Time flies when you’re having fun, as they say. I certainly did not anticipate taking so long
to get back to relating the saga of prepping the replica of the 1987 version of
The Beast for last 4th of July’s Humboldt race. When I left off (with a race report
intervening) I had filled in some of the details on the frame and crankcase
modifications. At that point there was
no more time to write as all my time was taken up with finishing the bike in
time. So, back to the build …
Due to my inherent streak of being a cheapskate, I did not
order the flywheels from Truett and Osborn when I should have. Yes, sticker shock. It turns out that the 5-1/4” stroke I wanted,
made them a special order adding to the cost of the quite reasonable price of their
normal 5" wheels. Now, I could have just
gone ahead and built the motor with 5-inch wheels as a 114 inch, like the
original, but my drag racing philosophy has always boiled down to building as
big a motor as practical and put it in as light a chassis as practical. Besides, my preliminary calculations with rod
length, cylinder length, and the compression height of the pistons that I had on hand
showed that the 5-1/4 wheels would put me where I wanted to be for piston deck
height. Once I finally decided to bite the bullet and place the order, it was
nearly too late given the normal delays that happen in manufacturing. But T&O came through and I had the
flywheels in my hands with about 30 days left to finish the motor.
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| They really were in the mail! |
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Just what the doctor ordered
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Did I say, “finish the motor”? Sounds easy, doesn’t it? Truth is there are a lot of items on the
motor build that depend on the flywheels.
For instance, I needed an initial mock up to see how much the flywheel
diameter would need to be reduced in order to clear everything. As it turned out, the wrist pin ends of the
stock length Evo rods that I intended to use would not clear the wheels at
bottom dead center, which was not a surprise. That required reducing the
flywheel diameter by .420”, which in turn, required building up the flywheel
scraper in the crankcase to compensate. With that done I could finally add an
oil shedding coating to the flywheel and gearcase compartments. But with those details attended to, there was
still much to do. Once the crank could
be mocked up to rotate in the crankcases, there was still the matter of insuring
that the pistons would work with the heads before they could be weighed in
order to balance the flywheels. That
turned out to be just as difficult as I had foreseen. The domed pistons that I had on hand were a
used set from a previous drag motor, probably from the latter half of the
1980’s.
I had two sets of heads to choose from. One set was actually from the original 1987
version of the Beast and the other from my last attempt at a serious drag bike
which was nicknamed the White Knuckle Express (can you guess what color the
bike was?) which I often abbreviate as WKE. It didn’t take me long to make the
choice. The Beast heads were missing the
valves and guides, and had quite small ports to boot. The WKE heads on the other hand were complete
just as I had run them last in the mid 1990’s, not to mention they had
generously sized ports to go along with their 2.100 inch intake valves
(compared to the 1.94’s on the original) and highly reworked exhaust ports.
However, the more highly modified heads did provide one unique challenge. The WKE employed a centrifugal supercharger,
so I had welded in the sides of the combustion chamber a bit to get some squish
from its flat topped pistons. Being
unwilling to start grinding out the welds, thus undoing my many hours of labor
from 30 odd years ago, I set about modifying the pistons to match the
combustion chamber shape.
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30 year old chamber mods
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I began by making a cardboard template of the chamber
perimeter and “tracing” it on to the pistons as closely as possible, followed
by some careful carving on my antique mill.
Then it was it was matter of mocking the engine up more times than I can
count as I crept up on removing the minimum amount possible from the sides of the domes
while still attaining enough clearance to avoid contact when running. So, with the mocked-up engine finally able to
be rotated, I should have been ready to balance the flywheels, right? Well, I admit that with time running short I
did consider calling the pistons good and settling for whatever compression
ratio was left. But my desire to make
the motor as fast as I reasonably could won out. I set up one of the pistons in a cylinder and
used my trusty 100cc burette to measure the dome volume. Just what I had feared, the dome volume and
the resultant compression ratio was significantly lower than what I had hoped
for (under 10:1, if memory serves).
Once again, I found myself welding up the tops of piston
domes. Its not a practice that I would
normally recommend, but what’s a guy suppose to do when money is short and time
is even shorter? So, trusting in the ceramic coating that I would add to the
domes when finished to compensate somewhat for the metallurgical mistreatment
of my welding, I set about adding aluminum until the domes came to a peak. I like to keep an old wrist pin in the piston
while welding in the hope of keeping distortion to a minimum. It assume it helps, but I can’t be sure since I
haven’t tried it without. When finished the pistons seem fine, though I will
add that you want to remove the wrist pins before the pistons cool completely
or they are liable to stick in the pin bore.
Incidentally, this particular set of pistons had received a “Teflon”
type skirt coating back in my serious racing days by a friend who does
industrial coatings. That same coating not only survived whatever torture test
I put them through in the 1980’s, it came through the welding on the domes with
flying colors as well.
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Modified piston domes with ceramic
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After a bit of shaping to the fresh welds, the dome volume
revealed an acceptable 13.75:1 compression ratio (and no easy place to find any
more). After a bit of lightening on the
inside of the pistons under the dome, an oil shedding thermal dispersing
coating was added there, and the balance weights could finally be
computed. No surprise that all of the
extra weight on the crankpin half of the flywheels had to go. Finally, the
flywheels were balanced, assembled and trued! Even with time running out to
make the July 4th deadline, the rest should be relatively simple
though, right?
Not quite.
With the finished lower end firmly bolted into the frame,
the first mock up of the heads revealed even more last-minute work to do in the
short time left. I knew the pipes would
require some fairly major revamping due to the chosen heads having had the exhaust
ports radically re-positioned, not to mention being rectangular in shape. Pressed as I was for time, my backup plan was
to install the short “zoomy” style pipes from the White Knuckle Express that
still hung on the shop wall. The were
too short and probably too large of diameter, but at least they would bolt onto
the heads. That was not to be, however,
despite how much time they might have saved.
The difference between the three rail Truett frame of the White Knuckle
Express and the position of the front down tubes on the stock FX frame meant
that those pipes were nowhere close to fitting The Beast. So, I went back to the original plan of
installing a set of vintage 2” FUBAR exhaust pipes that I had saved for just
such a possible project. They were a dead ringer for the pipes used on the 1987
Beast, but due to the new port location about the first 12 inches of the pipes
had to be cut off with new bends and flanges fabricated in order to miss the
frame rails. Apparently the Lord was not trying to tell me to abandon my quest
to finish in time for the Iowa race, because I managed to scrounge just enough
mandrel bends from a box of miscellaneous tubing I had stashed under a
workbench.
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Rear Exhaust Port
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Front pipe modified and installed
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The intake side of the heads did not prove to be any easier
that the exhaust, though it did catch me completely by surprise. A month earlier I had ordered a couple chunks
of aluminum from which I planned to fabricate adapters to transition the 44
Mikuni carbs to the oval ports on the heads (the width of the oval being taller
than the height). What I had not
foreseen was that the angle at which the ports entered the heads would have put
a good portion of each carb in a space that would be need to be occupied by the
other. That had not been an issue on the
WKE since it had employed electronic fuel injection with the throttle body
before the blower and the injectors (4 of them) just before the plenum style
manifold that attached to the heads.
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Rear head as run on White Knuckle Express
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Back to the drawing board.
I would need to fabricate curved adapters so that the carbs could nestle
side by side as God intended and the laws of logic demanded. The same box of odds and ends that supplied
the pipe to finish the exhaust came through with a couple short sections of
curved steel tubing that matched the inner diameter of the carbs well enough. I was able to shape the inboard end of the
adapters into an oval so that the height matched the heads, but that still left
the ports in the heads wider than that of the adapters by more than I could tolerate,
so I broke out the porting epoxy to fill in the sides of the ports in the
heads. With time running out to have the bike ready for the 4th, I
resisted the natural urge to put the heads back on the flow bench to see
exactly how the impromptu port shaping had affected things.
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Curved carb adapter in place
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With less than a day to go, I was finally ready to bolt the
heads on – or was I? The final squish
distance of .037”, piston to head, was based on no base gaskets (a light coat
of sealer) and no head gaskets. The now vintage Axtell cylinders sported a
groove so I just knew that all I needed to do was install a copper wire
into the groove, add a little “Copper Coat” as insurance, and torque them down
as I had done many times in the distant past.
Oops. Turned out that these
cylinders, being the last that I purchased (nearly 30 years ago) had what was
then the latest technology, meaning the groove was the correct dimension for a Viton
o-ring rather than copper wire. Needless to say, it had been decades since the
last time I had a set of these o-rings in stock. But with time fleeting, I took a few
measurements and found that early inner primary to crankcase o-rings were the
correct thickness, though I had no idea if they are of a suitable material. Since the heads had previously been lapped to
the cylinders, I didn’t waste any time second guessing myself and went ahead
and installed primary o-rings shortened with a diagonal splice.
On Thursday afternoon we were able to do the initial fire up on The Beast, with time left over in the evening to load everything and still
get a bit of sleep before the trip to Humboldt and time trials on the next day.
So I guess that overall, you might say
that getting the replica Beast finished up in time was just another routine
build for the average drag racer.
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Or, how we got from this ...
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... to this
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