Yamaha Euro Twin

YAMAHA EURO TWIN

THE SPORTBIKE YAMAHA SHOULD BE BUILDING?

ALAN CATHCART

THERE'S NO QUESTION IT HAS CHARACter. It can compete in the charisma sweepstakes with any bold BMW Boxer, flashy Ducati V-Twin, or gutsy Triumph Triple. It has as much-if not more-personality as these European favorites. "It" is Yamaha's 10-valve parallel-Twin, the only Japanese engine in production that comes close to displaying such a disposition.

Yet until now, you couldn’t find this engine in anything more sporty than the weird-but-wonderful (and discontinued in the U.S.) TDM850. No surprise, then, that the motorcycle world is watching carefully the release of a prototype that could prove to be the Asian answer to Europe’s sport Twins. Built by Japanese frame specialist Over, the bike is making the rounds of the European bike shows, and, yep, at its heart is the TDM850 engine.

Over has dubbed this bike the OV-15A Euro Twin“Euro” because the company is trying hard to beat the rising yen by farming out construction to the English cottage industry. “If we build the chassis in Britain, where I have good contacts, we can bring the cost down quite steeply because of the exchange rate,” says Over boss Kensei Sato. Over is also considering assembling complete OV-15As in Britain so it can escape import taxes when selling the finished bikes to other EC countries. Yet in spite of all these efforts to trim costs, Over has delivered a prototype bike with million-dollar looks and a million-plus-one ride. After sampling the Euro Twin with a sunny day’s ride on British backroads, I defy anyone honestly interested in the fun factor of motorcycling to let go of this bike.

Unique? And how. The Twin is based on last year’s OV-15 racer, a fact made clear the second the throttle is cracked wide open. It’s quite loud. The absence of air cleaners-and a large carbon-fiber silencer that doesn’t stifle as much as you’d expect-lets rip a noise that’s as much track as road. Nice, even if it will have to be toned down for production.

The Over TDM shows its racing roots, too, in its ability to accelerate. By any standard, if s just plain fast, but especially so for a carbureted 850 Twin (actually, it’s 868cc, just like the racebike). One-millimeter-oversize pistons deliver a 90.5 x 67.5mm bore and stroke, and the 12.5:1 compression ratio of the racer drops to 11:1 for the road-still impressive. All the valves in the ported, flowed head are 2mm bigger than standard, which means 20mm inlets (three per cylinder) and two 30mm exhausts, fitted with stock springs easily capable of keeping up with fivefigure engine speeds.

But the single greatest aid in maximizing straight-line performance is the six-speed gearbox crafted out of an OWOl close-ratio cluster, with modified shafts and TDM selectors mated to a specially made shift drum. Actually, the engine doesn’t need that many ratios because it’s very flexible and pumps out bags of power low down, pulling from just over 2000 rpm, practically off idle, and not running out of breath until a shade over 9000 rpm. The motor is turbine-smooth even at high revs because the stock, twin counterbalancers are used, though these do contribute to a porky engine weight of 147 pounds.

The trick is to ride the torque curve in midrange, and revel in the lusty drone from the parallel-Twin motor. The

gearbox scores big-time in the proper choice of ratios it offers. They are so close together you can really keep the engine on the boil.

The main problem with the TDM engine in roadracing (and, so it’s rumored, on the street) has been a crankshaft that suffers in stock, dry-sump form from insufficient oil supply, and the main bearing or big-end problems that result. That’s no problem on the Over TDM. It instead has wet-sump lubrication and increased capacity (7 quarts of oil vs. 4.5 quarts on the stock dry-sump system).

Another mark of the improved lubrication available with the new system:

It saves weight, using only one oil pump, rather than the two found on a stock TDM. An Earl’s oil-cooler, matched to a water radiator sourced from a Kawasaki ZXR400, helps keep the temp down. Ignition is a stock CDI, modified to give a different advance curve, with a 12-volt battery under the seat where the oil tank used to live on the racebike.

The frame is modified, as well.

You’ll still find Over’s trademark oval-section aluminum tubes, but the OV-15A uses wider-section tubing that is internally braced with a single longitudinal rib. With a swingarm pivot and rear-engine mount milled out of solid 5087 alloy, you get a very stiff structure. A fully adjustable 43mm Showa upside-down race fork is fitted, combined with a single-sided swingarm specially designed and manufactured for the OV-15A. It’s made up of four pieces of alloy milled from solid, then welded together with a cross bracing at the welding line.

This all makes for great, ultra-stable handling around sweeping turns, yet the bike is light and quick in the tight stuff. The rear suspension is noticeably progressive in response, and the front is just about flawless: Hit a bump at full lean, and the Showa fork shrugs it off. No steering damper is fitted, and none is needed.

The big Brembo cast-iron discs and four-pot Nissin calipers are unbeatable for the street. Expensive, too, and the mega-yen race components may have to be replaced with something a bit more humble for production bikes.

About the only thing worth mentioning in the room-forimprovement-department: The rear brake, lifted from an RC30, and not at all effective.

No complaints about the bike’s looks, though, a big departure from earlier TDM racers, which were a little, er, functional, shall we say, in the style department. But a professional design house in Japan clothed the Euro Twin roadster, and the result is certainly attention-grabbing. The front end looks a bit familiar-somewhat derivative of the Norton F2, especially the way the FZR1000 headlamps beam through a smoked screen that extends down toward the front fender. But the chassis is simply gorgeous, showing off the handsome engine.

Over chief Sato has a strong reputation after the success of his Over Racing SRX Singles, and his TDM racer is developing quite a track record, too. Sato produced a revised version for the 1993 Suzuki 8-Hours, where Shinichiro Ohura and dirt-tracker-turned-roadracer Kevin Atherton succeeded in qualifying in the midst of much faster F-l Fours. Crash damage put them out of the race, but Ohura surprised many by taking the Over TDM against-all-odds to 20th place in a round of the hotly contested Japanese F-l championship. Some Twin!

The question now, of course, is whether Over’s latest street project will enjoy the same success in the marketplace. If it does, the OV-15A may leave Yamaha kicking itself for missing the chance to be first to make an exciting, Euro-style sport Twin out of the TDM. O