The powder coating and chrome plating came back from their
respective suppliers towards the end of January and work started on reassembly.
However, I didn’t get far before my wife and I set off on a trip to Kenya that had
been planned way back in 2022.
The trip involved safaris in 3 different national parks (Masai
Mara, Lake Nakura and Amboseli, adjacent to Mt Kilimanjaro) and we spent quite
a bit of time travelling by road between these. It is always interesting to observe
motorcycling in different countries around the world; in most of Europe, the
US and the Antipodes motorcycling is predominantly for pleasure and more often on large capacity
bikes whereas, for example, in India or Kenya motorcycles are mostly smaller
capacity “workhorses” and are used for transporting the family or goods around.
Any visitor travelling on Indian roads will regularly come across a family of 5
astride a small TVS motorcycle.
I came across 3 interesting uses of motorcycle workhorses in
Kenya. The first had a very substantial sheet metal folder strapped across the
back seat, the second boasted a large 3-seater sofa across the back (I’m not
sure whether the sofa was being transported or this was an up-market taxi
service) and the third, and by the far the most impressive, was this one.
It is not so easy to see the bike under the Makuti thatching
– the dried leaves of the coconut. As we drew alongside the rider is visible
and who just about manages a smile although the guy perched precariously
on top doesn’t seem too happy
Looking through a few old pictures recently I also stumbled across this one from a trip to Vietnam.
Before setting off for Kenya, I had managed to start
reassembly of the bike.
The engine bottom-end was assembled and, together with the
gearbox, was inserted into the frame.
The stem for the girder forks has also been attached with new 3/16” balls in
the bearing cups.
The inner timing case is fixed and 3x 3/16” studs have been
screwed into 3 of the 3/16” BSW threaded holes that support the cassette/bearing
housing for the camshaft and magneto drive. The inner part of the cassette is a
tight fit in the timing case housing and rather than trying to twist it into
position later (and the same with the outer part of the cassette) it is much
easier to use these studs to position it correctly on first assembly.
The bottom pivot for the cam chain blade tensioner has zero space on which to get a spanner or a socket and I tighten this using a
machine chuck that is usually found in the lathe tailstock.
It is not possible to screw in the tension blade pivot and then insert the inner part of the cassette because part of the thread for the blade pivot is contained in the cassette itself.
Before completing this part of the assembly, the 20-tooth crankshaft pinion was mounted onto the keyed crankshaft.
The outer part of the cassette could now be assembled.
and all screws lock-wired.
It was now time to set up the valve timing. The 1933 OHC manual
gives the following diagram for valve and ignition timing:
From this, I would discern the following:
IVO 200 BTDC
IVC 550 ABDC
EVO 680 BBDC
EVC 250 ATDC
Ignition: 500 BTDC fully advanced
Although both the inlet and exhaust periods are relatively
short by modern standards, they are not unreasonable and in any case, I only
have one camshaft and the only aspect that I can change is the phasing of the
entire cam events.
I set a 0.010” tappet clearance and set crankshaft and
camshaft at EVO (crankshaft with a degree marker disc and camshaft vernier
adjuster position determined when clearance went to zero) to see what the other
timing events would be. This gave measurements of:
IVO 190 BTDC
IVC 600 ABDC
EVO 680 BBDC
EVC 320 ATDC
These are remarkable close to those given in the manual and
I decided to stay with this setting.
However, 500 BTDC for ignition timing is far too
advanced by modern standards. One has to be careful in interpreting certain information
given in manuals of the period and this applies to ignition timing. Why? Well,
because fuels used in the 1920s and 1930s had quite different characteristics compared
to fuels of today and the optimum engine settings were selected for the fuel
that was available at the time.
The following graph gives a lot of insight into the
evolution of fuels from the 1920s.
ref: A Historical Analysis of the
Co-evolution of Gasoline Octane Number and Spark-Ignition Engines, Splitter,D.,
Pawloski, A. and Wagner, R. Front. Mech. Eng., 06 January 2016 Sec. Engine and Automotive Engineering
Although this graph is based on data from the US, the trends
in Europe would have been similar. There are a number of points of interest
that can be gleaned from this graph. Firstly, the red line shows that the fuel
AKI (Anti Knock Index) or octane number increases steadily from a value of around 62 in the late 1920s to 90 in 1970 with a particularly steep increase in the
1930s and 1940s. This is extremely important in determining the maximum useable
compression ratio and which, in turn, correspondingly increases from 4.5 to 9
over a 30-year period. (note: the US uses AKI = (RON + MON)/2 – the average
of two different methods of measuring the octane number whereas Europe uses
RON. RON is higher than MON. Nevertheless, the conclusions would be the same).
The purpose of this brief excursion into the evolution of
fuel characteristics is to illustrate how this contributed to rapid engine
development that occurred during the early days of the internal combustion
engine …..and why 500 BTDC for ignition timing would have been OK in
1933 but not today.
I decided to set the timing at 380 BTDC fully
advanced. With a compression ratio of 9:1 the engine may knock under low speed,
high load conditions but with 30 degrees of manual retard available a good
setting will be found and adjustments made if required.
2 new stand springs (I only had one) were made by Alberta Springs
and it took just a couple of days to get something that looked
like a reassembled motorcycle.
The oil tank was rubbed down by hand and sprayed with 2k
etch primer and 2 coats of gloss black. As I’ve probably mentioned before, I never
send oil tanks out to be powder coated because of the risk of grit
remaining in crevices inside the tank in spite of ones best efforts to mask every entry point prior to grit blasting and flush out every grit molecule when finished.
There are obviously a few more bits to bolt on and there is
still a bit of work needed to finish the petrol tank – painting, gold leaf
lining and the “AJS” insignia but the bike is now nearing completion.