Yet Another 76 YZ400 Project Build

I picked this thing up at the end of last summer from a friend of mine who didn't want it. He is into TT 500's. His loss, my gain. For some unkown reason I have gotten my self into Yamaha's. The plan is to go through the bike and clean it up. I think. After my last episode with a resto that I got carried away with, this one will be more of a functional build.

When my buddy brought it over we had to seal the deal with one of these. The bike came from the San Fran bay area, so why not.



After a couple of those I started to really look at the bike. The gas tank is almost flawless. It has one small ding you can barely see and one you have to run your hand over to feel it.

I am sorry to be the bearer of bad news, but that gas tank SUCKS! I have a friend who can melt it for scrap and make a few bucks, please send it to me then I will send you the $$.

I like Anchor Steam, too. Please send me a six-pack along with that trashed out tank to sweeten the deal.

One of the first things I did was to take the tank off and check it out completely. It has some wear but not to bad. It's from the seat. So into the rafters it goes for safe keeping.



Took the frame all apart and got out the ol handy dandy portable sand blaster and commenced to blastin.

Think again batman. No tank for you.

Before I took the bike apart I rode it around the back yard and notice the clutch didn't engage all the way. I figured it was just an adjustment. Of course it was. While I was dinkin around after I had sprayed the frame I thought what the hell lets pull some of the motor apart. I found this :eek1



This clutch adjustment device is gone and the case is trash. Maybe not the best deal I have ever made. One of the guys on Yamahaenduro.com found a set of cases on ebay and I am on them in an instant. $65 and we are havin some things.

I had been hearing of all sorts of media blasting and kept hearing about soda blasting. After looking around on the interweb I found a home made one. These guys just stuffed a hose into the box of baking soda. I took a nalgene bottle and put a port in the bottom of it to feed the gun. Real easy stuff.



So I figured I would try it out on the wheels. I used 100psi and I am amazed how good it took off the paint and wasn't so intrusive like sand blasting. This is the shit.

The blasting is somewhat messy or should I say real messy.



Front wheel done. It came out cool. I may leave it this way instead of pulling the wheel apart and painting the hub black. It will give it the "Works" look.



A major word of caution. IF YOU DO THIS MAKE SURE YOU HAVE A DUST MASK AND GOGGLES, IF NOT YOU WILL NOT LIKE YOURSELF SOON AFTER. That is my safety tip of the day. My set up.

Another thing I wanted to address was the rear shock. When I got the bike it had zero damping. From what I remembered from back in those days is that the shock was.............well..........nothing great.

A little bit of history here. Way back in the old days I worked for Curnutt Shocks from 1975-1982. I was the only one who actually worked on the assemlby and rebuilds of the shocks except for Chuck and Charlie. So I decided I will make my own shock using the bypass technology.

I started out with making a secondary body on my lathe.



Then made up some internals with a speed sensitive (pop off) return valve.



The finished shock body.



The shock with spring on it. It calculates out right for the bike. The leverage ration is very weak at close to 1.2-3 to 1. It will have right at 8 inches of rear wheel travel.

I had to make a special bushing/spacer for the rear mount.



At the same time I had allready assembled the swing arm and had the rear wheel mocked up. I did the steering and triple clamps at the same time. For some reason the pics make it look dirty. It may be the flash.



Rear shock bolted up after some paint and trial fitting.

I disassembled the forks and took a wire wheel to the lower fork tubes to get the clear coat off them.



I sanded out some of the imperfections and took a very fine sanding pad and gave it a brushed looking finish. I like it.

So of course during this point of the build, I acquired some carpet and had to unload the whole garage and lay down some carpet. Looks pretty good after I got done. I didn't seam it as..........hey its a garage.

I then put in the fork seals using my uber expensive Yamaha seal driver tool.



Got the forks back together and started to install them.



Both installed in mock up, ready for some oil and air pressure.

I was waiting for a special box from DC Plastics with some stuff in it. It arrived and I got a little excited and moved away from the forks to work on the seat.

Before



After



More cool stuff waiting for me to mess with. I am getting excited.

I hope I am not boring anyone. I do know it is rather mundane shit at times.........but back to the forks.

Filled them up with 30wt as that is what the manual calls for to the proper amount.



I read somewhere to pump the forks about 15 to 20 times to get the air out of them. This is when I discovered that one fork leg had more oil in it than the other. Seems odd to me. I drained the forks and took measurements in the beaker again. Hmmmmmmmmm. The correct amount. Measuring from the top of the tube down to the oil level was about a 1/2" difference. I guess the maching from the factory wasn't as good as they said. Me pumpin aluminum. It was easier to do both at the same time.

On to the canisters. These are air forks with no springs. There is a high side and a low side to the pressure. They need to be somewhat accurate. I pulled out my Fox pump to adjust them accordingly. When you first put air into them you will hear a small pop which mean they are working.



You hook the pump up like this. It won't let air back feed and loose pressure. A nifty little pump.



All done. These are the original canister caps that came on the bike. They are in perfect shape. Thank God as the repops are about $100.



More to come.

I like that Fox pump! I have a bicycle tire pump but I don't think it will work as well as your Fox pump.
I bought a factory service manual - it says to use 10 wt. fork oil. 30 wt? I guess you can vary the fork oil viscosity to affect the damping, but 30 wt seems heavy. Service manual states that fork oil level is variable, too.
My bike did not have those canister caps, they are neat. Make lots more pics of your bike build.

I am getting ready to do my fork seals so I need a tool like that. I suppose it is only available from the top secret Yamaha factory works team. Scooter, any tips for installing new fork seals? I have never done this type of fork before.

I checked my service manual that came with the bike. It calls for 10-30wt oil. I set the fork oil height to the recommended specs as a starting point. Back in them olden days alot of the bikes used 30wt. CZ comes to mind. I can allways take out oil easier than disassembling the whole front end to add oil. I saw the rubber canister caps on ebay from I forget who. They were $100 per pair. Luckily mine are perfect.