose. Check it with a file out on the end where the bearing sits. Yeah I'd file or oilstone all the burrs off, get new washers and check/calculate the end clearances using a straight edge and vernier calipers. The bush, engineering supply shops have stock bushes, in various materials. You will probably need a brass bush, unless they have some fancy new suggestion, like teflon(not teflon.. it's too soft), but try not to get sold sintered bronze, which is porous and soft and isn't really suitable. Sintered bronze is what lots of old starter and generators used to use, the bushes are obviously porous.. Brass is shiny and not porous. Sintered bronze would do at a pinch, but I'd want to take it out when I had a recheck in there after a few miles. Anyway.. They come in standard metric and imperial internal and outer diameters, and various lengths. If you are lucky you will find one that has both the inside and outer diameters right and only have to cut it shorter perhaps. If not, choose one with the right outer diameter and cut it to length, press it in and then ream, machine or hone it to a nice fine clearance on the shaft.

You probably have a bad connection somewhere, or a dud battery. The bad connection could be on the power wires/cables, or on an earth wire/cable. I think we should get that fixed first, then check the no start. When you push the button and the buzzing happens, does the dash or warning lights go out ? And, if you turn the headlights on and push the button, does the headlight go dull ? Can you tell us about the circumstances.. did it have the buzzing before the carb, or any work, has it been parked up or ridden regularly, have you had it long ? Anything else you can think of to tell us about it's history ?

Yeah I've seen lcd displays get faded..I think the only test for it will be to ensure it's getting full power and earth, because they are quite current dependent, and as long as it's getting power to the gauge then the conclusion is that the display is dying..

Does it restart easy and straight away ?

Good point Gw.. That is mostly the more common scenerio.. Thinking thinking... I can't her that video.. bad internet.. So it's just running high steady revs is it, then suddenly cuts out ? Carby breather hose blocked ?

Spoken like a true rebel.. Onya Ulf.. couldn't agree more.

I'd check that it was getting full voltage at the power pins, with the gauge connected so there was the usual working load on the connection. If you just check the voltage with the plug disconnected, and there is a bad connection, it can show 12v, but then drop right down(or a little down), as soon as the load comes on. There are probably two power supplies to that gauge, and perhaps more than one earth. I'd check them all..

It sounds like it's going too lean.. Have you checked the fuel flow to the carb is adequate ? The best way is to turn the fuel tap off, then undo the carb drain screw and watch it flow out, then turn the fuel on and make sure it keeps flowing good. Then, with the engine warm, try adjusting the idle mixture. It should respond to a half turn either way, if it doesn't respond to a half turn in each direction(too lean and too rich), then there's a problem in the carb.. Another thing that might cause it would be tight valve clearances.. Unlikely if it has shim adjusters though. Oh.. Tank breather too.. check that too, though that normally takes a while to manifest..

That heat was caused by the end thrust, and should not in theory have worn the shaft's bearing surface. The heat on the gear shouldn't be any problem as long as the new bush fits nice. The heat on the shaft.. Hard to say. You could try scratching the shaft a little with a file on a place where it hasn't got hot. That will show whether it was a heat treated(hardened) surface. If it's fairly markable on an unheated part then it was soft to start. If the test suggests it was case hardened, then you need to decide how soft it is now..

Ouch ! Well.. If that was my bike, or, under the circumstances, even a customer's with their agreement, which they'd all give knowing I'm a responsible(and competent) guy, I'd clean all that up and put it together with new washers and possibly a bush.. possibly. That bush was probably made with the split. If it's worn get a new bush from the engineering supply shop. Then I'd try the bike out for a bit before ripping it apart again and checking how things were looking and what I'd decided the bike needed in the way of other work. It's a small investment in gasket and shim etc and only a bit of time..

Have you seen that there is a service manual section in here ? Top right of the home page there's a button that goes to the manuals page, scroll down a little and choose your make from on the right..

Good one. Thanks for the report back..

No vacuum is a bit strange and you'd normally say cam timing, but you've rechecked that already.. Air leaks into the manifold, or anything that will make it run lean can cause backfires out the exhaust on over-run, and out the carb any time, but mostly as you accelerate. Lean running though doesn't generally cause kick back on the pull start or starter. It can occasionaly, but randomly, because of very slow burning lean mixture still being in there when a new charge of fuel comes in, but it's not a main symptom like it is in this case. The symptoms and circumstances suggest it's bad ignition timing still. Most yamaha have a feed into the cdi unit from the starter. When you push the starter button the cdi unit does something to facilitate an easy start on the starter motor and to prevent kicking back. It may kill the first firing or retard the ignition timing while your thumbs on the button. When you want to start it with the pull start, you are meant to use it with the decomp and so the kickback shouldn't occur. Sooo.. Do you have a timing light Does the cdi unit you have there have a feed for the starter.. Oh, and by the way.. some of them feed 12v in when the starter is operating, and others have 12v going into the cdi and then a wire going out to the start button.. Both systems detect starter operation, but you need to figure which way the bike is wired, and which sort of cdi unit you have.. All that said, that only relates to the kickback.. the short run before conking out is possibly something else, a fuel supply problem perhaps.. You need to watch out that it could have more than one problem..haha.. Not very helpful I'm sure but people get caught out and confused trying to treat two problems as one.. If you have a timing light, check the timing, then try to start the bike and keep watching the timing light, if it goes off while the engine is still spinning over then the cdi is failing for some reason. If the cdi isn't dying, then suss the bikes wiring regards the starter feed, and then once it's starting properly start to figure why it dies after a few seconds.. fuel perhaps.

Hi Steve. It's possible, but then other than too much compression, which should get released by a working decomp, it shouldn't cause a problem that only shows up when the plug is in. If the cam timing was out and two valves hit, then yeah it could cause a lockup, or if one valve set hit the piston, yeah it could lock up.. but then it wouldn't matter whether the plug was in or out.. The valves would hit or they wouldn't.. What we need here is someone that has seen a worn or faulty decompressor that can explain what wears or goes wrong with them..

I've looked in a couple of books and they seem to expect no more than 90lbs if the decomp is working right.. You still haven't confirmed that it will turn over if you leave the plug slightly loose and turn it slow enough for the compression to escape.. That will prove it's only compression and not anythng mechanical.

Have you looked for a vin or frame number ? It might be on a plate, or just stamped into the frame somewhere.. The steering head is a common place.. but they can be anywhere on the frame.

In some of the manuals for those things they have a maximum compression reading listed. Apparently, that's the maximum it should have for an easy start if the de-compressor is working. It shouldn't be higher than that figure if the decomp is working as it should. Have you read what it should be for that bike ? Perhaps the decomp isn't working.. perhaps there is wear..

It could be.. Could you try putting it on a buddy's bike to see if it looks the same, or borrow one for a few minutes.. They only need to be plugged in to try. If you walk into a bike shop they might test it on something in the workshop if you bribe them.

It will just be the soft bush damaged.. wind and pull it.. it'll come. Then use a scraper to touch it up. They likely started out trying to get the switch fixed.. I doubt the magnets were the problem, they got knocked off by them hammering, and perhaps really fell out when you dragged it off.

The gear 4 runs right on the end of the shaft almost, and in the drawing it shows an oil hole to it. Then there's a shim and a bearing. That bush that's splined to the same shaft, part 8 in that manual photo, that has the other gear running on it. Both those two gears are free wheeling unless the sliding, and splined to the shaft dog, is slid along into mesh with one or the other of them. Oh and look.. in that manual photo.. the shaft does have a groove between the machined round and the splines.. Bingo.. That's where the bush is caught Gw..

Looking at your photos it looks like gear 4 has a bush in it.. The shaft and damage shouldn't be too bad. If it won't wind off by hand I'd use a small puller.