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MOTO
GUZZI V7 SPORT CLASSIC RACER
You may have seen
photos of David McMillan's V7 Sport racer dotted about the web
- luckily he contacted me and I'm really happy to post some superb
pictures of this beautiful bike, and a description in David's
own words of what has been done to build this beautiful and powerful
Guzzi - it has to be one of the best looking Guzzis around. I
hope if I ever make it to Scotland he'll let me have a ride, and
then I'll write up a roadtest. More Guzzi racers coming soon-
Adam
click
on the thumbnails for a bigger picture
"This
machine is a version of the 1971-72 V7 Sport production racers
which had a capacity of 748cc (82.5 x 70mm) down from the production
capacity of 757cc V7ís to enable participation in the 750cc racing
class. It is the immediate descendant of the 1969 V7 loop frame
team which set class records at Monza. Introduced at the Milan
show the V7 Sport was first seen in competition at the 1971 Monza
500km meeting, with Riva taking 3rd.
The
template for my machine is the Imola bike of that year reputed
to produce 80bhp and capable of 140mph. Moto Guzzi subsequently
entered a number of endurance events in 1972-3 during which the
embryonic 844cc Le Mans engine was developed. Like other endurance
racers of the time the Imola race was for production framed machines
and although not specifically designed for, nor entirely suitable,
for short circuit racing my V7 Sport meets the parameters of the
Scottish Classic Racing Motorcycle Club eligibility rules. It
is classed Group 2, period 2, unlimited capacity. It could also
run in the production class but as there is no other bike in Scotland
racing without a modified frame it would be a lonely and pointless
exercise. I researched the history exhaustively due to resistance
in the club as they feared a modern BOTT firebreather dressed
up in classic clothes.
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"they
feared a modern BOTT firebreather dressed up in classic clothes"
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I was able to demonstrate the existence of a 1972 triple disc,
link-braked,40mm carbed V7 Sport confusingly labelled Le Mans.
The regulations stipulate standard frames and swing-arm of the
period. Wheels must be 18inch wire with period brakes, forks,
carbs and must maintain the appearance of the period. Engine and
gearbox should appear externally as they were originally (such
as correct head finning and gearbox crossover tube) but internally
are free for development. I took advantage of the easily accessible
tuning parts off the shelf and wanted initially to build reliability
not a hand grenade so the tuning is pretty mild. The outcome was
the result of much research into the specs of Guzzi race bikes.
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The outcome was the result of much research into the specs of Guzzi
race bikes. |
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Fortunately Classic rules informed the majority of the constraints
and therefore financial outlay. The motor is 992cc, 90 x 78mm,
11.1 compression. The crankshaft has been fanatically polished,
lightened and dynamically balanced to a reciprocating factor of
52%. Carrillo con-rods with 90mm slipper pistons in Gilardoni
Nikasil barrels require the crankcases to be machined to fit.
The sump oilways were also enlarged to 11mm from 8mm and replugged
to match the upgraded oil pump which has 16.5mm gears compared
to the original 14mm. An 1100 Sport oil filter was adopted for
its increased capacity and less restrictive flow. A ventilated
sump spacer helps reduce crankcase pressure and because it has
a horizontal plate prevents the crank rotating in oil when leant
over cutting resistance and sublimating foaming. An Agostini crank
breather box is utilised and is extremely effective in eliminating
froth from pressurised oil.
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A
relatively mild P3 cam was employed with 1100 Sport pushrods
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A relatively mild P3 cam was employed with 1100 Sport pushrods with
upgraded valve springs restrained by standard alloy valve collars.
44mm and 37mm valves were selected for their torque rather than
speed offered by bigger valve heads and the ports were polished
and modified to match 40mm carb inlet tracts. The combustion chambers
have still lots of scope for modification. The heads are dual plugged
with an additional 10mm plug added to the combustion chambers blind
side. It revs to 8,000rpm before valves start to float. Dyna 111
ignition with Dyna 3 ohmn dual plug coils and Dyna silicon HT leads
have been without fault but are very sensitive to earthing direct
to cases not powder-coated frame. Timing gears were tried but the
gears were binding as the crankcases must have been machined incorrectly
so a tensioner and chain are used. |
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"40mm PHM Dell'Orto pumper carbs similar to the PHBs present
on the 1972 Imola Ducatis"
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40mm PHM DellíOrto pumper carbs similar to the PHBs present on the
1972 Imola Ducatis were permitted after much debate and I keep the
accelerators connected. A Tommaselli 2c throttle works the cables.
A RAM ergal alloy flywheel and single plate diaphragm clutch with
a deep spline centre is connected to gearbox with 1100 Sport straight-cut
three dog cluster. This dramatically reduces inertia making gear
selection smoother, pick up out of corners swifter and most vitally
is less prone to locking up during down changes. The three dog selector
means keeping a hold of third gear at speed is more likely. I
used the updated UJ which is now an interference fit with the swing-arm
bearing and is a pain to fit and have the choice of bevel box ratios
giving different gearing characteristics 7:33 (most 850 and 1000),
8:35 (V7 Sport), and 8:33 (Daytona) giving 120mph, 130mph and 138mph
respectively. The swing-arm has an under-slung and braced horseshoe
tubular brace, triangulated to reduce flex. I also scalloped the
drive tunnel to allow wider tyre fitment up from 2.15 to 3.00. The
front section is up from 2.15 to 2.5 and I use Avon AM23 130/70
rear and Avon AM22 110/80 front VB260 sprint compound, which sounds
sticky but is actually for road use although race compounds can
also be bought. Galvanised spokes are laced to Akront deep flanged
rims, stainless spokes have a tendency to shear catastrophically. |
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Hyperpro progressive fork springs give
a sophisticated ride
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The rear brake calliper mounting plate is no longer restrained by
the swing-arm tab and initially fixed to the centre-stand tab via
a dural tension rod and rod-end bearings allowing a fully floating
support plate to rotate and beneficially placing the calliper weight
below the spindle. Brembo Goldline callipers with illegal asbestos
racing pads (does anyone know of a suitably soft modern racing equivalent?)
are secured by dural mounting brackets to Marzocchi M1R 40mm forks
offering un-adjustable rebound damping in one leg and compression
damping in the other. Hyperpro progressive fork springs give a sophisticated
ride. I have used undrilled and unskimmed cast-iron discs with Goodridge
stainless steel brake lines retaining the linked braking distributor.
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California 1100i yokes with the original shorter stem pressed
in and a dural fork brace keep the forks in line with a stainless
special spindle. The forks were dropped until the sump was parallel
with the ground without anyone on board, helping turn-in and lowering
centre of gravity. I fitted a White Power steering damper mainly
for road bumps that the stiff track suspension doesnít like. White
Power rear shocks 13.25 inches long (same as Le MansV length for
longer swing-arm) lift the rear end higher without stressing the
UJ too much, again quickening turn-in and increasing ground clearance
but have adjustable rebound damping only as external compression
reservoirs are not permitted in classic racing.
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White Power rear shocks 13.25 inches long
lift the rear end higher without stressing the UJ too much |
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After running the machine with a Raceco USA two into one featherlight
exhaust from Jim Blomleyís BOTT racer, which was too loud even
for the track, and open bellmouths, I switched to a purpose made
two into two system utilising Supertrapp reverse cone silencers
to my design. The downpipes are 44mm internally to produce mid-range
torque from the 496cc cylinders and are carefully measured to
the same tuned length.
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The Supertrapp silencers allow a degree of tuning for backpressure
due to the baffle plate arrangement at the reverse cone. The headers
are split just beyond the exhaust port using spring connectors to
enable quick dismantling (for things like oil changes) without the
need to disturb the head studs. The split also allows vibration
to dissipate aided by rubber mounted silencers necessary as stainless
doesnít like rigidity. The pipes, bent under the sump to lose length
and drop centre of gravity, means the silencers end either side
of the rear tyre with the consequence that the rear brake torque
arm had to be repositioned above the swing-arm and now acts in compression.
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One of David's inspirations was this V7 Sport racer by Charley
Cole raced in the United States |
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I altered the standard 15 degree carb manifolds by cutting out
a section and rewelding them to 5 degrees as advised by Bruno
Scola to Roy Armstrong for his Avon series winning bike and combined
them with 10 degree, 145mm long K&N air filters from Harley dirt-mile
machines. This straightening of the inlet tract has caused things
to hang out a bit but at least the filters are parallel to the
frame. With a little bit of timing adjustment (including a recurved
distributer to take account of the dual plug heads) and carb tuning
on the dyno the best it could produce at 7,500rpm is 75bhp at
the back wheel. The benchmark specs from a Firestorm show it bettered
that until 8,000rpm where the superior fuel injection of the Honda
took over and the Guzzi ran out of puff. This is using neat high
octane Avgas. I usually run 50% Avgas and 50% Super unleaded."
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