Lightweights'.

The OW17 has a newly designed engine and chassis; witch shows a shortened engine of the YZ635. Whereas at the rear end is missing a piece, namely the part in witch the rev counter-drive was housed. The crankcases are magnesium ones, just like the brake drums. The engines have a bore and stroke 56x54mm of, and are feed on 34mm Mikuni carburettors. The rev counter-drive is placed to an extra transmission at the water pump. The power is given as 60 hp at 12.000rpm. The rear shocks are aluminium samples, like the brake-pedal. The chrome-molybdenum steel frame is changed to adapt the shorter engine, so that the swing-arm is placed direct against the gearbox, what makes the movement of the chain better. Because the frame is shortened, the swing-arm could be lengthened; witch is giving the machine a better spread of weight. The weight of the machine is only 90kg.. All in all they are lightweight bikes, witch on several places been different on the TZ-production racers and the YZ635 of the previous season.

The pictures shows how very compact the engine is built, with the swing-arm directly against the shortened engine. Also is visible how the revcounter drive is placed on the water pump. The cylinders and heads are external the same as the 500cc OW20 engine, however without the reed valve intake, the shape and direction of the exhaust shows it right.  At the start of the season there are some experimental changes on the exhausts, what is been visible at the curve in the expansions, witch from Hockenheim no more run through the fairing. It's clear this is a "special", which means they were still experimental. And it demonstrates that the development was placed mostly on saving weight and frame-geometry on the bike. The machine above is the 250 OW17 from Jarno Saarinen at the first GP of the season at Paul Ricard, where the both Yamaha's scored at once a 1-2 victory.

The pictured machine concerns the 350cc OW16 from Teuvo Lansivuori, prepared by factory-mechanic Vince French, who did the 350cc machines, such as Ferry Brouwer take care of the 250cc OW17 from Saarinen.

This machine was put into action for the first time at Assen TT that year by Teuvo Lansivuori. The OW16 had a bore and stroke of 64x54mm and pulls out 68 hp at 11.00rpm. His weight is 96kg. This is 6kg more than the 250 OW17 what could mean that this machine is equipped with a normal steel frame because of the extra power from the 350 engine.

Powerfull start of a turbulent season

The GP-season starts at the French circuit Paul Ricard on 22 April 1973. THE subject of discussion was the first outing of the brand-new Yamaha 500 Factory racer. Everybody was looking forward if the four cylinder two stroke could prove his promises.  Obvious the MV-Agusta team was rather impressed by the specifications of this new weapon. The MV factory had declared by a press report not be able to race under the Factory flag in the1973 world championship. The contracted riders Agostini, Read and Pagani have to ride the bikes of the previous year. They would be full supported by the factory. The cloak of this Italian fear was a strike in the metal business witch the MV factories were stricken, and thus not be able to produce new engines for the racers.

But we will keep our attention on the achievement of Jarno Saarinen and Hideo Kanaya on the 250 OW17.

Paul Ricard By the start of the 250 race it was clear; the Yamaha people's ambitions are to be taken serious. Saarinen leads the race from start to finish, and have finally a lead by half a minute to his team-mate Kanaya. Behind the both Yamaha's Renzo Pasolini ended at 3rd place on 6 seconds from the Japanese. It was clear that the new air-cooled H-D twostrokes did not to be match for the Yamaha's. The other places were to be heavily achieved by Michel Rougerie (4), Teuvo Lansivuori (5), Roberto Gallina (6), and Chas Mortimer (7), all on Yamaha TD3 production racers.

Salzburgring  At the Grand Prix of Austria on the 6th of May, Kanaya rushed out from the start, to be at the lead for three rounds, before Jarno catch him up. Jarno overtakes him and builds a lead of 13 seconds at the Japanese.   How extremely fast the factory machines turn out to be, is the fact that they, despite the rain, lapped the whole field.   Renzo Pasolini becomes a wet ignition and drops out lying on 4th place behind Chas Mortimer. Fourth placed was Lansivuori before Dodds and Gallina.

Hockenheim The German GP at the “Motodrome Hockenheim” on the 13th of May give a tremendous battle between the both Finnish matadors’ Saarinen and Lansivuori, witch they were rumbling over the circuit. Kanaya who had a bad start, sees one’s chance to join the leading Finns, and overtakes them in the 3rd lap. What was following is a breathtaking battle between the 3 leaders, witch constantly changed from position. Till Jarno had enough of the play and leaved them at the place, not to be followed by anyone. At the finish he had a 20 seconds lead on Kanaya and more than 30 seconds on Lansivuori. Dieter Braun takes 4th place before Jansson and Grassetti.

Monza  What should to be a beautiful race day, on the 20th of May 1973 at the Italian Monza circuit, becomes to one of the most dramatic days in motorcycle history. Right after the start in the 250 race there becomes an infamous crash, which resulted in the deaths of Jarno Saarinen and Renzo Pasolini. This fatal crash brings out an enormous chaos on’ and near the circuit. By failure of the racing direction and stewards the assistance at the fallen riders started very slowly. Sadly there has no assistance possible for Saarinen and Pasolini…………… About the cause of the accident there have been many doubts about for a long time. The right facts of the matter should be make public years after the accident, namely that the Harley-Davidson of Renzo Pasolini had been seized, and by that caused him to fall, with tragically results. About the accident are written many things, and there are many theories’s passed, but the fact is that the Italian Commission of investigation has tried to conceal the case on the ‘Italian way’, while the truth was well-known by them for a long time…………………

After the deeply regreted accident the Yamaha team went back home to Japan, including the bikes, and at respect to the loss of Jarno they windrow officially from the 250 and 500cc class.

Andersson and Mortimer, whom acted more or less as private riders with factory bikes are staying.

Teuvo Lansivuori, close friend of Jarno was thrown in at the deep end, barely recovered from the shock.

He wants to stop racing, but the team brings him change his mind, he has at that moment chances to win the 250 and 350 world title.

Teuvo wins with the 250 at Belgium and Finland, and becomes 3^rd in Tsjecho-Slowakia. With the 350 he wins in Tsjecho-Slowakia and Sweden, and is 3^rd in Assen after a breathtaking duel with Agostini and Read. He takes in his famous style the lead over both MV’s, but he must to let the MV’s go in the 13^th lap because of gearbox trouble.

The ultra lightweight engines were being very fragile by all these extreme weight-saving changes and because of the extra power, in particular the cranks are fragile and they are cracking soon, so that Ferry Brouwer, Teuvo’s 250cc mechanic at that moment must refresh them regular. Also the magnesium crankcases cracking near the crankshaft, by heavy vibrations of the engine. The bikes gave not the success they had hoped for.

Teuvo Lansivuori becomes no world champion in that broken season; he ended in both classes 2^nd in the final score of the world championship.  In the 250 class after Dieter Braun on a TD3, and later a TZ250. And in the 350 class he ended after Giacomo Agostini on the MV-Agusta.

At the end of the season Teuvo raced also the 500cc four cylinder OW20 in some matches in England under the same Arwidson flag. By his first appearance at the famous “Race of the Year”, he must get used to the power of the bike, and he is crashing the bike in such a way, he could not even start with it at the race anymore. Luckily it has no consequences to his employment with Yamaha, because he gets a factory contract for his solid appearance that year.

Technical specifications 250 Yamaha OW17

• New shortened engine with magnesium carters
• Lightweight crankshaft.
• Bore and stroke 56 x 50 mm.
• 34mm Mikuni carburetors.
• CDI ignition.
• 6 gears.
• Chrome-molybdenum steel frame.
• Aluminium schocks en brakepedal.
• Magnesium drumbrakes.
• Power (about) 60 hp at 12.000 rpm.
• Weight 90 kg.

The 350 OW16 which was flown over from Japan to the Duch TT of Assen is a 350 engine in the lightweight chassis from the 250 cc OW17.

Technical specifications 350 Yamaha OW16.

• Bore and stroke 64 x 54 mm.
• 34mm Mikuni carburetors.
• Power (about) 68 hp at 11.000 rpm.
• Weight 96 kg.