I've got a problem..... I wen't just for a ride and suddenly the bike wont get into the 3th gear.... the 1st and 2th there is no proble but the 3th will not work....Dont have any idea what the problem is..... Can someone help me??

Thanks!!

Bjorn

email (option): bsam20@ziggo.nl

Hi Bjorn,

I am sure that other guys on the forum can give you better info about adjusting the gear selector or check the forks.
I have not done it for a very long time, but I do remember encountering something you might consider before getting into any work:

Sometimes if the angle of the shifter lever is too low downwards, it will not go all the way, and stopped by the frame, preventing gears to engage.
Sometimes a shorter way is needed for a gear to engage, so the 2nd gear engages, but not the 3rd.

Worth checking..

Noam.

email (option): noam10@gmail.com

Surely on positive stop box the lever goes down the same for each gear, it would hit frame on all gears.....

I did have one m.box that had the selector linkage put on upside down or adjusted out to much ....& jambed when selecting 3rd.

There is a section on shift linkage adjustment in the Maintainance Manual.

http://www.4shared.com/office/lA-4nux8/BSA-M20-Maintenance-Manual.html

no more than a half- turn on the adjuster rod to shorten/lengthen it, should do it...had exactly the same problem as you describe. Eventually the sum total of all the wear and clearances in the linkage and box come together, leaving insufficient travel to engage the gears.

Hope this works for you.

JDE

email (option): teladelujo@msn.com

Yes, all the gears should go the same way down,
But I had the same problem, and the fact is that pulling one notch up solved it, at least for me..

If the selector was installed incorrectly,
I guess there was no third gear to start with..

N.

email (option): noam10@gmail.com

No, the gearbox i had with the adjuster installed incorrectly worked fine then one day locked in 3rd gear because the adjuster rod was getting bent over at the the end. More & more in use.
It had been assembled by someone who also thought canned food tin metal was a good way to repair worn bushes.

Hi Fred.

Thanks.

I am always happy to learn.

Noam.

email (option): noam10@gmail.com

The problem with adjusting the gear change 'in situ' is that you are making a 'blind' adjustment as you cannot see inside the box to a) clearly identify the cause of the problem and b) see exactly the effect of the alterations. This facility is provided for correct initial setting of the box at rebuild and for minor operational adjustments to a basically sound gearbox but should not be regarded as a 'compensator mechanism' for worn gearbox components or faulty assembly.
If the box was incorrectly assembled in the first place and shimming of the shafts was incorrect or it was incorrectly set up it is entirely possible that it would have selected all four gears but not actually be working as intended.
In that situation wear of the selector dog grooves and/or dogs, selector fork arms and selector fork tracks and pins are all possible consequences that could ultimately lead to a change in the gearboxes operation at a later date.
Wear in the gearbox casing bushes, the bushes in 3rd, 1st. gear and 4th gear(the sleeve gear), caused by poor lubrication (common in a boxes that don't have a sealed bearing fitted) can also have a contributory effect. Damage to the teeth or pawls of the gearchange mechanism could also be a factor..though this is far less common.
If the box hasn't been apart for a long time, has been low on oil frequently or you are unsure of whether it was put together correctly the last time it was rebuilt I would suggest that now might be the time to take it apart for proper examination and remedial work as required ....Ian

email (option): ian@wright52.plus.com

Mr. Wright,

Always the voice of calm and reason....!

The sleeve gear bush in the transmission I am working on is quite worn, but all other componants appear to be in reasonably good condition. From your comment above, I take it that the sleeve gear bush is the first to suffer from low transmission oil levels brought about be leakage past an unsealed output shaft bearing.

Upon disassembly, I found the mainshaft oiling grooves packed with bronze fines in the section that passes through the 4th gear sleeve, which prevented futher lubrication from reaching that area, As the bush wore, it allowed the mainshaft out of position, and gear shifting became progressiviely worse...

As always, your insight and experience with these machines is invaluable.

JDE

email (option): teladelujo@msn.com

Hi John..Yes it is usually the sleeve gear bushes that suffer first. The 'inboard' bush has three lubrication holes drilled through it from between the gear teeth. When installing new bushes press this one in first, drill down through the gear just enough to mark the outer surface of the bush and then press it out again and drill the three holes through.
You can drill these to say, 3/16"-1/4" diameter.
Then refit the bush to the gear along with the outer bush and finally bore/ream both buses to finished size. Clearance between the mainshaft and bushes should be .0015"-.0035" on completion.
The reason for fitting the inboard bush and then removing it to drill through is that the oil holes are at an angle to the bush and the small diameter drill needed to pass through the gear has a distinct inclination to snap as it breaks through the bush (at an angle)....Ian

email (option): ian@wright52.plus.com

Just a quick addage to the excellent information,sorted head gasket and running in my bike gently,rebuilt my box with new bushes and bike selects well on up changes,only problem is if i rush the fourth to third on slowing down it is unhappy,is this normal as it seems a steady select box,revs right and slowing into a corner down to third[yes i think most m20 men stay in top ]it selects ok but if i try rush it as the car infront stops to answer her phone [she`s only young bless!]its clunky,realy slow it selects ok but try rush it and its not happy.selection adjustment? or am i perhaps out of sink with a 72 year old box,unfortunatly came from a norton box.

Hi Arthur..The M20 box is basically a thirties hand change box with an enclosed mechanism to convert it to foot change.
Triumph boxes from about 1936 and post war 'camplate' operated boxes from BSA, Norton etc. represent the 'next generation' in gearbox design and are much 'quicker', having a mechanically simpler and more direct action with lighter gears and therefore less inertia.
The heavy gears and convoluted gear change mechanism of the M20 make it a slow box which works (reasonably) well if you give everything time to slow down or speed up as required. If you rush it you will find various false neutrals...Definitely a case of 'sit back and enjoy the scenery' ..As a 'P.S.' to my reply to John Edwards I made an error in my description..the oil holes in the sleeve gear are not located between the gear teeth but in the face of the gear...Ian

email (option): ian@wright52.plus.com

thanks Ian for advise,managed another 60 mile this morning and getting used to the box better,leaving things be,arthur.

Thanks for al THE good help! I've found THE problem...... It was à spring that was broken... Replaced THE spring and made à few adjustments and shifting gears is beter than before!

Thanks Thanks Thanks!

See u all on 6 june 2014 at normandy! I Will be at THE pegasus bridge drinking à Coffee and à beer With Ian! Made him à promise!!

email (option): bsam20@ziggo.nl

I'm looking forward to it Bjorn...nice of you to remember...(and make sure you have a spare gearchange spring in your toolkit!)..Ian

email (option): ian@wright52.plus.com