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1974 Ducati 750 GT Custovation
Diary
1974 Ducati 750 GT Bevel Head
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Special Report by Joe in Dallas for webBikeWorld.com
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1968 Royal Enfield
During my years of riding, restoring and collecting
vintage British and European bikes, I fell in love with
four distinctive vintage marques.
The muscular engineered Vincent Rapide; the
gentlemanly smooth Ariel Square Four; the petite and
potent Velocette Venom thumper and the Ducati 750
V-Twin, an Italian blend of engineering, power and
seductive good looks. I’ve owned 3 of the four
with the Vincent being out of financial reach.
Each machine materialized from the minds of great
designers. Phillip Vincent’s HRD-Vincent, Edward
Turner’s Ariel Square Four, John Goodman’s Velo Venom
and Dr. Fabio Taglioni’s Ducati bevel drive V-twin. All
share common attributes of distinctive style, power,
sound and engineering excellence for their day. Sadly,
three of the four have passed to oblivion but Ducati’s
legacy of efficient and practical design lives on in the
GT1000 SportClassic, the grandson of the ’74 bevel drive
V-Twin.
This diary captures the high points of finding,
owning and "custovating" a 1974 Ducati 750GT. Custovation
is my word for customizing and renovating the build of a
one-of-a-kind vintage motorcycle. The custovation
captures the heritage of the early 70’s bevel drive
racers and adds some modern and personal touches to make
the bike reliable and safe ride at speed, while
maintaining the head-turn factor. This diary is a
completely selfish act to preserve the details of the
750 GT custovation events that took place before, during
and after with the notion that it inspire or guide
others to develop their own custovation project.
In the Beginning
The project bike, a 1974 750 GT was purchased in 1997
from a Norton club friend and he acquired it at an
estate sale.
It sat in his garage for two years before
the need for more room encouraged him to sell. The bike
was about 95% complete and in fairly good condition
since the Texas climate and the storage inflicted
minimal damage. After acquisition, it sat in my garage
for 5 more years, waiting patiently for the start of the
project.
During the waiting time, some missing bits were
purchased. A lot of tinkering about personal
preferences, color schemes and technical issues were noodled around in the gray matter design room between my
ears. For inspiration, a montage of Ducati bevel drive
V-twin pictures was hung on the shop wall serving as a
project compass pointer. That’s the day the flag
dropped. In my mind's eye, I was able to clearly see what
the bike should do and how it should look.
The Custovation specs called for a style taken from
the genes of the café style bevel drive V-Twins but
without the lay-down riding position. Ace style bars and
a mono-posto seat with a bum-stop add to the look. Stock engine performance, new suspension, ignition and
modern front disc brake system take care of the go,
handling and stopping chores.
Oh yeah -- it should also borrow
the colors that made the 1974 750SS forever famous.
The project was divided into two stages; the frame
and all its associated components including electrics
and then the engine. I learned the hard way that it’s
better to break a long project into manageable chunks.
That way, tasks are smaller and have a defined start and
finish along with a logical fit with other assemblies of
the project. Motivation is fueled when you see steady
progress, while the expenses are stretched out.
Before any work was started several information
sources were consulted. A collection was made of
downloadable manuals, article reprints, picture gallery
and parts sources from around the world. Bevel Heaven
offers additional information and their parts inventory
continues to grow. Various hardcopy reference books were
useful too and they’re listed at the end of this
article. Most can be found on the net or from bevel
drive specialist’s shops.
Take-Down
In February of 2002 the motor was started for the last
time before the take-down.
The rationale: if the engine
runs before it’s taken apart, I know it will run after I
put it back together. The removal was very easy and the
engine was set on a dolly until the rolling frame was
complete. I imagined a gleaming rolling frame with all
parts fitted, anxiously waiting for the engine. Just the
kind of inspiration needed for an expected 8-month
project.
The speedometer showed 35,000 miles and the Smith’s
instruments appeared original, so it’s very possible the
reading is accurate.
Compression was low on the front
cylinder and fair on the rear. Someone fitted a Dyna –S
electronic ignition so a good battery and a squirt of
oil in the cylinders, helped get it going.
No blue smoke
so maybe the guides or valves are not worn. The answer
to that question will come later. Even in its weakened
state the neighbors confirmed that the old bevels drive
V-twin’s bark sounded awesome without silencers.
Disassembling the bike down to its major component
parts was easy and in a few hours there were several
boxes of parts organized and tagged as needed, so three
months from now I’ll be able to recall where that weird
bolt is supposed to go.
Tiny ferrous metal chips are a tough to remove from
the magnetic rotor. Left in place they can cause major
damage to the stator. So as soon as the alternator cover
is removed from the bike, cover the magnetic rotor with
plastic wrap and tape into place -- this will keep any
ferrous chips and debris from collecting on the rotor.
Examination of the removed parts revealed the
tachometer to be broken, sprocket and chain completely
worn, tires while showing deep tread, felt like wood
instead of rubber. I had to cut them off with a hacksaw.
.
Wheel bearings either worn or seized, stock Scarab
caliper seized, J-model master-cylinder a useless
insult, front wheel bearing spacer worn, swing arm
spindle rusted, front fork seals leaking, carbs in need
of rebuilding, air cleaner plastic box disintegrated,
front and rear brakes worn out, Lafranconi silencers
more at home on a Guzzi, frayed cables, outdated shocks,
the electrical system showed the tell-tale signs of
being tinkered with in the past 28 years. Tape balls,
green oxidation and extra wires sprouted from the loom.
Several days were spent cataloging replacement parts
and their estimated cost. Pills and meditation had
little effect to lower my blood pressure, as the
estimated price tag for the parts was revealed.
This
step is like having a colon exam. You volunteer to have
it done but all the time it’s embarrassing and no fun at
all. So orders were placed, checks were written and bank
accounts were emptied. I kept telling myself
"This is
the price to pay for custovating a vintage bike".
With the easy tasks behind, it was time to get
serious. This is the part of the project that’s labor
intensive, so no matter how much time you estimate it
will take, it will take longer.
 For inspiration, I wanted to get something pretty in
the garage faster than you could say pasta primavera.
This is where paint and polish gives an adrenalin rush
and accolades from your friends. The frame had some rust
and grainy paintbrush touch-ups. After a valiant effort
to strip the old paint and remove the rust, I gave up
and a professional sand blaster removed all traces of
rust and old paint. Best money spent.
The steel frame
and trim parts had the ideal textured surface for paint
adhesion. The painter was already on board wa iting to
receive the blasted parts for primer. The colors, decals
and trim scheme were worked out ahead of time so he knew
what to do.
While the painter was busy, parts cleaning and
polishing started with a vengeance. Polishing aluminum
is the dirtiest job on the project but it yields the
best rewards. For the next few days my nose sneezed out
more aluminum oxide dust than a smelter but the end
result produced alloy parts that gleam like chrome. Only
the kick-lever, gearshift, rear brake lever and stay arm
will need a trip to the chroming vat. All rough finish
cast aluminum parts get a trip through the blaster.
After blasting, I usually go over the castings with a
stiff stainless steel brush to bring out a long lasting
dull but resilient patina
The stock spokes were painted silver, with thoroughly
rusted nipples. If you rebuild your own wheels, remember
to photograph the lace pattern. Measure the hub offset
before cutting off the spokes. I forgot that on the rear
wheel but confirmed with others that in fact the hub is
centered on the rim.
 As the parts orders arrived and the alloy jewels
emerged from buffing wheel, they’re collected in boxes
designated for reassembly. Having the majority of the
parts in-garage before the build-up starts makes the
workflow resemble an assembly rather than start, stop,
wait and repeat again.
Surprisingly some of the stock hardware was not
rusted due to what appeared to be heavy nickel plating. Big pieces like spacers and large nuts polished up very
nicely from a battleship gray to a bright finish.
Throughout this custovation, every fastener was
replaced with stainless to the extent possible. Bolts,
nuts, lock washers, lock nuts, and locking nuts,
including the engine cap head screws.
Stainless wants a
smear of anti-size compound on the threads before
assembly to prevent galling. For appearance and
longevity, stainless can’t be beat. Buying stainless
hardware from a wholesaler is about one tenth the cost
from a hardware store but not as convenient.
Build-up: Frame Parts
The paint scheme follows in the footsteps of the 750
Super Sport, blending the distinctive silver-gray
background with duck egg green. I wasn’t interested in
building a SS replica, so while the frame is drenched in
green; there is no fairing, clip-ons or rear-sets.
The
stock steel tank’s voluptuous shape begged to have the
side panels painted green so the new die cast DUCATI
emblems would have a place to contrast. The fenders were
painted in the same style with a green stripe down the
center. The side covers sport vintage Ducati eagle logs
and everywhere where green and silver meet, a fine black
stripe defines the transition.
Wheel lacing was a gift from my Dad. He showed me how
on bicycle wheels, when the dinosaurs roamed the earth.
I’m no expert so I work slowly and it comes out right. There is nothing like lacing stainless steel spokes to a Borrani rim fresh from the buffers kiss. It’s a
beautiful sight. During assembly, wear cotton gloves to
minimize fingerprints and sweat deposits and use the oil
provided, to prevent the nipples from galling.
 A long while back, I made a simple spoke wheel truing
stand that looks homemade but gets the job done. After
the wheels were built, Avon Super Venoms with new tubes
were mounted easily and look good. In the hubs, the
wheel bearings were either seized or grinding, so all
bearings were replaced with sealed units.
To keep the racer appearance the stock rubber foot
pegs were replaced with knurled pegs with a clear
anodized finish.
The Marzocchi front forks were next. The leading axel
fork legs have an exotic look. Cleaned, polished and
with new seals and caps, the cast Ducati logo proudly
shines on their sides.
The swing arm spindle seemed snug during the
take-down. However, when it was removed and the rust
cleaned away, it shrank, causing the swing arm to
develop enough play to cause concern about handling
stability. A new spindle solved the problem and modem
shocks with chrome springs connected the back of the
swing arm to the frame.
The stock banana seat was in good condition but I
wanted a café look. I had it reshaped and covered by a
local custom car upholsterer. He cut down, then built-up
the foam to produce the classic shape of a bum - stop
seat. The custom fit cover has DUCATI embroidered in
black on the back panel.
A used stainless chain guard was acquired and
polished to cover a low maintenance O-ring chain running
on new steel sprockets.
The voluptuous gas tank required new rubber isolators
and water-pipe neoprene foam insulation coved the
backbone to give the tank a cushy place to rest. A large
O-ring secures the tank to the frame nubs
This 750 GT came from the factory fitted with
Lafronconi silencers. They were too quiet for my taste
and lacked the SS look, so Bub’s Conti replicas were
fitted. They’re not Conti’s but are half the price and
look and sound just as good.
Dr. Taglioni figured that one disc brake was enough
to stop the 750GT with a stock engine and I’m not one to
challenge his genius. However, this bike is from an
early production run and was fitted with a solid rotor.
To add some style, I drilled a curved pattern of
large and small cooling holes in the disk. The Scarab
caliper was seized and parts no longer available. So a
bolt-on Gremeca caliper fed by a Brembo master cylinder-switch-lever combination was fitted.
If you have an
opportunity to refit the master/caliper combination on
any bike, be sure to check sources so the two pistons
and travel are matched for braking performance,
otherwise you’ll have a very poorly performing break
system. A Ducati Monster clutch hose completes the front
stopper system. Bleeding the dry system was more trouble
than expected but a Mighty-Vac solved the problem.
The original pair of 30 mm Dell’orto carbs was
rebuilt and K&N filters added to prevent anything but
air from visiting the inside of the combustion chamber. The crankcase breather is also capped with K&N.
The bars are Ace clubman style turned up-side down to
relax the seating position and fitted with new
electrical controls and tacky black grips. During the
Build-Up, plastic bottle caps are taped to the bar ends
until the grips were mounted because I almost ripped
open my scalp with the bike on the lift.
The rebuilt Smiths instruments looked like new with
the intention to keep them that way for as long as
possible. Prior to about 1970, shock and vibration
failure must not have been a concern because this type
of instrument secured directly to the mounting bracket,
which was bolted to the triple clamp.
After that,
various types of shock mounting were employed to keep
the innards of the clocks from self-destructing. The
stock Aprilia mount goes the other direction and uses a
comprehensive isolation design, hence the big, ugly pod. After 1970, Triumph and BSA instruments were fitted with
rubber cups. That type of mounting appealed the most to
me since they’re readily available, reasonable price and
they fit nicely into the fabricated instrument holder.
To hide the backside of the instruments and add a bit
of modern sleek, a AGIVI A-200B smoked mini-windscreen
visually pulled together the headlight and instrument
package while adding a stylish wind deflector for the
rider.
Electrics
Wiring posed its own array of challenges. For the most
part the brass connectors were oxidized but otherwise
sturdy so cleaning was only a wire brush away.
Since my
electrical functions were a bit different than stock,
some wires were removed or added to the harness. Marine
grade multi-strand wire is the best choice for this type
of application. More strands mean more flexibility and
that translates to connections that won’t break apart.
A
modern style integrated horn, headlight beam selector,
turn-signal switch was used in place of the worn out Aprillia switches. The Brembo master cylinder has a more
reliable micro-switch to operate the brake light so the
pressure activated switch isn’t needed.
All new wires
were tape wrapped or sleeved for abrasion resistance and
maintain a clean look. The final step was a live
electrical test with the battery connected. What a great
feeling to see the lights work and voltage show up at
the proper places, the style and character of the bike
shown through!
The headlamp assembly used the stock headlamp since
al halogen would add more drain to the weak charging
system. Mounting the headlight shell was a delicate
matter of looks and proper fit. Be aware that the
clearance between the forks and gas tank is limited, so
the new aluminum Tomeselli like support brackets were
used.
Turn signals are Lockhart Short Stalk-V’s. The rears
are mounted near the shock tops while the fronts are
mounted in the headlamp brackets.
The stock horns worked fine but looked large and out
of place here, so an aftermarket single unit with chrome
face was installed, more for looks than sound power.
One of the more difficult tasks involved the layout
and appearance of the instrument / ignition key /
indicator lights. I wanted the key conveniently located
next to the speedo, tack and the two indicator lights
(turn-signal & high-beam). The stock instrument pod is
large and ugly.
So the remedy was a custom cut and
polished aluminum plate that mounts in the same place
but brings the instruments closer together and tilts
them toward the rider.
Cutting the plate is actually
very easy, but there was a lot of pre-cut fitting,
measuring, guessing etc. Cover the plate with wide
masking tape to protect the surface while marking and
cutting. The end result turned out to be a very good
match for the polished clamps and chrome bars.
The voltage regulator and connector panel were
cleaned, tested and painted. There’s a lot written about
the weak charging system on the early bevel heads and
it’s all true.
The best solution is to replace the rotor
and stator with untis from a late 90’s ST-2. However,
that’s also a thousand dollar plus fix. With the
guidance of Willy Gonnason’s expert advice and
engineering, I opted to rebuild the regulator with
modern semiconductors and install a LED charging
indicator. This works well for me since the majority of
my riding is during the day.
The original ignition switch was damaged, so a new
small automotive unit was wired in but moved to the new
instrument panel for better access.
The switch is
compact and since it has only three positions switching
options are simplified. Off, On – with all but the
headlights powered and the other On- adding power to the
headlights.
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A
Restored 750 GT Engine. |
A previous owner, installed a Dyna-S ignition, but
kept the stock coils. One coil was found to be open when
the start-up was attempted.
A replacement was used then
but for about the same price, modern matching high
output Dyna coils were installed ensuring a healthy
30,000-volt lightning bolt to zap the gas vapors.
A
homemade aluminum bracket tucks them smartly under the
gas tank with outputs pointed down. Resistive plug wires
are from NAPA and plugs from NGK.
The battery is a slightly larger capacity 14 Amp Hour
unit to ensure enough power for the bike. The battery
compartment base was lined with a piece of spongy
doormat material so the battery bottom wouldn’t chafe on
the metal mount. Large O-rings or rubber bands cut from
an inner tube work well as elastic hold-downs.
The rolling frame with electrics was finished, so the
engine is next.
The Engine
INSPIRATION. That’s what’s sitting in the garage.
The
parts are mounted, wiring harness connected and tested
multiple times. Yeah, I even shut off the shop lights to
see what she looks like during nighttime ride. The
complete rolling frame is ready for the engine
First things first. Since the true condition of the
engine internals is unknown, cleaning was a good place
to start. That way, if the bottom end and gearbox are
ok, that portion of the engine will be ready when the
top-end rebuild is complete.
It’s easier to clean the
outside of the cases with the top end installed but the
huge glob of congealed electricity (read: aluminum) is
clumsy to handle.
The bottom cases are scrubbed with carb cleaner, Simple Green and S-100. Use either a
stainless steel or hard plastic bristled brush but not
brass. Brass leaves a yellow patina that’s difficult to
remove.
All the smooth case pieces will have their oxide
veil removed and replaced with a brilliant mirror like
finish after the buffing wheel plants its kisses. A nice
surprise was hiding on the bottom of the engine -- the
factory case seal was still in place, saying that no one
has been in there for 28 years.
Removing the heads was easier but the cylinders were
stuck and didn’t release when the heads were removed.
Squirting some WD-40 down the cylinder stud holes and
applying some propane torch heat and soft mallet to the
base immediately released the cylinders.
Be careful
where you strike, so the fins don’t break off. The
sticky culprit was a rust build-up right at the place
where the stud exits the case. The rust made a bulbous
deposit that held the cylinder from easy release. I
suppose that condensation and external seepage under the
stud nut allowed the water to do its nasty work on the
stud. I spritzed a little WD-40 and held a big magnet
next to the glob while scraping. A stud remover tool was
used instead of vise grips prevent tooth bite damage to
the studs.
Anxious to understand why the front cylinder had low
compression, revealed that the lower compression ring
was stuck solid in the piston. The smallest trace of
rust was acting like barnacle glue. The rear piston
assembly, looked good and both bores while shinny had no
scoring or notable ridge.
The piston bodies appeared to
be in very good shape with little carbon buildup. The
first try to remove the stuck ring simply didn’t work. Freezing, then heating
and oiling had no effect.
Then Syd of
Syd’s Cycles suggested heating the area behind the ring
on the thick inside of the piston with a lot of propane
heat. That did it. Picking at the ring made it break
into several pieces leaving the piston unharmed. That
was ok because the prime concern was for the piston
since fresh rings were in the re-build plan anyway.
In the end, it was a waste of time. Measuring the
allowed wear parameters of the pistons, bores and rings
confirmed that first over pistons with matching bore are
needed. That confirmed that the engine very likely has
35,000 miles on it. With that expensive fact in mind,
new valves and guides were also fitted to refresh the
top-end.
Cleaning the heads and cylinders involved bead
blasting. There’s a lot of debate on this cleaning
method. Some say hidden grit will immediately kill the
engine. Grit is bad for sure.
On the other hand, my
experience has been ok in the past. My drill is before
blasting: 1) degrease the entire thing then dry; 2) Wire
brush clean the sensitive mating surfaces of the head; 3) Tape over the cylinder bores and various
cavities and holes leaving only the fins for blasting;
4) After blasting, clean with high-pressure air followed
by a thorough second degreasing; 5) The raw casting can
then be either steel wire hand brushed to bring back a
hard finish with bright patina or final cleaned with
S-100 and a stiff non-metallic brush for a softer
finish.
Since the engine cases were not split, two internal
items needed sprucing up. First, both sludge traps were
cleaned. A small butterfly impact wrench works best to
remove the slot head screw caps on the crank. There was
plenty of packed-in carbon / metal hiding in those
holes.
Using a dental pick and solvent sucked by a shop
vacuum, emptied them out. Second was the sump and
gearbox sludge removal. Kerosene poured in the cylinder
holes and oil filler hole worked like a charm. Actually
the process was repeated several times until the drained
kerosene is mostly clean. A small rag on the end of a
parts grabber went inside the oil and filter holes to
move things around and eventually soak up any excess
kerosene.
 The clutch case bearing was replaced and cover
polished along with the alternator side cover. The
gearbox selector case was opened and cleaned and
re-packed with moly–graphite grease. These three cover
pieces play a big role in defining the beauty of the
Bevel Twin engine, so no polishing effort was spared.
The side stand wasn’t used so the engine stud was
removed and replaced with a suitable length engine case
bolt.
About this time, the top end parts list was made up
and shopping started. I should have had the paramedics
standing by when the first quote came in. I figured it
would be expensive but when the prices came in, my blood
pressure dropped and my vision went white. This of
course is perfectly natural reaction unless you’re Bill
Gates. I had just crossed the Rubicon with this project. There’s no stopping now, especially when it’s just money
posing as a roadblock.
The ignition points housing was polished in-place to
not disturb the gear timing. The steel bevel drive tubes
looked like two rusty drainpipes so they were replaced
by an anodized set from Dr. Desmo.
Both carbs were given a full cleaning and polishing
with fresh rebuild parts. Cables are replaced and the
choke junction box was freshened up. The choke plays a
critical role to make for easy starting.
Guides and valves were replaced along with all the
head bearings. The left side bearings were replaced with
sealed units, with the exterior side seal removed to
boost valve train oil pressure.
The cylinders were bored to the first oversize and
mated with beautiful looking JE Pistons. They have a
shorter skirt and taller dome than the stock pistons. That taller dome should raise compression just a tad.
Putting it Back Together
The engine top-end is a puzzle of engineered aluminum
and steel but now it’s time to assemble the bits.
A temporary assembly was made first to see the main
parts fit together and measure the valve to rocker shim
sizes before fully mounting them.
 The cylinders were installed on the engine cases
first but without the pistons. However, before that, the
case-mounting surface was cleaned and the stud holes
de-burred to ensure a flat mounting surface.
The stud
holes had crud living inside, bits of alloy, steel, rust
and oil grunge. A small magnet, dental pick and
high-pressure air cleaned the holes like new. Anti-seize
was applied to the stud threads.
Before installing the
gaskets, notice that the front and rear gaskets are cut
to match the case holes. Get them reversed and you can
kiss the engine good by.
Pistons were then mounted on the connecting rods. The
small end bush was lightly roughed up with emery cloth.
My clips had no tang to grab so installing them was a
pain.
A test fit of the cylinders and heads, revealed one
of the rear cylinder fins cast below the exhaust port
was a bit too long and made contact with the cylinder
fin, when the head was mounted. The cylinder to head
joint does not have a gasket, so the head seal depends on the
machined metal-to-metal joint for a seal. It looked like
a manufacturing flaw since the neighbor fins where cut
down for clearance. Maybe Giuseppe the inspector
had a bit too much Chianti for lunch that day? Some grinding
shortened the fin and made the seal tight.
New bearings were installed all around in the heads
for a rocker to valve clearance test. Note that the four
rockers are identical but can interfere with each other
if not installed correctly. The rocker springs need to
be opposite of each other to properly center the rocker
on the cam. Check that the rockers are centered on the
valve stem. Both of my exhausts were off by .012, so
additional shims were needed to get them centered.
With new valves and re-ground seats, new valve caps
were needed. There’s no screw adjustment on the early
750 GT’s, only fixed space caps. Measure the gap with a
stack of feeler gauges to determine the gap of
interference, then, order caps that are thick enough to
grind down to the correct valve clearance value.
When
measuring, make sure the cam is seated next to the bevel
bearings otherwise the measurement will vary and the
caps won’t fit. I replaced my old Vernier calipers with
a digital readout unit for about $30. Best investment
ever, and the only way this job can be done.
Installing the built up heads takes some
consideration. I was momentarily stalled because it
wasn’t immediately obvious how the front head fit. All
the books and articles written about rebuilding the
Bevel Head only talk about installing the rear head. There are no details about front head installation.
Installing Bevel Heads
Here's the drill: Align all the engine gear dots. That's TDC for the rear. Mount the rear head. With its cam and
gears installed (with its dots aligned) its at TDC
already. Fasten it down to 30 ft lbs.
Then take the
front head: with the rockers removed, install the cam
and vertical drive, aligning their dots. Snug tighten at
this time. Rotate the cam so the lobes are at 4 and 8
o'clock, (that's TDC for the front) then mount on the
cylinder. It fits right in. Fasten head bolts to 30
ft-lbs. Then install the rockers, mount the cam bearing
support. Secure the cam nut lock washer now.
Setting the proper torque for the head bolts is
another dilemma. Torque spec is 30 ft-lbs, however,
there’s no room for a conventional socket-end torque
wrench. Only an open-end wrench works. Having no other
alternative, I practiced to get the feel of 30 ft-lbs. I
clamped an old bolt with nut in the vise and tightened
with the torque wrench then the same with the open-end. A few times back and forth and I think I got a feel for
the torque needed.
At this point the engine was finished enough to mount
in the frame. The side covers were not installed yet
since they’ll get in the way. Mounting the engine is a
breeze -- three bolts and that’s it.
Light at the End of the Tunnel!
A genuine simulated gold link O-ring chain made sure
those Italian ponies make their way efficiently to the
rear wheel. The drive chain on bevel drives has a
tendency to score the engine case so this was a good
time to fit a Case Saver form Bevel Heaven. Mind the
instructions to locate the saver in the exact spot. When
it’s there, the chain has a clear path above the cast
alloy housing.
I removed the Dell’Orto chokes to simplify the engine
layout. I learned that for easy one kick starting the
choke is needed. The original setup uses a square metal
box as a junction place. My cables were worn and I
didn’t want to locate the choke lever on the handlebars,
so I used an Amal 2 into 1 throttle connector. The
cables were replaced and an Amal choke lever located
under the right side of the tank. And guess what?
The bike starts on the first kick now!
Adding the freshly polished alternator and clutch
side covers was like jump-starting a flat-line heart
failure. The bike seemed to pop to life. Not a full,
hop off the table jump, but the kind that makes the
paramedics grin when they know the patient took their
first step toward a new life.
Finished at Last
It was about this time the 750 GT acquired a new name:
The Texas Duke.
The first start-up of the Duke was a momentous occasion. I made this a family event since my infinitely patient
wife, Beverly, and our family of sons, daughter,
grandchild and their spouses, all have an interest in
riding. They all appreciate fine vintage machinery and
art in their own way. So one Friday evening we assembled
in the garage for the Duke’s début.
There he sat a dandy in alloy polish splendor. Sporting
new pistons, rings and valves, along with modern
technical refinements like electronic ignition, fine
Italian brakes from Brembo, the SS like paint job,
stainless everything that can be stainless and tires
from the land of Avon.
He was welcomed back into the world of two wheel
motor-sports with a hearty SALUTE’! We toasted fine red
Italian wine from the vineyards near Bologna while
Andrea Bocelli sings in the background. This small but
faithful group of Italian motorbike lovers cheered, Benvenuto a la Duke!
He cleared his throat of fresh oil
and Lubriplate. Another kick and he roared back at us
just as I expected him to. Loud, authoritative and
commanding a presence in the garage, I’m The Duke and
I’m BACK!
What a beautiful Bevel Head -- a sight and sounds to behold. Just like seeing your kid receiving a college diploma.
All the hard work and expense paid off, cigars were lit
and smoke rings filled the air.
One more toast, to Dr.
Fabio Taglioni. He’s gone but his spirit will remain an
inspiration to Bevel Head lovers and the Texas Duke.
► 750 Bevel Head Rebuilding and
Restoration Tips
Some pointers that may save you time and effort
rebuilding a Bevel Head
Ignition timing (with Dyna-S Ignition)
Tools Needed:
• Indicator light
• Piston Stop tool
• Degree wheel and wire pointer
Rotate engine to just before top dead center - the
exact distance is unimportant, then screw your tool into
the cylinder head, unlock the locknut and thread the rod
down until it touches the piston crown, relock the nut.
The important part is to stop the piston going over TDC,
then place your degree disc on the crankshaft and fix up
a pointer in the normal manner. Next turn the disc to
where you think it should be, again accuracy is not all
that important at this stage, next turn engine so that
the piston is hard up against the rod of your TDC tool.
Now look at your degree disc, say it reads 42 degrees BTDC
(before top dead center) make a note of that figure, now
turn engine backwards until piston rises and contacts
the TDC tool once again. Holding in hard contact
look at degree disc, this time say it reads 18 degrees ATDC (after
top dead center).
Now comes the interesting part, add your first
reading (42 degrees BTDC) to the new figure (18 degrees ATDC), resulting in 60.
Now divide 60 by 2 and you have 3O degrees so still
holding engine against the stop move your degree disc to
read 30 degrees ATDC, to check if you are correct,
rotate the engine forward again until the piston
contacts the stop and check the disc - it should read 30
degrees BTDC.
Next, remove TDC tool and turn engine till disc reads
0 degrees; this will be true TDC. Easy isn't it?
But just in case, another example: Engine contacts
stop at 61 degrees BTDC, turning the engine back the
other way stop contacted at 33 degrees ATDC. 61
plus 33 = 47 degrees. So set the disc to 47
degrees ATDC to check, rotate the engine
backwards and the reading should be 47 degrees, BTDC.
Remove
tool and set engine to 0 degrees as indicated on the disc. As will be seen by the above, the action of holding the
piston hard against the stop from both directions
removes any inaccuracies due to the various engine
clearances. This results in a true TDC impossible to
reproduce by other methods.
Note: For beginners, the Ducati Bevel drive twin runs
backwards, so don't get your BTDC and ATDC confused.
Rear Brake Cable
To ensure smooth rear brake return
action, make sure the foot lever cable point is lined up
with the frame cable stay. The cable should travel in a
straight line out toward the rear wheel. If not, heat
and bend the foot lever cable lever to line up. Next I
used a rubber coated cable clamp large enough for the
cable to pass through. This was located the left
silencer mounting bracket. It keeps the cable running
straight for about 10 inches.
Rear Brake Light Switch
The switch that’s mounted on
the cable is useless and not easily removed. I replaced
its function with a universal rear brake light switch by
drilling a small hole in the foot lever cable lever for
the spring to attach. The other end is mounted using a
rubber cable clamp to the frame tube holding the
silencer bracket.
Slipping Clutch
My bike had been sitting unused for more than 6 years. I
left the clutch alone during the rebuild waiting to see
what it needed once it was road worthy. Sure enough,
even though the slack adjustment was correct, the clutch
slipped under acceleration.
Examining the steel plate
and friction plate stack, the thickness was greater than
1.19 inches per the wear spec so I assumed it wasn’t
worn out. The friction material showed that the surfaces
appeared glazed but not from use, rather something was
on the surface.
So I washed them in solvent. Very risky
but I was sure it wouldn’t hurt the material and not
leave any oily residue like kerosene. Sandblast the
metal plate with 100-grit aluminum oxide. Place the
plates on a flat metal surface while blasting to prevent
warping then replace the springs with a heavier coil
than stock.
Valuable Ducati Custovation Resources
Bevel Drive Twins and Ducati Restoration Books
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