http://www.riveraengineering.com/html/faq.htmlWhat is the difference between the 66 tooth starter ring gear and the 102 tooth starter ring gear and what do you recommend?
In 1994 to present Harley Davidson changed the Big Twin ring gear from 66 teeth to 102 teeth, citing a better ratio for starting as the pinion gear moves the ring gear more efficiently. The problems start when the compression of the engine increases, thus making it much more difficult to turn the ring gear. The added pressure results in the narrower tooth on the 102 to fracture. The tooth on the 66 tooth ring gear is substantially wider and less prone to breakage. Rivera recommends the 66 tooth ring gear in all high compression applications.
http://hdforums.com/m_142104/tm.htmIt's a nice day so you jump on your 2000 FXST motorcycle to go for a ride. You've had a hard week and you know that a good long ride on your Harley will take all that stress away. You hit the starter button and hear an all too familiar sound again. The starter makes a grinding noise and you have to thumb it twice to get it to engage. Your stress meter is pegged and you're thinking of the money you are going to spend on another starter. What the heck is going on here? Are you causing the problem? Well don't feel lonely, as you are not alone and it is not your fault.
In 1989 Harley Davidson began using gear reduction motorcycle starters with a lot more cranking power than the old Prestolite and Hitachi starters. This new power practically ended starting problems for motorcycles on all but very high compression big inch engines. Along with the new starter there was a new jackshaft and gear ratio for the pinion and ring gear. The pinion was a 9 tooth and the ring gear was a 66 tooth. This is a 7.33:1 gear ratio. So if your starter were spinning at 1,000 RPM the motorcycles engine would be spinning at 136 RPM. This was plenty of cranking power for most applications.
There are some easy things you can do to help reduce the problem and there are products that will eliminate the problem.
1. Make sure your motorcycles battery is fully charged and your battery cables are in good shape and not corroded and the starter circuit is functioning properly. If the cables are old or you have an engine with high cranking compression you should consider upgrading the cables:
2. If you have a high performance engine that has high cranking compression, consider using a starter with increased torque. There are many choices from 1.4kw to over 2.0kw with varying finishes. The increased cranking power will actually lessen the load on the electrical system overall.
3. One of the best solutions is to change the gear ratio back to the pre 1994 7.33 or 66 tooth ring gear, 9-tooth pinion gear. There are kits from Rivera that allows you to convert from any 994 and later 10.2:1 ratio to the earlier ratio. These kits include all needed motorcycle parts and instructions and are easily installed. There are kits for the 94-97-clutch basket and the 98 and later clutch basket.
If you run a 1994 and later primary drive ratio and have trouble lighting up a big inch hot rod engine, revert to the earlier 1989-1993 pinion/ring gear setup. Or, switch to Compu-Fire's 10/84 ring and pinion for an increase in leverage. Why? This gets a little weird, but here goes: Then, HD used a 9 tooth pinion and a 66 toot ring gear, a 7.33:1 ratio. So if your starter was spinning at 1000 rpm, the clutch would be spinning a 136 rpm. Factor the primary drive gearing 1.54:1 into things and through the clutch, the flywheels cranks 209 rpm. In 1994 HD changed the starter gear ratio to 10.2:1 with a 10 tooth pinion and a 102 tooth ring gear cranking the clutch over at 98 rpm. But, the primary ratio changed to 1.44 at the same time, giving a net loss of crank spin for the same 1000 rpm at the starter of roughly 30 percent to 141 rpm.
In 1994, Harley Davidson changed the gear ratio to 10.2:1 or a 10-tooth pinion and a 102-tooth ring gear. The reason is unclear but perhaps the idea was to get cranking power by reducing the RPM. As in our example above, the new and current gear ratio would crank the engine at 98 RPM. In theory, the change in gearing would allow more power to be applied to the task of cranking the engine. Like starting off in first gear versus second gear. The change in gear ratio created another problem though. Since the diameter of the ring gear cannot be changed, adding 36 teeth means one thing - smaller teeth. The same thing applies to the pinion gear.
When the starter is engaged, the pinion gear starts rotating as it pushed out ward to the ring gear. If there is a misalignment between the ring gear and the pinion, the back cut on the ring gear helps engage the pinion gear and ring gear. However, there is always some damage done as the pinion attempts to engage the ring gear. If you get a kick back or the battery is a little weak more damage happens. When enough damage is done the starter makes that grinding sound like a Chevy with a bad ring gear does. It's the same thing really. A misaligned starter on the ring gear of the Chevy causes the pinion gear to not engage properly and it wears the ring gear teeth and you get that familiar grinding noise we all have heard. Kickback is another issue and is caused by cranking compression, improperly set ignition where the spark is not delayed for a few RPM before firing, too much initial spark advance and weak battery voltage of bad cables , etc. These can all contribute to starter problems for your motorcycle but usually this is what causes a starter clutch failure.
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Topic: 110" Starter Noise (Read 13252 times)