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Close Ratio XR100 gearbox

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I just got my 150cc motor done (9mm stroker crank and 120cc BBK)and I thought I would try to put it in a XR80 cases to get a close ratio gearbox but the crank bearings are 2mm smaller (on the 80) so i put the XR80 1st thru 4th gear and a XR100 5th gear in the 100 cases so now it has a close ratio 1st and 2nd gear same 3rd and 4th gear and the shorter 5th (XR100 gears) in it.

Just thought I would let you guys know that it works well.

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Good info Phil!!!

And I just happen to have a basket case XR80 engine in the garage somewhere. Yea, no more granny gear for first!

Robert :cry:

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Phil Thats great news. Its one we have often thought about (and tried but never too seriously as its always a rush to get the motor back together to race). Im going to give it a try and also use a XR80 kick shaft to reduce the shaft length.

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Wow, that's wierd Phil. I remember once, that I had a bunch of tranny's in a box (xr80 and xr100), so when I blew my tranny I just grabbed the first one I could find. Anyway, after trying to fit an xr80 tranny into a xr100, I remember the shafts being a different size and I couldn't get it to work.

So did you put the xr80 gears (counter and main shafts on to the xr100 shafts? What about the first gear that's already on the main shaft? And the cases fit back together nicley? I also, remember I got it to work, but the cases would fit right, they were just barely off. Now the kicker: after that, I sold all my xr80 tranny and motor stuff on ebay for less than a dollar a pound. About fifty bucks for about 80lbs of parts. And the guy complained about the shipping costs. Luckily, I guess I can pick more parts on ebay and try it.

Thanks Phil!!!!! :cry:

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the shafts that I used (1992 XR80) where the same length as the XR100 shafts I used (1996 XR100). I just swapped the 5th gear over (actually only one of the 5th gears because the other is the same (24T).I used XR100 shift forks and Drum.

Socal I remember seeing that on e-bay and almost thought of bidding on it.

Also does DMC still have those 59mm pistons?

ACS I didn't notice the kick shaft difference in length. Where are they shorter?

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I thought the diameter is different?

I don't know if DMC has any in stock, but he can make them in a few days. You do need to machine the cases though.

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The diameters and lengths of the shafts are the same. I have an old XL80 tranny and it is shorter and none of it will work. Not sure about what the XR75 4spds are like.

I already have a 58mm Powroll piston kit (cases are already machined) in it now and the sleeve looks thick enough to go another 1mm.

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Darn, I am pretty sure my basket 80 is old. What years XR80 donor should I be looking for, with the plan to install the gears in an '02 XR100?

Robert :cry:

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I'm not sure what years are what size or even if they are different. I know the XL80 (4spd probably the XR75 too) tranny is different.

The one I used was from a 1992 XR80 into the '96 (must be the same as an '02) XR100.

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The kick starter shaft is shorter, it doesnt hang out as far out of the cases and I'm pretty sure it should fit as the gear etc is the same. I want a shorter shaft to give more boot clearence on the CR/XR.

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but who uses first gear not sure if this is the greatest idea if you are only getting second gear C/R i know i like the way i got to the first turn on the 80 though.

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