A 4th Generation Gearbox?

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A 4th Generation Gearbox?

Post by Go Go Diablo » Sun Aug 12, 2012 7:32 pm

From the "Just when I thought I saw everything" file, today I saw something new regarding Diablos.

In 1967, Bolens made two versions of the gearbox for the 500. In that year, they added more cover screws and upgraded the idler wheel from a plastic roller to an actual gear and they did this sometime during the production year.

Then for the 1968 production year, they totally upgraded the gearbox to what we know of as the gearbox used in all 502's and 503's.

Today, I am cleaning up and rebuilding gearboxes and while I am cleaning one of the aluminum housings, I find a part number casted in the casing. My first thought was "How could I have never seen that before?". But upon further investigation, I realized I have never seen that before. The part number is right above the lower bearing.
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I presume this was a spare part produced by Bolens after the production years of 68' & 69'. Some differences I see are:

- The gussets by the driven shaft are larger and more squared off than the original.
- The housing around the bottom bearing is thicker.
- The casting hole where the brake caliper mounts is smaller giving more material around the mounting area of the sliding caliper mount tubes.
- The upper mount is larger in diameter where it often wears out sliding in the chassis slots.
- The bolt hole pattern around the tensioner is a little different than the original.

Updated on left and original on right.
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Updated on right and original on left.
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Updated on the right and original on the left.
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So now I have to say again, what will I find next? :D

Has anybody else seen this type of gearbox?

Bruce
Too many Diablos and parts to count.
Yamaha 600 SX

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