Re: XR4 Repair/build/DS thread
Another update. I got up early this morning and did some things. I was really curious to see what the top ends looked like, and really just to familiarize myself with this motor. Let's just say I REALLY like how this motor is built. It just looks hearty. That being said, this thing does have some issues. I'm positive I'm the first person to see inside of this motor since it was manufactured. There is a ridge of carbon at the top of the cylinder. I can't tell if its worn into the bore, until I get the carbon cleaned off. The cylinder head had a lot of carbon buildup, but I got a lot of it off with some acetone, brass bristled brush, and minimal effort. (Phone died prior to pics) I'll probably just take it to my machine shop and have him bead blast it, and re-lap the valves, and install new stem seals. He also blasts through the exhaust ports to clear the carbon out of the exhaust plenum. He charges a VERY reasonable price, and he's the guy I used for the KLX that I just got done with.
I haven't checked piston availability for these, but I know I want to use cast pistons due to their lighter weight, and thermal stability. (Pro-x or Namura) I like the idea of running a tighter piston bore clearance. The current bore is spot-on 85mm, at to top of the bore. I'll probably go .020" over, if available. Forged pistons have their place, but a low compression xr400 isn't really it, IMHO.
Next up, is painting the frame. I used a sctoch brite pad to get all the dirt and grime off, but only after power washing it thoroughly. After a dry sctoch brite pad, I used a wet one, doused in acetone. I made sure not to get through the factory powder coat. It IS in fact the best primer if prepped correctly. After that, I applied two light coats of Bull Dog adhesion promoter. Guys, this stuff is awesome. If you prep motorcycle plastics, and get the surface evenly roughed up, you can apply this stuff, then regular 2-part (chemically hardened/ catalyst) base coat paint with a flex additive in it, and it lasts for a long time. I recommend this product to anyone.
I used Duplicolor Perfect Match aerosol enamel, in Toyota Graphite metallic. This paint is also a very good product. Flows out well, and applies really evenly, with great coverage. Also its available at every major auto parts chain store. After this I'll finish it with a product called SprayMax 2k clear. Its a catalyst clear that's impervious to gas and any other kind of chemical a xr400 can spew on it. Basically the same stuff as automotive clear. It has an internal chamber with the catalyst Gardner that you "activate" prior to use. After it is activated, the clock is ticking. In 45 minutes, it'll be hardened inside the aerosol can. The catch is, you gotta let the enamel base coat dry for a few days. Enamel paint shrinks as it dries, and really takes about 3-5 days (depending on weather) for this process to be complete. Prior to clear, I'll go over it with wet 1200 sand paper. Pics are respective to the text above
All of this torn up metal was in the pick up screen. There was actually a little but more too.
My messy table. I've never worked from one of these before, but I love it. Normally o work off my 36" high work bench. It gets crowded quickly
Very carefully masked off the Vin, and manufacturers tag. It thinks these are the little touches that make the nice bikes really stand out. (I obliterated the Vin stamp. I don't like the idea of the VIN being out for the world to see)
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