has been a good while since this was updated, as Richard, who always
did the website work, has been engaged in other business. I am
finally trying to get to grips with this and hope that you will
forgive the “Rough Edges”
let me review the progress with the Scott racer over the last three
feedback from Paul Dobbs had been that there was not enough weight
over the front wheel.
was necessary to lift the seat higher than the long tank and move it
forwards over the tank to try the revised weight distribution. Paul
had pronounced the handling transformed and had considerable racing
success with this layout.
It was, however, untidy and so I had the
tank shortened, so I could have the seat in the same position but
lower behind the tank. The seat mountings were modified to suit the
new seat position. Unfortunately, the exhaust system would not now
pass the revised seat mountings and so it had to be modified with a
big hammer! It was not beautiful, as I am no expert with sheet
metal. The result was that the power was down from 35 to about 33
bhp and the handling had deteriorated again.
original cylinder head was not of my original manufacture and was not
from high strength aluminium. It had been welded and machined
several times, so the decision was made to replace it with one of my
high compression heads. To go with this, a new pipe was made by
“Spec” a local specialist. He looked at my previous efforts
without comment, but I could see his lip curl.
path of the developer is strewn with difficulties and when more metal
was eroded from my aluminium barrel in removing the existing chrome
plating, the bore was left oversize. Silk pistons were now not big
enough, so I made some 660cc pistons from old castings I had from
1977 in LM14 “Y” Alloy. All initially seemed OK, but then I was
troubled by a water leak into the LH crankcase.
barrel was an early casting and the four holding down bolts had gone
through to water. I had fitted stainless blind inserts, but the
recent plating erosion had exposed the threads of the insert in the
side wall of the exhaust port. Water was leaking in by this route.
What to do? I had put a lot of work into this barrel and do not have
time to make another one as I must attend to the engines of my
customers. I decided to try and seal the leak by pouring some slow
set epoxy into the water space of the barrel near the exhaust port.
In this state I took the bike to be tested on the Heenan and Froude
dyno of Dave Holmes. To my great surprise, it recorded 41.9 bhp
which was a big increase in power.
bike was entered in the VMCC races on June 22nd at Mallory Park with
Paul Dobbs as rider. Paul reported that the handling had not
improved and that the engine had tightened, but had become free
Soon after this meeting, and without time to strip and check the motor, We journeyed to make our attempt at the speed run for the fastest Scott record down at Woodbridge airfield in Suffolk. We had the big dustbin fairing fitted for the occasion, and moved the seat position to enable Richard to really get down behind it. Preparations for this event were assisted by Daiji, A meticulous and spirited Japanese man who had been working with us for the previous couple of weeks as part of a British tour of vintage and classic motorcycle engineering workshops. It was obvious from the beginning that it was difficult to start, but we put this mostly down to the tall gearing and maybe attributed a little to the possibility that the new exhaust was causing a pulse in the inlet tract which was affecting the charge flow at starting revs. A possibility brought to our attention by another Vintage racer who had himself suffered it. Though these both might have been factors, the lions share of the problem was likely caused partly because, as later we realised, by at least one partially stuck in ring.
Richard made a sighting run, but sensed that it might have partially tightened even during this. Events were taken beyond our control however when extreme cross winds got up and we were advised against any further high speed runs. Richard did some quarter mile runs on his Scott, so we still had a good weekend.
The next day, the
engine was stripped and it was found that in the areas near to where
the epoxy had been cast into the barrel water space, this had
hindered cooling and had likely contributed to seizures on both pistons. Both
rings were stuck in their grooves.
No wonder it was hard to start!
pistons were reground on the outside diameter and the piston crowns
remachined to drop the compression a little. As regards the
handling, I wondered if the height of the seat was significant, so I
raised it about 15mm. It was in this condition and without much
confidence, that Richard and I went to the Beezumph track event at
Cadwell Park. I suppose that if you keep fighting against adversity,
you might be allowed a little success and indeed we had it, as the bike went better than
it had ever gone, both as regards power and handling!
Top speed is
estimated at approx 115mph naked with a definite boost from the exhaust.
The handling was much improved with the higher seat position and I
found myself going into corners at speeds that I could not safely do
I am 67 now and want to have some racing while I am able.
Over my 38 years of racing, I have fallen off many times, but in past
times, without significant damage to myself. The last two occasions
, however, I broke several bones and I am wondering if the bones are
getting softer or I have just forgotten how to crash safely. I am
loaded to go to Lydden tomorrow and am resolved to be restrained
until I feel truly confident. Life is a short and precious gift and
to go through it without any risks must be very boring. Racing,
especially Scotts, has brought many moments of pure ecstasy to my
life. If I had my time again, I would change nothing!
the work front
evidence of poorly assembled crank assemblies.
Scott owner from Australia, Kelvin Mears, is rebuilding a Scott and
sent me his cranks and rods to refurbish. In looking over the
cranks, I saw a strange pattern on the LH main bearing ring. It has
to be accepted, that although the main bearing design may look light,
they very rarely give trouble.
this case there was a bright line down the middle with a darker band
each side. Closer examination showed that the crank had been loose
in the flywheel and had been rocking about in use for so long, that
it had worn the main bearing ring into an arched profile. Next we
looked at the tapers of the cranks, and here was clear evidence of
fretting and even some metal transfer from the flywheel. I sent a
message to Kelvin to check out the flywheel and back came the reply
“It is ruined, what can you do”? I replied that I could supply a
new centre section that could be fitted into his flywheel after the
old centre was bored out. I think I had better make a small batch as
it is much cheaper to make others once you have a setup. I should
explain that Kelvin had not sent his complete engine due to the high
cost of freight from Australia, although I much prefer to have the
whole engine. From the UK, this week, came another enquiry. Can I
have a look at an engine as it vibrates. I suggested that the owner
checked the security of the engine and undertray in the frame. He
responded that this was all secure, so what else could he check?
Check the truth of the flywheel, I replied. It should run within
0.003” on the periphery and about 0.005” on the side of the rim.
little later came the reply that the periphery was running out 0.010”
and the side of the rim had a massive 0.040” wobble. Sounds like
another tapered flywheel insert is needed. It seems such a shame
that so often tapers are destroyed just through lack of correct
assembly. Remember, after you tighten the centre bolt, the cranks
MUST be knocked up (See assembly section on website)
cranks will travel a further 0.010” in this process. If you just
tighten the centre bolt only, the cranks will be loose within 10
my contention, that there is a fault in the design of the Scott crank
that has gone back to the earliest times. I maintain that the keyway
should be at right angles to the crankpin, not in line with it.
the “in line” position, at the point of maximum load when the
piston is near TDC, the loading is taken by that area of taper that
has at least 50% of it’s load bearing surface missing, by virtue of
make another crank run in the future, as the remaining stock is
dwindling, it might be better to make the cranks with the keyways
rotated 90 degrees. Talking to Richard, he suggested we could also
make a 360 degree motor to have a fashionable “Big Bang” engine,
or we could do a 270 degree crank so it sounded like a vee twin
Ducati. I told him that I was hardly tolerated now by some purists
and that such talk could have me thrown from the club. What else?
Well I finally sent John Hughes consignment in nice boxes to San
Diego. I wrote about this for Graham Parker to consider for
inclusion in our Newsletter, so you can read it there and if you are
not receiving the newsletter, then Why Not? It is free and we do it
for you not profit! If you are not on the distribution list, just
drop me a request at firstname.lastname@example.org
I had an enquiry for a complete new engine, but I explained that a
bespoke Moss replica engine from new high strength castings would be
expensive. I asked how the bike would be used and was told, as a
brisk road bike. I suggested an engine using a new, old stock,
Holder crankcase with reground main bearing cups, an iron barrel
bored for Silk pistons, a High Comp head and new high strength
cranks, new flywheel etc. With some gas flowing, this would make a
good engine at about 50% of the cost of a “One Off” all alloy
competition type motor. An order was placed and we are starting to
get components gathered together. In order to proceed with several
earlier jobs, I am involved in reconditioning about 30 con rods as a
batch. It is completely uneconomic to do them individually, due to
the considerable time spent setting up the machines for the different
will leave this here and when I return from Lydden, I will add a few
lines and pics about that.