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Difference between revisions of "Yamaha TZ250"
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==The TZ250== | ==The TZ250== | ||
At the start of 1972, [[Yamaha]] Factory mechanic Ferry Brouwer fitted a pre-production watercooled top end set-up to "Brit" Chas Mortimer's TD3. The paddock was buzzing with excitement at this revelation and by the time the GP season had kicked off, several other leading riders had appeared with the same equipment. | At the start of 1972, [[Yamaha]] Factory mechanic Ferry Brouwer fitted a pre-production watercooled top end set-up to "Brit" Chas Mortimer's [[Yamaha TD3|TD3]]. The paddock was buzzing with excitement at this revelation and by the time the GP season had kicked off, several other leading riders had appeared with the same equipment. | ||
==TZ250A== | ==TZ250A== | ||
[[Image:1973-Yamaha-TZ250A.jpg|right|thumb|1973 Yamaha TZ250A]] | [[Image:1973-Yamaha-TZ250A.jpg|right|thumb|1973 Yamaha TZ250A]] | ||
The TZ250A came out in June 1973 and, like the 350, was virtually unchanged porting wise from the previous aircooled racer apart from a slight widening of the main transfers, also, the exhausts were unchanged. | The '''TZ250A''' came out in June 1973 and, like the 350, was virtually unchanged porting wise from the previous aircooled racer apart from a slight widening of the main transfers, also, the exhausts were unchanged. | ||
Unlike the TZ350, Yamaha chose to have built-in automatically variable ignition advance in it's Hitachi TIA02-16 CDI unit. It was programmed to advance linearly from the initial mark alignment static to a maximum advance of typically 14 degrees at 3000rpm. It then returned slowly and linearly as the revs increased, reaching the original alignment set point again at 10,000 rpm. Beyond 10,000 rpm it continued to | Unlike the [[Yamaha TZ350|TZ350]], Yamaha chose to have built-in automatically variable ignition advance in it's Hitachi TIA02-16 CDI unit. It was programmed to advance linearly from the initial mark alignment static to a maximum advance of typically 14 degrees at 3000rpm. It then returned slowly and linearly as the revs increased, reaching the original alignment set point again at 10,000 rpm. Beyond 10,000 rpm it continued to | ||
retard at the same rate at which it approached 10,000 rpm. (i.e. 2 degrees per 1000 rpm) | retard at the same rate at which it approached 10,000 rpm. (i.e. 2 degrees per 1000 rpm) | ||
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==TZ250C== | ==TZ250C== | ||
1976 saw the appearance of the much awaited | 1976 saw the appearance of the much awaited '''TZ250C'''. The biggest news here was the new "Monoshock" chassis, with the rear shock featuring adjustable pre-load and compression damping, as well as disc brakes front and rear. Motor-wise, the factory chose to pursue ease of riding rather than outright horsepower. Revised porting comprising wider intake and transfer ports with altered angles of entry, raised compression and a new exhaust achieved this for them to a certain degree. The exhaust was mounted on new design brackets, and the clutch basket "boss" to primary driven gear attachment was improved by changing from previous model's "dog" teeth to a female spline, this of course required the primary driven gear to be altered to utilise a male spline. The bike sold remarkably well at just £ 1,500 including a well stocked spares kit. | ||
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==TZ250F== | ==TZ250F== | ||
The | The '''TZ250F''' heralded welcome news for Yamaha fans when it was released in 1979. A 11kg weight reduction was achieved through further changes to the frame, (despite the fact they reverted back to welded steel engine mounting brackets from the alloy ones on the "E") including a steeper rake and an alloy swingarm, as well as this the bike featured a new exhaust and mounting system, an additional o-ring (from the previous single o-ring) in the header pipe, new conrod, wider intake port and minor carburettor mods. The primary drive gear picked up 2 teeth to match the 350's 25, the cylinder drain tube was altered. A dipstick was also introduced and the brake calipers became cast alloy units like the 750's . Power remained the same as it had since the "D" at 53bhp @ 10,500rpm. A new fairing adorned the machine which was pointed below the header pipes and eliminated the old aluminium belly pan, a new fuel tank and seat unit appeared, and the clutch cover was reduced in size to a pressed aluminium job (the previous models utilised a cast aluminium unit completely covering the clutch) surrounding just the rear of the clutch unit. | ||
==TZ250G== | ==TZ250G== | ||
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The 1981 "H" represented the factory's first departure from the popular 54mm bore x 54mm stroke (essentially) configuration of the previous 9 years along with a switch to an individual cylinder casting configuration. In an effort to further boost horsepower, the bore was increased to 56mm and stroke reduced to 50.7mm, achieving the full 249cc in the process and mechanical exhaust power valves were fitted, as was a transmission oil pump to deliver the reduced oil capacity of the gearbox to crucial points. The "H" had a 38mm shorter motor than the "G" and 36mm ZC series Mikuni carbs replaced the usual 34mm SC's, which had been in use on the 250's since the TD3 way back in 1972. Intake port was again widened, as were the secondary transfers for the second year running. | The 1981 "H" represented the factory's first departure from the popular 54mm bore x 54mm stroke (essentially) configuration of the previous 9 years along with a switch to an individual cylinder casting configuration. In an effort to further boost horsepower, the bore was increased to 56mm and stroke reduced to 50.7mm, achieving the full 249cc in the process and mechanical exhaust power valves were fitted, as was a transmission oil pump to deliver the reduced oil capacity of the gearbox to crucial points. The "H" had a 38mm shorter motor than the "G" and 36mm ZC series Mikuni carbs replaced the usual 34mm SC's, which had been in use on the 250's since the TD3 way back in 1972. Intake port was again widened, as were the secondary transfers for the second year running. | ||
The motor spun in reverse direction as the factory tried to further reduce the stress on the rear of the pistons. The crank was no longer a single unit, it was now a pair of cranks with a gear on the end to deliver the power to the gearbox. Despite the frame shedding 3kg, the overall weight was reduced by just 1kg. The steering rake was altered and the swingarm also lengthened to compensate for the shorter frame length of this model. The engine was now mounted slightly further towards the front of the bike. The new rear shock became fully adjustable for both compression and rebound damping as well as pre-load and the shock picked up a rear rubber mounting. The fork diameter went up by 1mm and brake wise the factory reverted back to the old cast iron calipers which didn't bend under pressure and also didn't fade when hot. The new ignition dropped an igniter and pulser coil, there was now just one of each and the inner clutch hub now became a single piece unit to eliminate one reliability problem from previous years. The un-necessary neutral switch mounting disappeared | |||
==TZ250J== | ==TZ250J== | ||