wormsworld76 Posted September 6, 2011 Share Posted September 6, 2011 Hey Guys, I have been rebuilding an RT1 360 for a while now and I am at the point of replacing the piston and rings. The cylinder wall looks good so I just want to put the same size piston and rings in but I am having trouble identifying the size of the piston. On the top of the piston, next to the arrow it has a #75 stamped in it. Opposite of that is #8025. Can anyone tell me if this is a standard (stock) piston or is it an oversized piston. Thanks!!! Link to comment Share on other sites More sharing options...
DTGordo Posted September 6, 2011 Share Posted September 6, 2011 #75 could mean .75m oversize? You can measure it with some calipers or take it to a machinist to check it. Gordo Link to comment Share on other sites More sharing options...
Moderator Airhead Posted September 6, 2011 Moderator Share Posted September 6, 2011 yes its + 0.75mm Link to comment Share on other sites More sharing options...
wormsworld76 Posted September 6, 2011 Author Share Posted September 6, 2011 after measuring with a micrometer.....the inside diameter of the cylinder is 80.35mm and the piston is 80.15mm to 80.25 mm. So I am thinking that this piston is a .25os. Now I know that there needs to be about a .35 or less difference between cylinder wall and piston. Would it be safe to say that this is a .25os piston....i dont want to say the other guys are wrong but I dont want to purchase the wrong size piston ya know!!! Thanks Link to comment Share on other sites More sharing options...
Tommy10bikes Posted September 6, 2011 Share Posted September 6, 2011 I think you will find the guys are correct in saying it should be .75 oversize However are you sure the numbers are #75 and not # 25 Cheers TTB Link to comment Share on other sites More sharing options...
wormsworld76 Posted September 6, 2011 Author Share Posted September 6, 2011 I checked it again and it is a 75 and 8025 that is stamped on the top. I tried to post a pic on here but it didnt work! Link to comment Share on other sites More sharing options...
Teflon-Mike Posted September 10, 2011 Share Posted September 10, 2011 What's 75 thou of an inch in mm? just under 2mm.... could it mean seven and a half thou? Link to comment Share on other sites More sharing options...
Moderator drewpy Posted September 11, 2011 Moderator Share Posted September 11, 2011 its 3/4's of a mm Link to comment Share on other sites More sharing options...
wormsworld76 Posted September 30, 2011 Author Share Posted September 30, 2011 Got the piston and rings in and the bike is running...thanks for everyone's help!!! Link to comment Share on other sites More sharing options...
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