'69 TRIUMPH BONNEVILLE
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This is the story of a project which I began many years ago.
It was the middle of the 1970s and the Arab oil embargo was in full swing.
Gasoline prices were going thru the roof and, more significantly, octane ratings were plummeting.
With no one interested in hi-performance cars, getting rid of the lead in fuel faced
This hit my Triumph especially hard as the bike had been built to the ragged edge
during previous modifications.
Now with the falling octane, the bike was quickly becoming undriveable.
I was faced with the unpleasant alternative of giving up some of the power to which I had
become so addicted.
After wracking my brain for months
I finally hit upon the idea of building a water cooled head for the
bike. I reasoned that if I could get the temperature down then I could
live with the lower octane fuel. And so began the project of the liquid
cooled head for the Bonneville.
I had enrolled in night classes at the local vo-tech college for
a machine shop class about a year before. This gave me access to the
machine tools I would need.
The project began with a solid
block of 6061 T6 aluminum. My first step was to map out the location
of the head bolts. Using the old head as a
pattern I drilled the bolt holes with a Bridgeport (this is
a universal type milling machine). The next layout problem was the
location of and set-up for the combustion chambers. My instructor was
a shop foreman for Martin Merietta ( they build all that military stuff
that the government buys). I approached him about the problem and after
some research he found a tech article about cutting hemisphere segments.
After much dreaded math and some testing, the combustion chambers were finally cut.
The next problem was locating and cutting valve pockets.
the original head , the valve guides were located and from them the
valve seat locations. I had had some experience with hard seats in
the automotive industry so it was only logical that I use them in this
head. I made drivers for the seats and cut the heads for an interference fit. The wife was not amused when I told her I was going to need her
oven for the afternoon to "cook" my head. Setting the oven at 500
degrees I "soaked" the head for approximately an hour while "shrinking"
the seats and drivers in dry ice and acetone. Then, one seat at a time,
I would remove the head from the oven, drive a seat in place, and
return the head to "soak" again. I did this until all four seats were
The exhaust spigots
were made from 201 stainless and anchored securely to the head with socket head screws( no more loose exhaust spigots) .
While I did retain
the original phosphor bronze valve guides I secured them with a retainer/
valve spring seat which allowed the springs to bear on the shoulder of
the guide there by eliminating the possibility of a guide coming loose.
The project proceeded slowly by solving one problem
at a time. I laid out the intake ports to fit a DCOE 40 Weber carburetor.
This provided me with almost infinite tuneability.
Eventually I reached the point of installing the head and trying to get the
engine to run.
I fabricated mounts for two automotive heater cores and installed them
on both sides of the front down tube. Until this point I had hoped that the water
would circulate by means of thermal siphoning. Ha! What a joke. The water boiled
almost immediately proving wishful thinking is a poor substitute for planning.
So back to the drawing board I went. What I found was that water pumps were easy to
build, water pump seals were just about impossible to build. I tried to find a seal
from some other application which I could adapt but nothing presented itself. Well you
know what they say about necessity being the mother of invention. In desperation I hit upon
the idea of using motor oil in stead of water as a coolant. At first, this seems a rather
extreme solution for a problem with a water pump seal but once you stop and think about it
there are several good incidental benefits to this idea. First, the immediate problem is
solved. To seal the "coolant" at the "water" pump shaft I simply installed a sealed bearing
for the shaft. Since I was going to drive the pump from the alternator shaft, if the seal
were ever to leak the oil would only go to the primary case. I had removed the crank shaft
seal long ago allowing the primary case to be lubricated from the crankcase vent
a little more oil meant nothing.
The next advantage was that there would be no corrosion
ever. Third, oil had a high enough boiling point that the engine would over heat long before
"boil over" became a problem. Then I had another one of those inspirations which make projects really
neat. I thought, instead of using the oil tank on the right side of the frame as the
not use the head and cooling system as the reservoir. By plumbing the supply and return lines
into the back of the head I had plenty of oil for lubrication. I did not remove the oil
tank for appearance sake but did leave it dry.
While it is true that oil has only about
three fourths the specific heat of water, coolant for cars isn't actually water either.
Antifreeze has a lower specific heat than water as well. So it was only necessary to provide
a cooling system sufficiently large to over come the difference. Once that is accomplished,
another nice thing happens. I later found that, when I left my house to go to work in the
morning, by the time I got out of my subdivision the temperature was up to 150 degrees,
by the time I got to the four lane it had hit 180, and by the time I got to work I was
running at about 200. This was ideal for lubricating oil. The oil was heated almost immediately
but quickly stabilized at a high enough temperature to drive the moisture out. When I began
riding the bike on a daily basis I found that the temperature never got above about 240.
Perhaps a little high but this was only in the middle of summer when caught in traffic. I
never found it necessary to mount fans to maintain the temperature.
I rode this motorcycle from late 1978 to 1982. During that time it performed as expected.
It started well, thanks to the Hunt magneto and the Weber, and was very dependable. The only
problem that I had was the heater cores which I used as radiators. The Triumph shook and
vibrated so that I was constantly having to resolder the core tanks. Perhaps if I could
have come up with better cushioning for the mounts this might have been less of a problem.
As far as the fuel was concerned, even though the octane continued to fall during that time
period I did not have problems with spark knock except under the worst conditions.
All in all this project was definitely a success.
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