The original part number in the parts manual for transmission bearing #31 is 93306-30512. This number was superseded by 10-93306-30517-00. If you use parzilla lookup, it has the part number for bearing #31 as 93390-00012-00 with a #90 as a prefix.
I purchased the original bearing on ebay but am curious about the change in part numbers. Is the new number supposed to be an improved bearing?

I just received the part number 93390-00012 and it is a roller bearing rather than a ball bearing. The dimensions appear the same (as I would fully expect) but there is one other difference that has me perplexed.

On the outside of the outer race there is a small nub about 2mm high and 3mm dia around mid depth. It looks like an index pin to prevent walking. But, it also prevents installation as the bearing pocket does not have a receiving notch for the nub.

I'm suspecting the nub will need to be ground off before I can proceed. Before I proceed I'll see if any forum members have dealt with this issue and how.

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As far as I know, the 93390-00012 bearings were first (and only) used on the crankshafts of the TZ models .... but may have eventually found it's way into other applications. The roller bearings are top of the line stuff . . . designed for extreme loads, and high rpms.

It's my opinion that the other ball bearings (mentioned by ldw72120), are completely adequate for the DT360 countershaft, and upgrading to the special roller bearing is overkill, and furthermore, does not make mechanical nor economical sense.

I'm not sure who (at Partzilla) decided to list this as a replacement bearing for the DT360 transmission, (I seriously doubt that it's Yamaha's idea) ... but I can tell you this . . . that someone is making more profit selling these, while reducing their expensive inventory.

And yes, that nub is for indexing purposes (in the TZ cases) ... to help eliminate the possibility of spinning the outer race.



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Enduronut, thank you for the candid and informative reply.

The bearing is an expensive part. Your suggestion that this "supercede" part choice may not have been a Yamaha corp decision helps explain why it is not a drop-in replacement and requires modification.

I'll carefully check the dimensions before I hack on it to make sure it will fit correctly.

Unfortunately it won't make the bike any faster as it weighs much more than the original!
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I have a concern about using the roller bearing... I'm not sure if it's valid though.

Roller bearings can't take any side loads. The gears are all straight cut on the output shaft so no problem there. (Helical cut gears, like the stock clutch gear, would put a side load on the shaft and can't be used on a shaft supported only with roller bearings.)

With two roller bearings on the output shaft could it be possible that the shift forks might move the whole shaft side-to-side a little? I think you might need one ball bearing on the shaft to take any side loads created by the shift forks sliding the gears side-to-side?


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That's a good point MarkT.

I'm thinking the drive chain may add side loads under certain conditions as well.

I'm going to return the roller and look for the original PN.

Thanks for the thoughtful feedback.

I have found a wrong turn in my search for this transmission output shaft bearing.

And I'm going to blame it on my GPS!

The transmission exploded view for the part I'm referring to shows this as item #31.

The site I was using to identify the part number is the Babbitts OEM parts site. The parts listing shows the original part number (93306-30511-00) struck out and the supersede number as 93390-00012-00. This replacement is the roller bearing with the nub that I received.

The original part (93306-30511-00) seemed elusive until a discovery was made. I went to another long time supplier of these vintage bike parts (Speed and Sport) and searched using their exploded view and parts listing. What I found was they have item 31 listed as 93306-30512-00. :

After some digging on this PN I find that it is superseded by PN 93306-30517-00. I also find that both are still available! And the supersede is NOT a roller bearing but what looks like the same ball bearing as the original PN but with a seal on one side.

So, thanks to the input from MarkT and EnduroNut I will be returning a part that would need modification to fit, would likely cause other problems (like drive shaft lateral movement) and that cost 3- 4 times more.

I’m about to start on a rebuild of my ‘74 DT360A, and I wide-eyed that $123 part! So am I reading correctly that PN 93306-30517-00 is the one I need to order? Thankfully it’s MUCH cheaper!

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