Ty 175 Shielded Gearbox Bearing

[mmmexico]

I am getting ready to put my TY 175 back together. I am concerned about the gearbox bearing on the right hand crankcase half. When I took the bike apart I could see that this bearing was shielded on the side facing out and open to the inside of the gearbox. That made sense to me because this arrangement allows the bearing to receive lubrication from the oil flying around the inside of the gearbox. I ordered new bearings all around and the bearing that I received for this application was shielded on both sides...so how does it get any lubrication?

Just wondering...The part was a Yamaha part with the correct Yamaha part number...So I would appreciate any advice or thoughts.

By the way, my build is being documented on my blog http://meditarivemachinery.blogspot.com/ in case any of you would be interested in following along.

Hope that you can help me with the bearing...and I hope to see you on the Blog...

Mike

[lineaway]

Pop the shields off. two stroke oil lubes the bearings of both mains.

Edited May 27, 2014 by lineaway

[feetupfun]

As you found with the motor when you pulled it apart, they usually have only one metal shield on that bearing and it is located on the outside of the bearing.

That bearing has a shield to better manage where the oil goes inside the gearbox and primary drive case while you are riding and falling off.

The reason the shield goes on the outside is that there is a better oil supply to the bearing via the gearbox side, compared with the primary drive side.

It is common for bearings to be supplied with two shields, or two seals, to reduce inventory in the supply chain. Yamaha have been rationalising many parts in their supply chain for many years, so nowadays you might buy a genuine Yamaha magneto case breather for example, or a genuine nut or bolt for a TY175, and find it is a different colour or finish than the original item, but it still fits and works as intended.

The unwanted shield can be easily removed

Edited May 27, 2014 by feetupfun

[feetupfun]

Michael I looked at your blog, but was not able to comment on there about the rebore on the TY175. Pistons are made smaller at the top (at room temperature) because the top of the piston expands more in diameter than the bottom of the piston when the motor is running. It is usual to use the diameter of the piston at skirt height for setting the clearance and yes it is very unusual for a cylinder rebore specialist to suggest that the customer should achieve the desired clearance by shaping the piston. The machinist should either bore to the right size, or bore undersize and then hone to size

[mmmexico]

Thanks feetupfun for the information. I'm glad I asked. Yes, I agree, it seemed unusual to me to have the machinist suggest that I work over my piston with sandpaper to achieve the desired clearance. Here in the backwoods of Mexico you have to accept some compromises. I am going to go over the piston skirt again to insure that the clearance is correct...and then after running for an hour or so I will take it apart and take a good look at the piston.

My assumption, which appears to be wrong, was that a forth oversize piston (67mm) would uniformly be 67mm from top to bottom and I further assumed that boring the cylinder to 67.045 would achieve the correct clearance. Based on my measurements, if the cylinder was taken out to 67.045mm it would have resulted in a clearance at the top of the piston of .095mm...essentially worn out according to the Yamaha manual which says that the greatest acceptable clearance is .1mm...no where is there any suggestion that these measurement are taken at the skirt. Thanks again...

Mike

P.S. I will be taking off the inside shield from the bearing