I am doing top end work done on my 250 tb (bore job, oversized piston) & was wondering how much
I can have the head milled & still use reg. gas? I am putting in a .5mm oversize piston the rest of the
bike is stock with a uni air filter, I have heard polaris is conserveative on compression it only had
110psi just after it was broke in. will the wiesco piston & rings raise compression over the stock piston?

 

You can mill the head .20 but no more. It will help a little but you really should get a port job if you have it apart. This helps out greatly. Just changing the piston will not raise compression . It will only get it back to new stock compression. If you bore out the jug go as small as you can. You may not even need a bore job. The bore job does nothing for performance. It just adds life to the jug. If you still have 110psi then all you may need to do is hone the cylinder then get a stock size wiesco piston. This way you will have many more rebuilds in the long run before you have to resleeve. Dont bore anymore then you have to.

 

The motor had 90psi checking it after it was good & warmed up,it was starting hard, when I took it
apart the ring end gap was .040 when checking the rings in the cylinder, the ser. manual says it should be .009 to.018 so the rings are worn. I wanted the bore job so the cylinder was round again and it would be longer before I need to take it apart again, .5mm is the next sized up. Wiesco has pistons for 6 bore jobs before it needs to be resleeved. On the head milling did u mean .20mm or .020 thousands? thanx for help.

 

I mean .020 sorry.

 

thanx 2manytoys, parts came today, off to the shop for the bore job tomorrow!