Clutch hub adaptor disaster

[alanp]

I'd like to forewarn about a problem I've just had.
I was going to remove the clutch from my A10 and had got to the stage of pulling the clutch hub adaptor off the gearbox mainshaft taper with the extractor and it just wouldn't budge. This has never been a problem before and didn't make sense. After numerous attempts the thread on the extractor had been stretched and had lost its grip on the hub adaptor internal thread.
I eventually removed the hub adaptor by welding the extractor to the hub adaptor. Desperate measure eh?
Analysing the hub adaptor, key and shaft keyway revealed the reason - the 0.20" key was a slightly loose fit in the shaft keyway but was loose in the 1/4" key slot in the hub adaptor! The side of the keyway in the shaft had chipped and the key tilted to push the chip to jam the chip between the shaft and the hub adaptor, hence the amount of effort needed to withdraw the hub adaptor from the shaft.
The shaft is now unusable and the hub adaptor and extractor are both destroyed.
When I get to rebuild this area I will need to ensure that the key is a good fit in both the shaft and the hub adaptor, which may not be the same width. You can't rely on the taper fit to carry drive torque without any side load on the key, hence the usual chipped keyways you see on BSA boxes.
Judging by what I hear about the variations of the tapers in the hub adaptors available I'm not looking forward to this.

[chaterlea25]

Hi Alan,
Thats a bummer!!!!
I always lap the adaptor onto the mainshaft with some fine grinding paste a quick rub will show the contact area
if the  hub taper is way off I machine it, using a spare mainshaft and a 0.0001 dial gauge to set the compound slide on the lathe to match the taper.
Contrary to commonly held beliefs its the taper that takes the load, a proper fittong taper is almost as good as a solid piece of steel
Its badly fitting tapers and the centre nut not tightened properly that damages the mainshafts
Get or make a clutch holding tool so as you can hold the clutch from rotating
Ditch the dopey lockwasher and use some threadlocker on properly cleaned threads
Tighten the nut to 65ftlbs

HTH
John O R

[A10Boy]

I fully agree with John.

Its usually a loose centre nut that results in a destroyed keyway. The key isnt intended to carry load, the load is carried by the taper. [As in some villiers engines which dont have a taper on their flywheels]. Therefore, a chipped keyway is still servicable as long as the centre is a good fit on the taper and the nut is tight enough. Theres no need to change the shaft until the next gearbox re-build if at all. As John says, 65 FtLbs is right and the only way to hold the drum to tighten it to that torque is by using a holding tool. Also, you can easily check the "fit" of the center on the taper with a small dab of engineers blue [available from ebay!].

Ive had the extractor pull out of the clutch center before, just grind or lathe off the damaged thread area from the extractor and drill or lathe the internal deeper so it reaches the threads again and it will be ok.

When you buy a replacement clutch center / adaptor, beware there are two manufacturing faults I have discovered.

1, On some of them, the roller bearing face isnt machined to the right depth so when you fit the [correct] rollers and the cast iron centre it all binds up. [although these may have all gone from circulation by now]. You can check this by doing a quick trial fit on the bench.

2, The spiral external oil throw is machined the wrong hand so it throw oil OUT of the back of the clutch, not back into the chaincase.

I have found both of these in my travels, I have a canal at the bottom of my garden, guess where they are now...

Regards

Andy

[alanp]

Just checked two other hub adaptors for fit on the shaft taper. One seems fine, the other wobbles around like a big wobbly thing. Don't you just love this hobby of ours?
Andy, I went through that repair sequence on the extractor at the time and 'she' was jammed fast and knackered the repaired thread as well.
Alan

[roadrocket.chris]

an old engineering trick is to put chalk powder on the taper it stops them slipping it does work.

[brackenfel]

Hi Alan,
I've just found this post doing a quick search for "clutch nut" so it's saved me reinventing the wheel by asking a similar question!  Thanks! I've reached the stage where I'm tightening up the centre nut (4 spring clutch)..

Have had all sorts of grief with what should be a straightforward job as I swapped to a slightly better mainshaft only to find the key didn't fit. Spent ages filing & then ordered another from C&D Autos... This proved that the original one I had was too long but that the new one was too tall for the newer shaft. So , rather than ruin the new key I shortened the old one and am now nervously putting it
all back together. This has shown me that keyways differ in length and, I suspect, depth!

On top of this the nut would not go along the thread on the replacement shaft beyond the point where the back of the nut was flush with the end of the shaft so the lockwasher & spacer simply wobbled about! I cured this by running the nut up the thread on the old shaft held in a vice with a socket & bar until a bit of swarf came off the back of the nut!!

As you can imagine none of this inspired confidence!! Anyway, I'm now going to see how close I can get to the 65lbs recommended by John using 4th gear & brake pedal and hope for the best!! I've reached the "brute force & ignorance" phase now as this bl**dy bike has been off the road almost the entire time I've owned it!!

As Alan says "Don't you just love this hobby of ours?"

Cheers,

Adrian

[bsa-bill]

Adrain - please take the time to make a clutch locking tool or wait and buy one.
I have used the stand on the back brake pedal a few times with success and the last time with regret and a leg still tender three months later,, the (NEW) brake cable snapped, my leg went from stationary to hypersonic at a rate to be proud of at Santa Pod, the bruising is almost gone now but still some pain.
Needless to say the cable went back to the supplier, I didn't pursue damages ( I thought if the judge is a motorcyclist he might ask how I managed to use my right leg for braking on an old Brit bike)

The force needed to hold the rear wheel fast with the brake has to be on some sort of logarithmic scale to the 65 lb/ft at the clutch centre

Don't do it, legs are handy (in pairs)

[wilko]

A rattle gun will do the job with loktite!

[brackenfel]

Hi Bill,
Thanks for the warning - hope the leg mends ok.. 

My brake cable is still an older original type - the shiny new replacement I bought has an outer that is too long - haven't bothered to return it to the (Ebay) supplier...
I'll see if a mate has any plain plates (I have spares of the bonded ones) to lash something up..  I was originally able to undo the thing without too much fuss or any special tools so perhaps 65lb ft is more than needed??  I'll get the trusty torque wrench out & see how much I can apply without putting myself at risk... I expect I'll need the holding tool in the end though..

Thanks again,

Adrian

[brackenfel]

Hi Alan, Bill & John,
Am still on this one but making progress.. Have so far applied between 50 & 55 Lbft to the nut and am thinking this is probably as far as I want to go as I've had to be a bit rough with the nut in the past & threads may not be "as new"... Am I right or should I risk another 10lbs??

I've also got it so that the nut lines up nicely with the tabs on the washer (see pic).. I may give it a little more just to line up perfectly but don't want to break anyhing at this stage... I guess the split is for if the nut ends up part way betwen 2 flats..

I didn't ignore warnings about special tools but my mate is away & patience is not one of my strong points so I improvised a little & came up with another way of locking things up..
As I have a nice new AM26 on the back I thought I'd test it's grip potential!!
4th gear selected, "T" shaped piece of wood inserted under it while turning the wheel to grip it. ( the peice of wood was hanging around from evening class in woodwork years ago). The "T" shape stops it turning.
A bit of rear brake applied for insurance & lean on the torque wrench ....   Totally at your own risk but it has worked for me, thought others might find it useful.. Obviously to undo  - place wooden "T" at the other end of the tyre...

Cheers,
Adrian

[bsa-bill]

Nice one  - necessity being the mother of invention once more

For anyone interested there is a four spring clutch on Ebay item 190460536455 at £127
 with just over an hour to go, last bid was about half three

[chaterlea25]

Hi Adrian,
Sorry to be the bearer of bad news?????
I hope you took the pic as a mock up???
You forgot the clutch pins which have to be put in from the back of the centre before fitting
Maybe you have discovered this since you posted???

Regards
John O R

[brackenfel]

Hi John,
Oh b*gg*r.....
Just when I was feeling please with myself.... Not a mock-up I'm afraid, a proper cock-up...  I spent so much time worrying about the woodruf key & the centre nut that I forgot them..

Now I expect that it won't come off again.....

Thanks for that - appreciated. I would have found out later today when I got to the next stage.......

Cheers,

Adrian