There are quite a few of these to work through.
Anyone reading my blog might ask why I have 6 gearboxes when I’m restoring 3 bikes. Well, I also have 2 early flat-tank Model K Velocettes to restore when I’ve finished the current 3 bikes and so I actually need 5 gearboxes in total ….I seem to have acquired a spare along the way.
Regarding clutches, some came with the various bikes but I also acquired a number of these in a job-lot many years ago from a guy that collected Sinclair C5s and had no need for Velocette parts.
So, which gearbox goes on which bike? To the best of my knowledge, they identify as follows:
#1 not sure where this came from…
#2 a later, desirable 4-speed ‘box
#3 one of the flat-tankers with a very early bolt-on shift mechanism
#4 KTT 305
#5 KTT 55
#6 one that I acquired as a spare
The factory records give the gearbox numbers for each bike – these numbers can be seen on this page of my blog for the KTTs but unfortunately the part of the gearbox on which the numbers were originally stamped is prone to damage and is either missing (#1) or has been repaired (#4 and #5).
As I will eventually need 5 gearboxes, I decided that I would check and rejuvenate all 6 – it seems pointless only doing 5 of them.
Before starting any project, it is always useful to do some background research and so I looked for what articles were available on these particular ‘boxes. Firstly, the Velocette workshop manual from the period: the section for “Dismantling The Gearbox” is reproduced below.
Secondly, “Norm’s Technicalities”
which contains a wealth of information, for example,
about detailed dimensions of clutch components and much more but not a great deal about these particular gearboxes. BTW, this booklet is only available to members of the Velocette Owners Club – one of many good reasons to join the club if you have a Velo.
And, last, but by no means least, articles in “Fishtail”, the VOCs magazine. The problem with this last option is knowing in which copy of Fishtail to look. This magazine comes through my letterbox every 2 months and have just passed Fishtail number 500. I have hard copies going back to 332 from when I joined the club in 2003 and have searched through these for any articles relating to Mk 1 OHC gearbox rebuilds but found very little. All the magazines are available online on the VOCs website and the index page is viewable back to #433 but searching the remainder would involve downloading them all ….and I simply don’t have time to do that.
Anyway, none of this is critical to rebuilding a gearbox and so, starting with gearbox #1, the first step is to dismantle the ‘box to assess the state of the internals and the castings. I have never taken apart one of these early OHC Velocette gearboxes but I have worked on plenty of other gearboxes in my life (from a D1 Bantam in the mid 1960s – you have to start somewhere – through Sturmey Archer CS, EIV, Dolls Head and later AMC to various Burmans, early Ariel, AJS and later Type 12 and 14 Velocette ‘boxes) to know what to expect.
A few points to note on stripping this gearbox:
The gearboxes that I am working on have not been apart for probably at least 50 years. Apart from the necessity of applying some heat to drop out the bearings I also found it necessary to apply heat to a couple of the bearings to free-off the shafts from the bearing inners on the end cover. Yes you did read that right – more below…..
The Kickstart Shaft End Cover (B-4/3)
has a LEFT-HAND THREAD (this one has had a hard past life that requires a bit of remedial work – see later - but otherwise quite serviceable). I have pin wrenches of various sizes but this was so gummed up that I ended up using 2x ¼” steel pins spaced the correct distance in the vice to lock into 2 of the holes, as shown in the above picture, and rotating the end cover. It will be reassembled with a pin wrench.
After stripping the gearbox, degreasing (I use cellulose thinners) and after a few hours in the tumbler (one of these with ceramic triangle media – it’s important to count the number of items going into and coming out of the tumbler to avoid mislaying small parts) the picture below shows the complete collection of the internals. Every ferrous part is given a hand massage with oil to stop them immediately going rusty.
Velocette produced different gear sets – both ratios and materials/heat treatment. The picture below shows the main and layshaft cluster from this gearbox
with the tooth count and part numbers. These are standard ratios and the “X” (which is stamped on each of the gears and the layshaft) indicates that they are oil-hardened rather than the earlier case-hardened version.
The gearbox shell and end-cover are vapour blasted to clean them up properly.
On this gearbox end cover, the mainshaft bearing simply fell out of the end – on the inside! The reason, which can be seen in the 2 pictures below, show the end cover from this gearbox, #1 on the right, to that of gearbox #4 (which is OK) on the left.
The part of the casting that retains the bearing has been completely broken off! Clearly, someone in the past has encountered the scenario described below and has hit the end of the mainshaft so hard that they have broken the casting and removed the inner part of the bearing housing. This is repairable – see later.
The reason for this is that the interference fit of the mainshaft (BK-5/3) into its bearing (B23) and the bearing surface on the end of the layshaft (BK-11X) into its bearing (B23/3) plus being nicely glued together with 50 year-old gummed-up oil makes it extremely difficult to get the shafts out of the bearings to be able to remove the end cover.
Now, back to my comment about applying heat - I use oxy-acetylene on these 2 bearings and although this will destroy the heat treatment of the bearings I prefer to renew the bearings than have to repair castings.
Bearings
There are a total of 4 bearings in the gearbox. In no particular order (OD x ID x t):
1) B23 (1 5/16” x ½” x 3/8”) mainshaft in the end cover
2) B22 (70mm x 35mm x 10mm) sleeve gear
3) B23/3 (1 7/8” x 7/8” x 3/8”) layshaft in end cover
4) B22/3 (1 9/16” x 5/8” x 7/16”) kickstart shaft in layshaft
The sleeve gear bearing is, as far as I am aware, only available from the Velo owners club. All of the others are standard off-the-shelf bearings. As I’ve mentioned in the past, I have been quite satisfied using bearings manufactured by KSK – they are a reasonably priced, made-in-Japan quality bearing however I have found a massive difference in price of these from different providers, for example, 24.37 GBP vs 7.80 GBP for B23/3 from 2 different suppliers for the same bearing – so, shop around!
Incidentally, there are cheaper “budget “no-name” bearings” around and I’m happy to use these for a lawnmower wheel bearing, but not in a Velo gearbox. If a manufacturer is not prepared to put their name to their product you have to question why you would buy it.
Anyway, back to the assessment:
There is a bit of rounding on the edges of the teeth on 2nd gear on both the layshaft and the mainshaft but, for anyone that has ever stripped a well-used AJS Big Port gearbox (which is of similar design in the respect that the layshaft has a fixed 2nd gear rather than a sliding gear), this one is like new! (There is a picture of the internals of the 3-speed AJS gearbox on my blog here for comparison).
One important difference between the contemporaneous Velocette and AJS gearboxes is that the Velo 'box has gear indexing inside the gearbox itself - parts B-64 and B-66/B-68 shown below
which gives positive selection of each gear, ie the precise location and holding-in-position of the sliding gear on the mainshaft. Gear indexing on the AJS gearbox, however, relies on the gate positions on the petrol tank hand-change, which I'm sure was fine when everything was new and had been properly set up at the factory, but not when the linkages - the trunnions and clevis pins - became worn and were set up incorrectly from rider maintenance.
One part that did need some attention was the Kickstart Shaft End Cover (B-4/3). This has had a hard life and although the L-H thread was good the tool(s) used to remove or retighten it in the past have resulted in small through-holes. In service, at least one of these will be below the oil level in the gearbox and, realizing this, somebody has tried soldering a couple of these.
I decided to re-solder these and the other 2 where the surface was paper thin.
The small amount of machining is to ensure that the solder does not contact the bearing inner.
However, in addition to the mainshaft bearing housing in the end cover that needed repairing, the gearbox shell had obviously had a harder life than the internals. I found the following issues to sort out:
2 of the ¼” BSW threads in the shell that hold on the end cover had stripped at some stage and been re-tapped to 5/16” BSW (top centre and top left in the picture below) and one of these oversize threads was not looking too good.
One of the threads for the main supporting studs had been tapped oversize and a new shouldered stud made to fit.
There was also damage to the case at the top right of the picture where the corner has been knocked off.
Last, but by no means least, the gearbox had probably been standing in a damp environment for many years and was deeply corroded on the underside.
I decided to leave the repair that resulted in the oversize shouldered fixing stud – I could fill and re-tap the hole to its original size – but the repair had been carried out competently and the new oversize thread in the casing was good. But I did fill (using lumiweld) and re-tap back to ¼” BSW the threaded holes in the front of the casing
with the help of a bracket from the positive stop to ensure the holes were in the right place
and I also repaired the chipped corner on the top but the corroded part on the bottom proved a greater challenge. As soon as some heat was applied to this region this happened.
Parts of the corroded section were much thinner that I had anticipated and any further attempts at repairing this using heat would be futile. I therefore decided to use Devcon Aluminium Epoxy which, although would not be as strong as a welded repair, would be sufficiently robust to withstand the oil, heat and vibration that would be experienced in use and there is still plenty of material to provide structural rigidity to the shell.
I reinforced the Devcon layer using a piece of brass gauze
and after 2 applications ended up with this.
After sanding back, repair to the shell is complete.
To repair the mainshaft bearing housing in the end cover, the casting was set up on-centre on the rotary table on the milling machine
and then offsetting in the X direction and using an end mill to clean up the surface
ready to accept an annular disc, made from 6082 aluminium,
that is currently at EMP tooling to laser weld the disc to the cover.
I have also stripped gearboxes #4 and #5 from both KTTs.
to assess what repairs these might need and to order bearings – it’s just easier to order them all at once rather than separately. So, I’m now waiting for the laser welding to be completed, bearings to arrive in the post and the last castings to come back from vapour blasting …..more next time.
Controls and Cables
While waiting for external things to happen I’ve been sorting out controls – levers and cables. This is not usually the stage of a project when I’m dealing with controls – it’s one of the last things at the end of the dry build, however, the supplier, Carrot Cycles, that has been providing all my cable-making bits and pieces for many years plans to retire at the end of the year. I have always found them reliable with exactly the correct sizes of inners/outers/ferrules/adjusters etc. and at fair prices so I decided to order cabling components for all my upcoming projects - these 3 Velos + 2x flat-tank cammy Velos + 2x AJS Big Ports – 7 bikes in total.
It took some time to work out exactly how much of each item I would need and my best estimate has just seen delivery of this lot.
I’ve also been sorting out some of the controls – here are the 6 Air and Ignition levers that I will need for the 3 bikes of this project.
And Finally……
I was out on the AJS 33/7 recently – the last bike I restored – and my good buddy JT said that I look like I’m riding a Bantam (most bikes of that era are pretty small compared to today’s bikes). Now, anyone that knows old British bikes will know that a BSA Bantam was not exactly a superbike of the day – it was a small ride-to-work mount (with apologies to the Bantam Racing Club…).
Having now completed the saddles for the 3 Velos that I’m working on
I thought I’d better try these bikes for size. For a tall person (I used to be 6’ 5” when I was younger) all I can say is that these are pretty small bikes!
I’m not going to post a picture of me sitting on one of these but, by chance, I do have a picture of me astride a D14/4 Bantam.
This picture is from nearly 50 years ago – I believe it is 1977 outside a house in Winchmore Hill, North London that my then-girlfriend (later, and still, my wife) and I had just purchased. She took the picture.
You might wonder why I have a hosepipe wrapped around my waist… Well, at the time I was about halfway through my PhD at Imperial College, sharing a small office with 4 other guys and commuting every day across London between my home and Exhibition Road in South Kensington – a lovely ride through Regents Park and Hyde Park of about 14 miles. One day, they decided to renew all the internal fire hoses at the college (there was nothing obvious wrong with them but they did this every few years) and I needed a hosepipe for the garden. So, I acquired a free hosepipe, but how to get it home? The answer’s in the picture – my Michelin Man impression. But it worked!
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