DT1 flat track project

I ended up buying three OEM Yamaha bearings and three Nachi bearings.


I bought the Nachi bearings from http://www.vxb.com/. They look to be just as good as the stock Koyo bearings, and are good replacements to save money or when the OEM part isn't available.


You can identify bearings by the markings to help figure out what you need.. This is one of the new Nachi main crankshaft bearings, kit 9871. The Yamaha part number for this is 93306-30630-00. Note the '6306' in the middle of the part number. The 'C3' is the clearance. A 'Z' after a number has one side shielded, and 'ZZ' has both sides shielded. 'N' has a snap ring. Some good info I got from Deet on the Yamaha Enduro forum, one of the transmission bearings is Yamaha part number 93306-20306-00, and early 6203 bearings like in my engine are 42mm OD, where a new 6203 from Nachi is 40mm, so be sure to check the actual bearing size. With that one I ordered a Yamaha bearing, since it is still available.


I put the bearings in the freezer, and heated the cases to install the bearings. I temporarily put the cases together to measure main bearing width and compare to crank width to determine if the original shim would work. I then used the crank tool to pull the crankshaft into the right side case, making sure not to forget the shim, and then put the transmission in with all of the shims.


I'm using ThreeBond 1194 for the case sealant. About the easiest and neatest way to apply it is with a small paint brush with the sealant in a plastic spoon. It is very stringy, so you can catch the strings on the spoon after dipping the brush.


I then used the crank tool to mate the cases, keeping them even as I went.


I don't know of a kit for the case bolts, so I got some stainless steel socket head fasteners from ebay seller Wise Guy Bolts. These are M6-1.00, with five 45mm, one 60mm, and seven 65mm long. With stainless going into aluminum I use anti-seize lubricant to prevent any galling.


The seal kit is from ebay seller Rusty Riders.


This is the nickel plated brass fitting that I tapped the case for, to replace the stock transmission vent. It is 3/16" ID hose x 1/8" NPT.


Since I won't be using a tachometer, I got a K&N tach plug from ebay seller vintagepartsgirl that eliminates the tach drive.


Here is the bottom end pretty much done.