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Postby Blurredman » Fri Dec 15, 2017 4:57 am

Hi guys,

I'm looking to do some re-bore on some of my cylinders.

I have a 300cc barrel and piston that are very badly worn now. It is a converted 250 barrel with an original size 300 piston being 75.46mm. The barrel is pretty much almost as worn to the extent that a 76mm piston would fit into it. It has almost 0.4mm clearance on one side (0.15 to 0.2mm if i center the piston). I'm going to get it rebored and a 76mm piston installed. With 15 thou clearance I understand. I shouldn't think there would be too much trouble doing this, considering the bore is almost as big as 76 anyway?! Right?

And on the subject I have a spare cylinder and piston which were seized together on a bike I bought that I wish to re-install, and found out the piston diametre is 70.5mm which is 3rd oversize. I can obtain 71mm pistons, and considering the above 300cc conversion I shouldn't have issues with putting a 4th oversize in. At 13 thou clearance.

1979 Suzuki TS185ER - 9,00 miles - Mud :)
1981 Honda CX500B - 77,000 miles - Long Distance :)
1987 MZ ETZ300 - 29,000 miles - Sun :)
1990 MZ ETZ251 - 39,500 miles - Commute :) - When it gets to 40k miles I will retire it for engine work
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