Vintage Dirt Bike Q & A

Hi I was wondering if anyone could tell me all the years and model applications for the 43mm Showa disc brake front ends for 84 and up CR's? Also how about a list on which 83 and earlier drum brake bikes would be a candidate for a direct bolt on swap without screwing up length geometry? I know these came on 84-?? CR500's but Im not sure about 250's etc. The Showa P/N (sticker) is KA5-742.

There's lots of opportunity here depending on a few variables. It would appear that - because of a common bearing set - triple clamps are inter-changeable from 1979 through 1987 at least. (1987 43mm Showas are considered the dogs testicles.) In some cases there are differences in the length of the steerer but this can be swapped old for new or a spacer used. You'll find many that have put 1981 41mm and 1982-1983 43mm Showa forks on their older 1978-1980 CR250Rs. The brake issue is more challenging. Using post-1984 forks means you want to use a disk on a pre-1983 bike and/or you are willing to fabricate a mechanism to hold the older drum brake. Have seen 1987 43mm Showas on a 1983 CR480R like that. I have only heard of one actually fabricating a lug directly on the fork leg. If you have a set of forks set up for a drum brake, swapping brakes and hubs between years is a snap providing you check the axle you use makes the wheel line up correctly between the forks. Geometry-wise - given you can play with fork height in the clamps and/or shock sag - I would not given a second thought in pursuit of better suspension and braking.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Well what I have is a complete 43mm disc brake front end actually installed on an 83 CR480. Triples, forks, brakes, wheel etc. I guess what I want to know now is what bike and year it could have come off of. The disc brake CR stuff started in 84 and that steering head bearing setup would have ran until? So I have a? Is there a way to tell? The number listed above is what is on the fork legs.

51400 (right fork leg) or 51500 (left fork leg) - KA5 (1984 CR500R) - 742. The parts fiche strongly indicates the same parts were used on the 1985 model. New forks were introduced for 1986-1988, but that does not rule out using the same fork leg on these later models - with new internals. 1989 was the first year of the upside-down forks.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

Very cool, I really appreciate you looking that up!