Last time I rode it all was running well until approaching a T junction after brisk acceleration I went to pull in the clutch and it was rock solid . There was no warning of this symptom, it just happened. I nursed the bike home with clutch-less changes and on trying to restart it found the kickstarter no longer engages – doesn’t seem to be connected to anything now.
Any ideas on what has happened?
minetymenace wrote: ↑Mon Jul 20, 2020 8:14 am
And I'm not the only one beat!!
Yep ! ..... flat out in top on the old B50 across the field when it all locks up. Longest rear wheel slide I have ever done. Managed to stop before hitting the hedge.
The gear had welded itself to the shaft and locked the lot up. I had to get the angle grinder out to remove it.
It may not be as bad as the doom and gloom merchants (including me) have predicted, whip the timing side cover off and take a picture of the contents or gloop....
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
minetymenace wrote: ↑Mon Jul 20, 2020 8:14 am
And I'm not the only one beat!!
Yep ! ..... flat out in top on the old B50 across the field when it all locks up. Longest rear wheel slide I have ever done. Managed to stop before hitting the hedge.
The gear had welded itself to the shaft and locked the lot up. I had to get the angle grinder out to remove it.
Kickstart not returning to its "disengaged" position, possibly weak kick start return spring, cases not aligned, some binding bearing surface, return impeded by boot or leg etc...
If the kickstart pinion is the held still by the rack on the quadrant, as the mainshaft is always spinning when the engine is running (and clutch clutching, flux capacitor fluxing etc) the poor little bush starts to get hot as it pines for a splash of oil which alas, is an inch or two below. Friction welding is a well known technique...need I say more?
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
It was (as Gerry said) a friction welding issue. This was when I first had my B50MX many years ago and was not familiar with the foibles of BSA engineering !
I rebuilt it with all new parts and it never gave trouble again. Having said that, I sold it about a year later to a nice man in Japan. Did it last ???? Who knows.
The CCM on the other hand has never given any trouble whatsoever (touches wood !). I have been racing that for probably 15 years plus.
Today I tried to remove the timing side cover and guess what? Just as expected 3 of the screws that were already a bit mashed up won’t come out . Two at the top, one tight at the bottom. I tried a gentle chiselling but didn’t want to destroy the heads completely. I don’t have an impact driver so I suppose the next step is to buy one, although I’ve never had much success with them in the past.
An impact driver is really your best bet. Just make sure the bit you use is the correct one for the screw you are undoing. Give it a "prime" and then mate with a BFH. Replace them with cap head bolts and all will be good.
Finally managed to remove the three remaining screws having got an impact driver and got the cover off. Inside was a lot of swarf that has come from the clutch lever actuation area, which is why the clutch lever was frozen.
The starter pinion spins on its shaft but doesn't turn the engine. I'm not sure what's happened here.
I'm going to do that but I’m still waiting for my son to get his staff discount card from Wickes.
In the meantime, I suppose have to get a new outer timing casing to replace the mangled one, but there don’t seem to be many advertised and those I’ve found are out of stock. I was going to go to Kempton but that was cancelled. Alternatively, I might just reassemble it all and sell it as a non-runner which would be a shame after all the years I’ve had this bike.
How interchangeable are these casings? The parts book gives different part number for each year 72 & 73, mine’s a 73 according to the engine number.
The major difference is where the points wire exits, but clean up your old one first, despite the swarf it may be OK. I's investigate why it made the swarf in the first place, that nut doesn't look like it is on all the way, how much end float do you have on the mainshaft? Has the clutch fallen off?
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
The pinion gear on the end of the mainshaft is a 2-gear affair where the outer gear under the nut is fixed and the inner gears spins freely on a steel sleeve with a light spring that keeps it engaged to the outer gear. The teeth are designed to grab when the kickstart is actuated and release as the kick start arm returns to its starting position. It looks like the kickstart spring has already been welded once and was probably not strong enough to keep the kickstart lever from self-actuating, especially going over jumps and bumps. When that happens, the kickstart quadrant tries to engage the spinning mainshaft gear resulting in stripping the teeth off that fixed gear. Looks like all the teeth have possibly been removed in this fashion so the two gears no longer engage each other, hence your ability to spin it without turning the mainshaft. The swarf is probably the remains of the engagement teeth on that gear. Some of the swarf may have gotten into the clutch release rack and pinion. You can remove the gear from the clutch arm by rotating the arm backwards with the rack in place (left hand threads). It may not be ruined.
The outer timing covers are pretty much all the same so if you can find one off any unit single, you just need to drill or mill a slot for the ignition wires to exit the points recess or electronic pick-up if you have one. Also, since the non-B50 have a hole into the inner timing cover, you may want to seal that off with silicon. You can just drill the new hole and seal it with silicon if you don't mind the look of it.
Without having it in front of me, this is just speculation. Let us know what you find.
Oh, I think (but not sure) that the later B50 style outer cover is different to the earlier ones (my 250 has the later one). The difference is in the gearbox mainshaft, the later ones have a ratchet that is the other way round meaning the quadrant and ratchet mechanisms are different and I think there is a corresponding difference in the outer cover too...but not sure.
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
Thanks for the input guys, and Tom you are quite right about the weak spring.
The kick-starter always flopped at the top of its travel which didn’t help with starting as getting a full kick was never possible. Another feature this bike always suffered from was freeing off the clutch before starting which was always difficult even though the adjustment seemed to be fine. When I looked through the seller’s Ebay purchases he had bought some clutch tool so it clearly had some work in that area before I bought it.
I’ll delve deeper when I get the time and report back.
MM already mentioned this, but he asked if the nut was tight. I forgot to mention that if the nut comes loose, the gear rack cannot push the clutch release rod and you will get the exact same consequence - - the clutch will feel rock solid as it hits the nut before it contacts the rod. Also, quite simply, if the adjustment nut (primary side) loosens up completely, or the rod is too short due to previously welding and breaking loose, the same thing will happen. When you said you can spin the kickstart gear without turning the mainshaft, it could also be because the small spring behind the gear has broken and the gears are no longer in contact. It's the outer gear that turns the mainshaft.
Tom
Thanks Tom, the nut is tight which is why I need an impact wrench that I still haven’t sourced. I have however bought a replacement casing off Ebay. This, like a lot of such purchases has turned out to be a disappointment where some clown has had a go at polishing out all the deep digs and scratches unsuccessfully that didn’t show on the photographs. I can live with that for the time being but all interest in this bike has waned and I don’t expect to look at it again until next spring/summer at the earliest.
I’ll also buy a new kickstart spring, why would anyone weld it up when they are only a fiver??
Hi, from what I can see in the first picture, the nut on the mainshaft/kickstart ratchet gears is definitely not on correctly, it may be tight, but probably because the thread of the nut or shaft is damaged. When the shaft and kickstart ratchet is assembled with the nut and tab washer and tightened up, it goes all the way on and the mainshaft will come through the nut and it will protrude approx 1 thread past the nut.
If you want to see it assembled correctly I can send you a picture later, but what you have there is a kickstart gear/mainshaft nut that has worked loose and chewed itself into the outer cover, and that is a definite, because my engine with it assembled correctly doesn't have the nut as yours is in the picture.
Ian Hingley wrote: ↑Mon Aug 10, 2020 9:59 pm
Is the nut on the end of the mainshaft tight?
Ian
Maybe I should have said 'fully home' rather than just 'tight' when I commented back in August. I agree with hb123 (hi Jon) that this looks exactly like the mainshaft being able to wander and for the nut to foul the outer casing. Experienced it myself many years back. Of course.
The photos are very useful HB123, thank you. My tab washer is ripped and it is clear the nut is not fully home compared to yours. Hopefully more will be revealed once I get it off.
. There was no warning of this symptom, it just happened. I nursed the bike home with clutch-less changes and on trying to restart it found the kickstarter no longer engages – doesn’t seem to be connected to anything now.
