1988 Yz490

[iowarotax]

I picked this up on ebay the other day. It didnt have any compression. I tore it down and the piston kinda came apart. Im not sure what happened to the pieces of the piston, but the lower end feels fine and the jug is mint!! There is some real fine particles in the lower end and a few pieces in the pipe. The pipe and silencer look to have been just put on! Also has a aftermarket rear shock. It also looks like it was on the standard bore.

[sandpuppi101]

I would suggest splitting the bottom ,and cleaning it out really good ,and replacing the main's atleast.The piston skirt is down there somewhere..I ain't a yamaha guy by any standard's ,but a buddy of mine had a 490 that he put in a blaster and maaaaan ,did that machine vibrate bad.Same issue ,he rebuilt the topend witout doing the bottom ,and we wished we would have done the main's at least.I know those are'nt balanced and vibrate anyway's ,but i would feel better myself finding all the lost pieces..Good luck with your project though..

[MTS]

yikes, i wouldnt run that without a fresh bore, new rod, and mains, Seals, ect,, them little particals do alot of dammage

[SCEADU]

I had an 87 and the best suggestion I can give you if you plan on keeping it to ride is to do away with all the stock motor mount bolts and buy case hardened ones and use alot of thread lock. I got mine in 89 for $200 because the fella's little brother rode it and never did any maintenance while the dude was at boot camp. At the end of summer when he got back the only motor mount left was the main one on the bottom and the frame was broken on the main beam. The pipe was in about 10 pieces. All of this was caused by vibration. I put about a grand into it back then rode it once and sold it for 2k.

[iowarotax]

Im gonna bore it and replace the crank bearings. The piston is stock bore, but the cylinder was much bigger. The shift shaft is bent, so I have to split cases anyway. The motor mounts and hardware that are on it are fairly new.

[MTS]

IF you go that far, Split the crank and at the very least do the Big end bearing, it dosnt take much to snap a rod on a bad bearing, Imo

[hancadam]

I loved mine. I had two, one a 4 speed the other a 5 speed. Sold one of them to JD here on the boards. They are bastards to start, but are fast. Way to much power in my opinion. They feel like they are going to blow up at any moment, but both of mine where very reliable.

http://img253.imageshack.us/img253/2980/blue11vy6.jpg (http://imageshack.us)

[iowarotax]

Pretty sweet bike!! Im gonna put this one back to the white and red. Im gonna get it looking good but not perfect. Im probably gonna stud it up for the ice and kick some thumper butt out on the lake.