After visiting the 2007 Hamm Diesel Motorcycle Rally earlier this
year I have been debating whether or not to write it up. I have finally
put pen to paper and the result may seem negative to some but please
do not take that view. I see the current diesel bikes as being something
like the scene with British bikes in the late fifties. They are about
to make some significant improvements. Despite what many will tell
you about stagnant development, most British bikes went to unit construction
and AC electrics during that time.
It was my first visit to the Hamm rally this year and I met up with
Stuart and Jeff after they had disembarked from the ferry at Dieppe.
From there we made our way across country to Mons. I had not seen
a diesel bike in the flesh before and was surprised how agile Stuart’s
bike was up to 45 mph. It also cruised happily at 50 to 60mph when
up to speed. The only time the diesel was at a real disadvantage was
when on the German autobahn; mainly because their lorry’s are
not allowed to over take and from time to time we were slower than
them.
At the show I spent my time looking at the various models, some such
as the Sommer production bikes, and others home brewed. They can be
broken into two camps, those using Enfield as a base bike and those
not. The Enfield we have now is essentially the 1955 model 350 or
500 base machine. The engine fits snugly into this frame. It is of
significance that the Redditch factory strengthened the frame in the
early 1960’s when they fitted the more powerful parallel twin
engines.
The Indian made diesel variant had a motor that was virtually the
same dimension as the original single cylinder motor, consequently
it was a good fit to the frame. Most of the other conversions I saw
cut away significant parts of the front down tube in order to accommodate
a bigger engine. I believe this weakens the frame, especially around
the area of the steering head. Given that the frame is already near
its limits I think this is a bad idea. Many had an alternative assembly,
most with the join being held together with two bolts which looked
to me as more likely to pivot than provide support for the steering
head. What I think would be better would be to cut the backbone tubes
and weld in a small extension and at the same time beef up the backbone
and steering head. This would give all the space needed, and improve
rather than weaken the frame. This would be especially useful to those
using the Hatz IB40, as then you could make room for the five speed
box.
Almost
all the engines used were industrial engines designed to run at a
fixed 3000 or 3600 rpm, in order to run generating sets. These speeds
coincide with European 50 Hz electrical supplies (3000) and American
60HZ at 3600rpm. Because of this the fuel injection system is statically
timed for peak efficiency at those rpms. Unfortunately this is too
far advanced for quiet idling and any low rev power. This makes the
power band very narrow. Sadly the Enfield four speed gearbox has a
wide change of ratios between third and top, which means the engine
drops to the bottom or below the power band when changing from third
to top; the five speed box avoids this. This is why I advocate using
it.
The
other problem which needs to be fixed is the timing. Somehow we will
have to get variable timing, if only a two position, slow speed and
fast speed setting. Having looked at a few pumps, I have not yet thought
of a solution to this problem. I had hoped they were like tractor
and older car pumps, mounted radially so could be manually controlled
by a handlebar mounted control lever like the old fashioned manual
advance and retard of fifties bikes.
I
think that for myself, I would want a bike with these attributes plus
enough power to cruise at 70-75. I did not see the bike for me at
the show, but many showed promise. I
think the ideal diesel bike will have three cylinders. This for balance
and vibration reasons. The same applies to petrol engined bikes.
If
you look back to cars, I can remember some fitted with commercial
diesel engines back in the fifties and sixties. They were cheap to
run but no fun to drive. Diesel engined cars did not catch on until
Peugeot made better, quieter engines. I think diesel bikes will not
catch on in a big way until they too are much more refined. This is
what we have to do and I hope I have pointed in the right direction.
I
have half a mind to get an Electra with a view to converting it some
years down the line when maybe the need will be greater and availability
of suitable engines better.
If
you compare a new Enfield Electra against a Sommer diesel. With a
couple of extras, better seat and bigger tank, the Electra would come
in at £4000, and the Sommer at about £5000. Assuming the
Electra does 80mpg and the Sommer 160 mpg it would take 32,000 miles
to break even (approximately), three to five years for me. This is
fair enough, except I think the Electra would be nicer to ride (very
subjective I know) This is because the Electra could match all the
slow speed attributes of a Sommer, but also manage faster bits of
motorway much better. I.e. it could hold 75mph maybe not where the
Electra is happiest, but certainly double, not so for the Sommer.
I
really think instead of chopping the frame to fit an engine, we need
to build a motor to fit the frame.
Larry
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