Driving report TM Racing 400 F
Who sows the wind…
…will reap storm. The off-road scene sets the sails in terms of four-stroke technology. Surprisingly far ahead in the bumpy regatta: TM Racing with a new engine.
Raider has long been called Twix, Aktion problem child is now Aktion Mensch and Moto TM is now TM Racing. Why?
But at the moment it’s not just about speed on the slopes, but also in the development departments. Because one thing is certain: the two-stroke engine is dying, and long live those who can supply the new market with light four-stroke off-roaders. Because although Yamaha showed the flag with the YZ 400 F in 1998, most of the manufacturers (see box on page ???) are still forging their weapons.
Chief engineer Eduardo Rossi knows what everyone is thinking: “Our engine is not a Yamaha copy,” assures the 43-year-old. In fact, the TM unit suggests a kinship with the Japanese pacemaker, especially through the voluminous double cam head. Understandable, because if you are looking for performance in the relatively small displacement range, you have to ensure sufficient revving. However, high engine speeds that increase performance can only be achieved using a rigid valve train with two camshafts. Because a short stroke is also an advantage, TM Racing also adopted the bore-stroke ratio of the Yamaha: 92 by 60.1 millimeters.
The most obvious difference is the double loop frame, which has long been typical for TM Racing, which enables a different carburetor arrangement. Contrary to all previous solutions in the off-road sector, the fresh gas finds its way via the inlet, which is inclined at an angle of 45 degrees to the cylinder axis, which is favorable for flow. The carburetor – a 40 mm Mikuni flat slide valve with a horizontal float chamber instead of the Keihin FCR gas factory that is omnipresent in sport-oriented four-stroke circles – can easily be found in the space between the frame tubes. Only: To do this, the fresh air from the air filter conventionally placed behind the engine now has to hit two sharp hooks in the direction of the carburetor.
The framework concept creates even more freedom. Because the engine can be placed higher for sufficient ground clearance. The advantage: Signore Rossi is therefore not dependent on the absolute minimization of the overall height and brings the 1.6 liters of engine oil – without using the frame as an additional oil reservoir – completely in the engine housing. The unwanted panch losses of the conceptions with the oil sump under the crankshaft are countered by a false bottom. A partition separates the engine oil from the rotating shafts, and two oil pumps supply the lubricant. Incidentally, the five-speed transmission including the hydraulically operated clutch comes unchanged from the company’s two-stroke models.
As is the case for the other displacement variants. A 250 motor – albeit with the same stroke as the 400 – and a 530 model with the same housing are planned for the coming year. If everything goes according to plan, the second development stage should also be in place by then. The mounts for the electric starter and the sensors of the Marelli-Weber injection system have already been cast into the housing.
Which means for the moment: We’re still kicking, with our virginal TM 400 F with engine number 006. Choke pulled, two or three kicks, and it purrs. Not too loud and practically without vibrations, although Master Rossi, unlike Yamaha, did without a balance shaft. The first straight. How was that? Short stroke? Two camshafts? Yamaha? Right. And the TM turns up just as with relish. The TM does not know the rev limiter that stalls the Yamaha unit at 12600 rpm. The four-stroke cheers in the highest tones. That’s why things are moving quickly. It should. Almost 50 hp? are the usual standard in the 400 league in sport enduro. This is also how much the TM subjectively achieves.
The blue one can only be switched through unwillingly. It still happens when the machining burrs on the gearshift mechanism have worn off, says Mike from Mike’s Bike Shop, the German TM-Racing importer. Let’s hope with him. And also that the Mikuni, which is tuned too lean in the lower speed range, fills the hole when accelerating out of tight turns. Because what inspires in spite of this naughtiness, are precisely the properties that the 400cc four-stroke engine have now put in the hearts of an entire generation: plenty of traction. Hard turns with loose clods of earth – no problem. The TM pushes forward with perfectly controllable drifts. No thought of a rough rear wheel erupting. Stay cool despite a hot tire.
Which also works on bumpy slopes. The tuning of the Öhlins shock absorber is almost perfect, the upside-down fork from Paioli is – typical for enduro bikes – on the comfortable side. The rigid frame from our own production is not impressive anyway. In general, no savings are made with TM. Lovingly self-milled hubs, fork bridges ?, pinions and foot brake levers as well as in-house brake discs including components from Nissin look valuable and give the 400 TM its own character for the fight against the upcoming competition.
D.She also needs it, because the air will soon be thinner in the tunnel business. And it’s always good to be a little earlier.
Technical data – TM Racing 400 F
Engine: Water-cooled single-cylinder four-stroke engine, two overhead, chain-driven camshafts, four valves, wet sump lubrication, Mikuni flat slide carburetor, O 40 mm, kick starter, oil content 1.6 liters. Bore x stroke 92 x 60.1 mm, displacement 399.3 cm3 Nominal power naPower transmissionPrimary drive via gears, hydraulically operated clutch, five-speed gearbox, secondary drive via chain. ChassisBridge frame made of oval steel tubes, bolted rear frame, swing arm made of aluminum box profiles, central spring strut, adjustable spring base, rebound and compression damping, upside-down fork, O 46 mm, adjustable Rebound and compression damping, disc brake with floating double-piston brake caliper at the front, O 270 mm, disc brake with floating single-piston brake caliper at the rear, O 220 mm. Spoked wheels with aluminum lining, 1.60 x 21, 2.00 x 18; Tires 90 / 90-21, 140 / 80-18. Chassis data, wheelbase 1490 mm, steering head angle n.a., spring travel f / h 300/300 mm. Color blue Price 14,990 marks VAT and additional costsImporteurMike’s Bike Shop, Ruppen 8, 96317 Kronach, Telephone 09261/61576.
Something is happening in the off-road business. Since Yamaha demonstrated the decisive advantages of uncompromisingly designed, low-displacement, high-revving four-stroke machines with the YZ 400 F three years ago and KTM followed suit with the 400/520 Racing, the rest of the competition has been in the starting blocks. After starting difficulties this season, Cannondale finally wants to bring the EX 400 with an aluminum frame and 400 cm3 dohc engine with injection and a cylinder head rotated by 180 degrees onto the market. Gas Gas has also been working on its four-stroke engine for a long time. In the coming year, the Spanish 250/400 engine with double cam head will finally power a production bike. The new four-stroke Honda launched its first launch last year. The production version of the 450 cm3 single with only one camshaft in the aluminum bridge frame typical of Honda is planned for 2002. MOTORRAD was able to do a few laps on the 250/400 cm3 four-stroke with double cam head from Husqvarna at the end of last year. In 2002 everyone can have it. A year later, the new, high-capacity bolide from the Italians is to appear with a capacity of around 550 cm3, but with a camshaft. The Italian luxury forge Vertemati is currently about to complete a small series. The single with a displacement of 512 cm3 and a camshaft demonstrates unconventional engine design.
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