Gearbox adjustment Pre unit

[MGI]

Having removed the tank & saddle to facilitate simple access to allow removal & replacement of the dynamo, and to check the routing of the throttle cable, I thought I would check the primary chain tension whilst awaiting the delivery of the said new dynamo. To my surprise I discovered it was as rigid as an iron bar. So having ascertained that the adjustment bolts were 25/32 AF and having acquired necessary sockets and spanners I set about the task. Page 123 of 'The book of the BSA' by W.C.Haycroft informed me that it was necessary to loosen bolts A & B, A being a bolt underneath the gearbox (SA models 54-59) and B the bolt in plain view above the gearbox. The immediate problem was the conspicous absence of bolt A. I never did find it, and soldiered on regardless, not forgetting to adjust the secondary chain to compensate. I know my machine is a mongrel with a multitude of donor parts but the frame is unquestionably a 58 model and so I am completely baffled by the fact that I appear to possess a gearbox which is secured and adjusted at the top only!

[DAVE BRADY]

Good evening,

It may be worth, if you haven't already, actually looking under the bike to see if there is a hole for this bolt?  This bolt is vital as the gearbox pivots on this bolt with the top one being in a slot to allow the pivoting for adjustment.  If there is no bottom bolt then when you adjust the rear chain it will pull gearbox back, pivoting on the top bolt and in effect tighten the primary chain.
Did you re-check the primary after adjusting the rear?  Even if it has not gone tight during adjustment the next time you ride the bike    it will as you put power through the transmission.

Dave.

[MGI]

OK, thanks Dave... it is still on the ramp, I will examine it tomorrow (more thoroughly).

[MGI]

Panic over, the location of the bottom bolt has been established... Firstly it appears to be further back than the book of the BSA implies (Ditto The book of the BSA [B & M]) and secondly it is concealed by the starter motor! All is well that ends well!

[morven21]

The starter motor? !   

[MGI]

Yes, starter motor... I have a really painful slipped miniscus in my right knee (Cartilage?) I have had it for two years, the Vet assured me it would improve but this has not turned out to be the case, bullet bit, readies drastically reduced, but sublimely easy starting! Ideal! Just need to sort out the centre stand now!

[B Murphy]

Is it the Phil Pearson electric start version? I would like an electric start but I think they only work from a 12v battery? My B31 is still 6v.

[idie]

When you buy the electric start kit, which I have fitted to my B33 three years ago. You will get every thing for fitting. A 12 volt battery a regulator to change from 6 to 12 volt all the replacement bulbs. A new heavy duty rear chaincase. A double sprocket and chains for the starter. A starter motor and mounting plates. Allow a day to do. The only problem is the gearing will be high as the kit is meant for a GoldStar which has a greater output. The smallest sprocket is 21 tooth. The only way round it is to drop the size of the gearbox sprocket. That unfortunately brings with it another problem as the speedo is driven from the gearbox layshaft. This will turn faster so making the speedo operate faster. Might stop you getting a ticket. I had my speedo re-calibrated.

[B Murphy]

idie - is yours a Phil Pearson kit.

[idie]

Yes! Not cheap but the best thing that I have ever bought. My right knee loves it.

[MGI]

Yes, it is a Phil Pearson kit and it works well  the kit costs about £2000 installed and if you get there early it might be finished in a day. In addition I had to purchase a splined spacer gizmo because my engine is XB being 1947 which had a four cam cush drive whereas the kit only works with a two cam cush drive. As Idie comments, they install all that is required to convert the system to 12 volts even though the dynamo remains 6 volts which works, the dynamo needs to be converted to negative earth though. Since getting my bike back I have purchased a later dynamo (Longer than my original) which has been converted to 12 Volts by Kidderminster Motorcycles, who are only a few miles from me. It gives a full charge following the starting procedure and then gradually drops to nothing which is as it should be. The Gizmo cost £125 plus postage from George  Prew (who, like Kidderminster Motorcycles, advertises regularly in the BSAOC mag)

[DAVE BRADY]

Good morning,

I have posted this info. in another thread but I thought it might be useful here as well re centre stand.
Check out The Star for April 2017. An interesting article re lever assistance for centre stand.

Dave.

[MGI]

Ideal!

[B Murphy]

If anyone has the article would be good to upload it if possible please.

[JulianS]

back issues of The Star magazine are available in the mebers area of the BSAOC website.