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Working on the Disassembled Engine

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Written by Randy Fox   
Saturday, 03 November 2007

Transmission Bearing Tips

 

transmission bearings out, Yamaha Road Star
My 'bad' transmission bearings

Transmission Bearing Tip-1

If your tear-down purposes include replacing transmission bearings, you'll need to buy new ones--duh. Note that the ball bearing assemblies of the transmission are not Yamaha specific. They are standard, industrial, electric-motor bearings. As such, you do not need to pay nearly double the market price for bearings from Yamaha--in my opinion.

Even my Yamaha dealer (owner) said they often use off-the-shelf-bearings from a local bearing distributor. Only the clueless guy in the parts department maintained that I shouldn't chance it by installing anything except 'Yamaha brand.'

Everyone, including my local bearing supplier, did warn me against one thing however: Don't use bearings made in China. So I ended up getting brand new, better-than-OEM-quality, direct replacement bearings at half the cost of buying them through Yamaha.

Here are the industry-standard part numbers from each of my stock (2003) transmission bearings:

  • Left Case
    • For the main axle, the larger, 7-balls bearing:
      • Brand name of my stock one: Koyo
      • Generic bearing part#: 63/28-3
    • For the drive axle, the smaller, 9-balls bearing:
      • Brand name of my stock one: NSK.
      • Generic bearing part#: 6205
  • Right Case
    • For the main axle, the smaller, 7-balls bearing:
      • Brand name of my stock one: Koyo
      • Generic bearing part#: 6304
    • For the drive axle, for the larger, double-track bearing:
      • Brand name of my stock one: NSK
      • Generic bearing part#: 5206

These part numbers specify everything about the bearing: the OD, the ID, the ball tolerances, the steel hardness, the number of balls--everything. The brand name doesn’t matter too much as they are all comparable, although Timkin and NTN are good brands--my bearing distributor said--and are not Chinese. Timkin and NTN are the brands I got.

 

Transmission Bearing Tip-2

I sent my engine for powdercoating before I removed the ball bearings in the cases (not a good idea). My powdercoater asked me if he should proceed, and I said, “Yes.”

When I got my cases back, the bearings were toast. I tried to replace them on my own using an oven, a propane torch, and a dead-blow hammer, but I had no luck. I didn't want to chance ruining the new powdercoating so I took my cases to a decent Yamaha dealer. They tack-welded a brace to the face of both blind-bearings, and easily yanked them out using a bearing puller. See photo below. Then they used a hydraulic bearing press to get the new bearings seated. Moral? Get those bearings out beforehand.

 

transmission bearings removing, Yamaha Road Star

 

Transmission Bearing Tip-3

If you have someone press in your ball bearings for you, be sure to do a test-fit to make sure they are fully seated. I assumed mine were installed properly. When I assembled the crankcases (including Yamabond), I discovered that two transmission bearings were not pressed in fully. I had to disassemble everything, have the bearings re-pressed, and start all over. It cost me over a week.

 

Transmission Bearing Tip-4

The drive axle has an oil seal. It goes into the rear of the right-side crankcase. This rubber seal separates the engine oil from the transfer case oil. If replaced, you must be sure to fully seat the seal. To do this, you will need to use a bearing press, or a bearing punch and a hammer, or a very large socket and a hammer. Be careful you do not damage the seal as you drive it home. If using a hammer technique, you can use a rag to protect the seal's surface, but don’t hit too hard.

 
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