1979 Yamaha YZ400 Primary Gear

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2/26/2020 12:58 PM

Does anyone know what the "B" etched on this primary gear means? I have seen A,B,C and D etched on these gears, but I don't know what it is for. I have seen about 20 of these same gears and all of them have a letter etched on them. Photo

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2/28/2020 1:00 AM

Get in touch with Dave Osterman via Instagram. He might be able to tell you. His handle there is @ozzydaveo

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2/28/2020 5:18 AM

Thanks harescrambled!

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2/28/2020 6:39 AM

Just a hunch, but spiral cut gears have a very narrow tolerance for pitch-line allignment. I wonder if the primary gear and clutch basket were manufactured as a "matched" set i.e. like yamaha piston to cylinder tolerances A,B,C,D etc. Just a guess.

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2/28/2020 6:56 AM
Edited Date/Time: 2/28/2020 6:57 AM

DynoDan22 wrote:

Just a hunch, but spiral cut gears have a very narrow tolerance for pitch-line allignment. I wonder if the primary gear and clutch basket were manufactured as a "matched" set i.e. like yamaha piston to cylinder tolerances A,B,C,D etc. Just a guess.

My first thought was the bore of the gear and the end of the crankshaft being a matched set, but that sounds reasonable.

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2/28/2020 8:50 AM

I just looked up a YZ400 clutch basket and there appears to be a "B" engraved in the top left of the basket ring gear as seen in the picture below. Not the best picture but it does appear to be an engraved letter at the root of the tooth. Photo

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2/28/2020 9:44 AM

After looking at a few on ebay, I see the same markings as the one in your picture. It looks like you are onto something DynoDan. I will take a look at mine as soon as I have time. Thanks for the help!

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2/28/2020 10:55 AM

Sure! Good luck!

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