FASTER FIRE ENGINE A new/old MV Agusta 750 F4 special

ENGINE FIRE FASTER

A new/old MV Agusta 750 F4 special

Words & Photos by Robert Smith

It may have bia. The affair blosbeen the bang somed and soon the on the head. Canada kids arrived: a 1958 Or meeting MV 125 Tourismo Italian racing legend Rapido Extra Lusso and an Giacomo Agostini. Or the old MV Chicco scooter. The little photo of a Magni MV pinned TREL secured second-in-class to the wall of his shop. Or at the prestigious 2008 Legall three. Whatever spurred end of the Motorcycle show Canadian Jim Bush to build a in Half Moon Bay, Califorreplica Magni Agusta with a nia, at which Agostini was a modern 750cc MV F4 engine judge. The great man, 13-time doesn’t matter: the result is a Grand Prix champion on the spectacular blending of trared Agusta “fire engines,” was ditional styling and modern kind enough to sign the baby functionality. MV’s gas tank.

The bang on the head came While the Brutale became when Bush high-sided his Bush’s go-to street ride, his BMW R1200R on tour in New preference was for more Zealand, leaving him with power. An eBay search four broken ribs and a mild turned up a 910 engine from concussion. The bang may a crashed later-model Brutale, have freed up a few neurons, which was quickly installed because his dream bike startin Bush’s own bike, leaving ed to take shape soon afterthe 750 F4 engine without a ward. The idea was in place home. That created a kind of but it still needed a deadline; cognitive dissonance in the that came in the form of an Bush brain – a motorcycle invitation to show a bike at engine sitting on the floor the Quail Motorcycle Gatherwithout being fitted in a rolling in Carmel, California in ing chassis seemed somehow May of 2012. Just Wrong.

If the Quail Gathering was With the Magni photo on the incentive, the opportuthe shop wall for inspiration, nity came earlier from eBay, Bush set to. Arturo Magni and at the bottom of it all joined MV Agusta in 1950 was a love affair. It was at as a mechanic and would the Seattle Motorcycle Show retire in 1976 as race director, in 2004 that Bush fell for an spanning a time that saw the MV Agusta F4 750 Brutale, small Italian company win the resurrected brand’s naked some 3000 individual races inline-four. Within a week or and take home an amazing 75 so, one was in his garage in world titles. He and his sons White Rock, British Columthen set up a speed shop con

nThis is what happens during long Canadian winters when you have a heated, well-stocked garage, aboveaverage fabrication skills and a fascination with sexy red Italian four-cylinders. Here builder Jim Bush is in the final mockup stages. Modern MV four looks at home amidst classically styled café chassis.

verting Agusta streetbikes into Magni MV race replicas. Over the years Hondas, BMWs, Moto Guzzis and Suzukis would also get the Magni treatment.

Why not a modern Magni MV, reasoned Bush? But first he needed to design a frame around the F4 engine’s mounting points. For this, Bush credits input from Michael Moore of EuroSpares (www.eurospares.com) in California. Chassis guru Tony Foale’s book Motorcycle Handling and Chassis Design: The Art & Science was also a useful resource.

First job was to anchor the engine in a custom jig to hold it rigidly in place. Bush chose 1-inch mild steel with 0.063-inch wall thickness as the frame material. In researching 4130 chromoly tubing, Bush concluded there was no real advantage in the lightweight chro-mo – weight was not a major issue, and 4130 can become brittle with welding, leading to breakages. Not good. Next, Bush had to teach himself TIG welding, which he’d concluded was the method best suited for strong joints with minimum effect on surrounding areas.

Main frame tubes were persuaded into shape with a mandrel bender and tack-welded into place. With some adjustments, brackets and gussets, the main elements were in place, including the steering head, to which would be fitted modern Triumph Daytona tripletrees and fully adjustable 45mm Showa forks. Bush attacked the forks with a zip-saw to remove the caliper brackets (surplus to requirements, as he planned to use a periodlooking drum brake), then chucked the legs up in his lathe and turned off any surplus metal to replicate old-style Cerianis. Next came new billet fender mounts, glued into place to avoid any issues with welding distortion.

The swingarm, fabricated from rectangular-section steel tubing, went through three iterations before Bush was happy with the strength, weight and rigidity of the triangulated-andgusseted piece. Next came paint. Bush used Endura two-pack polyurethane GM Super Red 71U in his lighted, heated and well-ventilated paint booth.

Frame painted, now the tripleclamps could be installed and the Daytona forks fitted. At the rear, Bush chose Works Performance shocks, which the company kindly customized for him in old-school body-down format. Wheels were built up using a new Grimeca four-leading-shoe drum at the front and a Ducati drum from a 750 GT at the rear. The hubs were laced to WM2 and WM5 18-inch Morad alloy rims using spokes from Buchanan, and fitted with Bridgestone BT45 tires in 140-section rear and 100-section front sizes. A new sprocket carrier machined from billet completed the chassis parts, and a front fender was borrowed from a 1995 Triumph Thunderbird.

Gas tank and mufflers were sourced from Arturo’s son Giovanni Magni

in Italy – though they had to be extensively reworked. The 1974 MV America tank bottom was cut out and reworked to accept the F4’s electric fuel pump, and the front needed reshaping to fit around the steering head. It took some confidence (and more than a little apprehension) to start cutting up a $1000 gas tank! Bush made his own seat pan from fiberglass and upholstered it, then water-jetted his own MV logos from stainless sheet and polished them to use as trim for the pipes.

The F4 engine’s fuel-injection system required some modification to fit. The stock Brutale has an airbox where the gas tank should be, with the throttle bodies angled upward. There was no room for this arrangement on the special, so Bush sourced 2-inch aluminum elbows and modified them to turn the throttle bodies horizontal. The intakes use screened velocity stacks.

The fairing is another Magni item, which houses a period Aprilia headlight and CEV turnsignals. Bush made his own MDF plugs to lay up the fiberglass for the Magni-style sidepanels. Adjustable clip-on handlebars from Apex are fitted with Brutale switchgear, and pretty much all the rest of the electrics are transferred from a donor F4. That means the digital dash was retained, and while Bush would have preferred traditional analog instruments, the cost and time involved in reworking the Brutale electrics didn’t seem worthwhile.

Bush points to the many, many hours he spent making up brackets, lugs and all the other miscellany needed to fit and finish the MV’s componentry. He’s especially proud of the omni-directional ball-mount compensator he designed and made for the front brake cables: The brake lever would normally actuate both sides of the 4LS drum via a splitter, needing constant adjustment for perfect balance; Bush’s ball unit is selfcompensating. Also worthy of note is the hidden hydraulic clutch. The bar lever pulls a cable connected to a master cylinder under the gas tank, allowing Bush to keep the period handlebar profile.

The finished machine is a people magnet when parked and literally a head-turner on the road. A flash of red and silver and the four black pipes cause drivers to give chase to find out what it is – usually they’re still baffled. And the sound of the F4 motor breathing through open stacks and blowing out of Magni pipes is hard to describe. Imagine a chainsaw shredding a trumpet full of angry hornets!

Bush now has over 5000 miles on his MV special, and reports very few issues. The gearshift linkage needed to be redesigned and a dyno test revealed that quite a few ponies had gone AWOL from the motor, at least partially the result of losing the airbox and tuned exhaust. Bush has plans to relocate the fuel injectors, which, with more re-mapping should help attain his goal of 100 hp at the rear wheel. Overall, though, Bush is delighted with the result. Not that he wants to see another one like it any time soon so, please, don’t even ask.

“No, it’s not for sale,” he affirms. “Nor will I build you a frame…” nGiacomo Agostini joined the MV Agusta team in 1964. He parlayed moviestar good looks and immense riding talent into 122 GP wins and 15 world titles – 13 for MV, his last two for Yamaha in 1974- 75. “Ago” also went to victory lane 10 times at the Isle of Man.