Generations -- what's all this Gen I, Gen II stuff I see?
Generations refer to the revision or iteration number of an object or system.
- Rockers come in three generations or variants.
- Generation 0
- Generation I
- Generation II
were those installed in new XV750s and 920s at the factory during the first two model years. They were improperly hardened (along with the cam lobes) and there was a general recall. Most were replaced before the bikes went on the showroom floor. For those that were already sold, Yamaha sent letters to the registered owners, and presumably those owners had the defective parts swapped-out at the bike's first service. This arrangement worked as long as the engine was never stressed hard, and kept awash in plenty of clean oil. These sometimes still show up; not every owner took the letters seriously.
had hardened surfaces, but not very deep. The bikes could be red-lined without self-destructing. Still very sensitive to oil quality and quantity, these can be detected by the oil hole dead center of the pad that meets the cam lobe. Era not clear: possibly just the replacement rockers from the recall.
were characterized by prominent pads of hardened steel where they met the cam lobe. The oil hole was no longer on the pad. It now was located above the pad, presumably for more even coating.
- Generation 0
- Starter Gear Assemblies -- or "throw-outs."
- Gen I
- Gen IIa
- Gen IIb
- Gen IIc
- Gen IIIa
- Gen IIIb
Used '81-'83 on the 750 and 920. Very noisy at best; subject to many after-market "fixes." The starter motor spun, turning a series of gears that ultimately slammed a drive gear into the teeth of the rotor.
Used '84, '85 on 1000s (TR1 -- from '81 on -- as well as Virago). Used an automotive-style solenoid and bendix, which in turn opened a scissor-like mechanism to push a drive gear into engagement with the rotor teeth. Quickly superceded to Gen IIb.
Used '86 -'90 on 700, 750, 1000, and 1100. Improved bendix to cope with back fires, more robust gears.
Used '91 - '98 on 1100. Not really new, just some adjustments in part sizes and depth of engagement.
Used '99-'09 on XVS1100. Used a roller clutch scheme to spin up rotor; disengage when engine started. Parts supersede to those of Gen IIIb. More robust solutions may be available in the after market.
Used on the XVS1100. A supersession on Yamaha's part; a refinement only. It overcame some wear problems, and was better able to cope with the occasional back-fire. Did not come stock on ANY bikes; it was implemented after production ceased.
- Cams Came in several flavors:
- Gen 0
- Gen I
- Gen II
- Gen III
- Cam Variants
were used on '81-'82 750s and 920s. They were involved in the recall mentioned under Rockers, and are presumably all off the road.
stock cam on 750s and 920s through '82. Their lift: .401"; duration: 245 intake, 247 exhaust.
Information lower in the list is suspect. Check "microfiche" sites and our cam page for more depth.
used on some '83 920s, all 1000s, and 1100s. Lift: .391"; duration: 235 degrees. These were intended to enhance the low-end power of the larger bikes.
used on XVS1100s. Specs forthcoming. Note that Yamaha decided that a single spring per valve was adequate for this cam.
are described to an extent in Yamaha service manuals. Yamaha claims different lift and duration specs for the 700 and the 1000, possibly others. Due to the extreme durations claimed, we believe that Yamaha reckons duration at zero lash plus ANY lift at all -- which would include the acceleration ramps. Cam durations from other sources are figured at .040" lift.
Some things came in Generations, but we have not yet sorted them: coils, TCI, ignition pickups, rotors and stators.
Some things didn't come in Generations: valves came in two variants: 700 and 750; and everything else.
Valve springs could be said to have two Generations: everything; then the XVS1100.
Cylinder heads had two variants: kidney shaped (700, 750, 920, 1000); and flattened hemisphere (both 1100s).
Left engine covers spanned: '81 - 83; '84 - '85; Midnights; 1100s; then the XVS1100.
Left engine cover gaskets came in two Generations: all '81 through '98; then the XVS1100. Further investigation necessary: photographs suggest that one gasket spanned the series.
Right engine covers went through several variants: '81 - '83; Midnights; 700s and 1000s; 1100s; the XVS.
Right engine cover gaskets followed a simpler pattern: all XV the same; the XVS different. Update coming: it is possible that one gasket encompassed the entire series.