Rear Axle Removal - Haynes Manual is Wrong

I should have posted this earlier (before the diff rebuild section), but just so you know, the Haynes manual is wrong about which way to remove the rear axle. (I found out the hard way). You should be tapping on the brake side (RH side) and the axle will come out toward the LH side of the bike. I wonder how many people have bashed the crap out of their axles (and ruined the threads in the process), trying to take the axle out the wrong way.

New Top End Gaskets

For some reason, these pictures keep uploading in the wrong order. Here it is going back together.

Cam chain

Cam chain tensioner

The chain guide will come out through the opening first, then the head can come off without having to remove the engine from the frame.

Put a piece of wire on the cam chain so that you can pull it back out easily.

All cleaned up.

The exhaust studs broke off when removing the nuts. We tried welding nuts onto the studs and then heating it up with a torch, but they still wouldn't come out. They had to be chopped off, drilled out & re-tapped. Thanks for the help Eric!

Rear Diff Shims - Adjusting Backlash

There is some play in the ring gear (in/out), so I'm going to make some more shims to tighten it up. It looks like .5mm on each side will remove the play and bring the backlash into tolerance as well.

Rear Diff & Axle - New Bearings and Seals

All bearings and seals were pressed in with an arbor press and various pieces of round bar. A couple pieces of round bar bad to be machined to the correct OD to fit properly.

Rear Diff - Removing Bearings and Seals

This collar and bearing required a LOT of force to remove. (Hydraulic press).

Welded a washer onto the race and used a press.

Most bearings & seals came out with an arbor press and various sizes of round bar.

Welded a piece of flat bar into the outer race and pressed out from other side.

Used a puller to remove the needle bearing outer race. There is also a small hole in the back side of the casting and you might be able to use a punch to get this one out instead of a puller.

Rear Diff Shims

Ring gear stopper shims. FYI: the stopper bolt has LH threads.

Thrust washer

Shims

Pinion gear shim

Bearing Retainer - Special Tool

This retainer nut has LH threads. Righty loosy, lefty tighty.

Rear Diff Rebuild

No wonder the rear wheels didn't want to turn!

Rear Diff Rebuild (Final Drive)

Identification - Haynes Manual is Wrong

The Haynes manual was wrong about the model/type. Ignore that section of the book and double check your specs below:

Big Bear 350 Model List
YFM350FW
Year	Model	Type
1989	YFM350FWW	3HN2
1990	YFM350FWA	3HN4
1991	YFM350FWB	3HN9
1992	YFM350FWD	3HNB
1993	YFM350FWE	3HNE
1994	YFM350FWF	3HNH
1995	YFM350FWG	3HNL
1996	YFM350FWH	3HNS
YFM350FWB
Year	Model	Type
1997	YFM35FJ	4WU2
1998	YFM350FWBK	4WU7
1999	YFM350FWBL	5FT3
YFM350FWU
Year	Model	Type
1988	N/A	2HR0
YFM350U
Year	Model	Type
1996	YFM350UH	4UH2
1997	YFM350UJ	4UH5
1998	YFM350UK	4UH8
YFM350UBL
Year	Model	Type
1999	N/A	5FE3
YFM350FWSP
Special
Year	Model	Type
1997	YFM350FSJ	3HNV
YFM350FW
Special Edition
Year	Model	Type
1995	YFM350FSPG	3HNP
YFM350FWSP
Special Edition
Year	Model	Type
1996	YFM350FSPH	3HNU
1998	YFM350FWSPK	4UM3
1999	YFM350FWSPL	4UM6
2000	YFM35FSM	4UM8

Broken Idler Gear Shaft - Solution

Solution: I had a machinist friend make a new shaft with extra nubs on each end, 8mm OD x 12mm. There were pilot holes in the bottom of each broken boss measuring 7.5mm OD. (See previous pictures). I used a collar with a 12mm OD (size of the shaft) and 8mm ID, clamped the collar into the broken boss, and used an 8mm hand reamer to open up the holes and adjust the fit of the new shaft. The collar kept everything in line and the engine case slides on perfectly. Now let's see if it breaks again! I don't know the original cause of the broken castings, as the starter clutch is smooth and the gears all look good. (??)

Shown with the shafts and gears in place

Starter Idler Gears - Broken Case & Cover

The second starter idler gear shaft had broken out of the engine case and cover.

Yamaha Big Bear Rebuild

Due to a lack of information on the web about certain aspects of fixing up a Yamaha Big Bear, I have decided to post some info on this subject, with the hope that it will help someone out. I am not an expert or anything, but I do enjoy tinkering in the garage. My latest project is a 1997 Yamaha Big Bear 350 4x4 that I will be fixing up over the winter. I hope some of these posts will be helpful to someone who is taking on a similar project.