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Dick Harris
Dick Harris
East Bethany New York
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T100c jumping out of 2nd and 3rd
#803828 04/03/20 7:33 am
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Hi all,

Plenty of threads about jumping out of third gear, but I've got 2nd and 3rd jumping higher up the rev range.

Is the solution still the same, shim main shaft and stronger selector pin spring?


Cheers

Richard.

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Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803829 04/03/20 7:55 am
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Sliding gear gear dogs?
Cam plate?

Hard to say.

Last edited by NickL; 04/03/20 7:57 am.
Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803831 04/03/20 9:32 am
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NickL +1 , box open to inspect job. also look at the shifter forks and the grooves they engage with on the sliding gears.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803832 04/03/20 9:50 am
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cheers chaps, you're right.

I'll take it out and have a look.

It's not going anywhere soon at the moment anyhow.

Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803842 04/03/20 1:02 pm
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Frogeye1000 - ok, fires out of gear at high revs, but WHEN? Right after shifting up? After shifting down? When it's been running ok in a gear and you accelerate or go up a hill?


Bruce Miller
aka The Hermit
The Bonnie Ref: https://www.hermit.cc/tmc/om/manual.htm
Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803891 04/03/20 10:11 pm
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It will sit in second or third no problem until I accelerate, then when i'm higher up the rev range it will jump out..Doesn't matter whether I'm shifting up or down. It does seem to do it a bit less when warmed up.

When it jumps out and you put it back in again and accelerate, it will still jump out again.

Have been changing up through the gears slowly until 4th to avoid jumping.

Cheers

Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803894 04/03/20 10:40 pm
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When you find some real HP with the 500 transmission, and/or run it up the rpm range to where the factory ran their 500 racers (8,000 +), 3rd gear will eject engagement with enough explosive power to blow the circlip, that retains the main shaft k/s side bearing, into the outer cover.

Most of the problem that causes this is the camplate. It doesn't move the male dogs on the sliding gear far enough into the female dogs in the mating gear. This can be improved by shiming the main shaft between main shaft first and the K/S bearing. It takes approximately 0.025" with FINAL checking to make sure the faces of the two gears do not touch.

They knew this was a problem when they put the bridge across the 3rd-4th camplate track. Without the bridge the outside edge would deform from the pressure making things worse. So if you have a camplate without a bridge you should replace it.

The tracks in the camplate will also suffer when the gears blow out of gear. Any problems in the tracks will be evident upon inspection.

If experience prevails you will also find have that you will have to replace both the sets of gears for 2nd layshaft and 3rd gear mainshaft.

A less common is the circlip that retains the K/S side mainshaft ball bearing. Early models it was as thin as the circlip used in the front wheel. Later models the circlip was about three times as thick. Good you say! The problem is it made the casting that supported the circlip thinner. An explosive 3rd gear disengagement would leave the thin bit of casting retaining the circlip, and the circlip, in the outer cover.

For racing we just removed the circlip, welded a "top hat" where the circlip was and machined off the casting on the inside of the cover so the bearing could be replaced. this actually helped with the 3rd gear problem more than other things we tried. This left the bike without a kick starter...

This is one reason Tim Joyce cut his 500 transmission off his 500 and welded a 650 5 speed onto the back. When you really find some HP with the 500 you have a very narrow power band, and the extra gear was help full in keeping the bike in the power band. I have heard of some UK 500 racers who stuff the 500 crankshaft into a set of 650 cases and run a 500 top end. Haven't seen one though so I don't know if it just a story.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803901 04/03/20 11:21 pm
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It's hardly surprising really, that box design started in the C15 or was is the cub/terrier and was used up to the A70.
Racers with A65's went through similar problems, although mainly related to mainshaft flexure. The attempt at
a cure with the bridged camplate was ineffective there.


It works chaps, just make it a bit bigger eh?

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803933 04/04/20 4:37 am
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Yup, this problem was my first introduction to the wonderful world of BSA. No fun in the mountains when it keeps popping out of second gear. Ended up replacing 2nd and 3rd because the dogs were worn.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #803943 04/04/20 8:54 am
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Thanks for that john. Very informative. I'll update progress when I've got gearbox out.

We're not allowed out here in UK at the moment , only for work if you're a key worker, so plenty of time.


Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805182 04/13/20 3:30 pm
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Hi chaps,

Bit of an update. I've removed inner and outer gearbox casings. Camplate looks worn and the follower on one of the selector forks was missing its securing washer on top. Also there should be a shim washer between the kick start shaft and the inner housing. Bush on the gear behind the kick start worn. The dogs on the layshaft gear are a little worn so I presume the one on the main shaft is too.

Plan of action is to replace worn camplate , selector pin, gear bush and missing washer. Nip up inner casing, select third and measure end float on main shaft before fitting nut then shim the inner side of main shaft with a shim washer leaving a few thou clearance so the dogs don't bottom out.

This I can do without removing clutch, which I didn't want to do, but if it doesn't work I may have to to get at the gears.

https://photos.app.goo.gl/s6PFaYGJnP8kZojw8

https://photos.app.goo.gl/6qFdA4ndbrazi99U9

https://photos.app.goo.gl/9LQ5UBHzGdFR2c1dA

Cheers

Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805188 04/13/20 3:51 pm
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Richard there is no washer between the kick starter quadrant and the inner gearbox cover. There is a shield (very thin washer) inside the first gear that keeps the kick starter pawl from catching on the first gear female dogs (holes).

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805193 04/13/20 4:01 pm
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Thanks john, my mistake. Wherever it fits its missing. As is the spacer on the front behind the spring.

Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805210 04/13/20 6:44 pm
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It may be worthwhile buying new gears and having the dogs "back cut" This gives the dogs a slight dovetail shape. Race gearboxes are back cut, as the power is applied the shape of the dogs pulls them closer into engagement


BSA B31 500 "Stargazer"
Greeves 200 "Blue Meanie"
Greeves 350
Greeves 360
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500 sprint/LSR bike "Deofol"
Jawa 500 "Llareggub"
Aprilia RSV Mille "Lo Stregone"
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Re: T100c jumping out of 2nd and 3rd
Andy Higham #805239 04/13/20 9:37 pm
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Originally Posted by Andy Higham
It may be worthwhile buying new gears and having the dogs "back cut" This gives the dogs a slight dovetail shape. Race gearboxes are back cut, as the power is applied the shape of the dogs pulls them closer into engagement


Snag with hat is the hardened surface is very thin. Also the design of the female gears makes that job very awkward.
Unless being used on the track a well set up version of the 500 box will last well. It's only when you start racing them
that those sorts of mods become a must.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805240 04/13/20 9:44 pm
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No it is a thin shim that goes inside the first gear sitting over the holes. It keeps the ratchet from fouling in the holes.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805251 04/13/20 11:14 pm
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Parts 57.1426 and 57.1464 (19 & 45 in the parts book) kick start pawl disc and kick start spacer.. I misread where the disc went.

I don't think there's any need to undercut the gears. It only comes out on a Sunday if the weather's fine and doesn't get hammered.

If it still jumps when it goes back together then I may try dressing the dogs up a bit on the mill before I take the plunge and order new gears.

Cheers

Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805405 04/15/20 12:23 am
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Hi again,

quick question, is there any way or need to shim the layshaft away from the clutch side needle bearing to better engage the dogs on that shaft. if not is there anything that can be done other than buy new parts?


cheers

Richard.

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805435 04/15/20 12:05 pm
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But don't forget that when you shim the mainshaft you must realign the primary chain!!

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #805493 04/15/20 10:13 pm
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Cheers john. Got that one covered. Have a box of assorted shim washers.

Is there anything that can be done to the layshaft to make the gears engage better?


Richard

Re: T100c jumping out of 2nd and 3rd
Frogeye1000 #808872 05/14/20 3:15 am
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quick update.

fitted new 2nd and 3rd sliding gears along with new cam-plate ,index plunger and lay-shaft bush. also fitted a 20 tooth sprocket.

there was little to no play in main-shaft when third gear selected so decided not to shim shaft out.

gears select good with no jumping out. have a slight issue with the gear lever not returning sometimes due to the selector plungers sticking with the new cam-pate and needing a slight tap with the foot.

cheers

Richard.


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