new guy piston question

roadstar06

roadstar06

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so i am attempting to find out ring end gap and i totally messed up my pistons because i couln't get top ring off of either piston, that being said I need new pistons :),,,the top says 967. I know what that means but in trying to find a set is proving to be a hassle..can I use the 954 or will it be too small? do they really make 6 different os pistons before you hit big bore?or is it only the ring that changes?? I saw a nos set on ebay but top says .75? is that 3 o/s or 74.750?? I wrote to the guy but no response yet, also how many of you did the big bore upgrade? is it worth the time and money?? I got the time but low on dough..:banghead:
 
The target measurement for XS650 pistons and cylinders is the clearance of 0.002".
The cylinders must be honed for proper ring seating. This opens up the cylinder slightly.
After honing, you can measure the bores to see if you can stay within clearance limits with new pistons.

So, what this is saying, is that you don't need to fret over those particular 74.9xx OEM piston sizes. Those markings only applied to the factory when assembling brand-new engines with brand-new cylinders.

Replacement pistons are available in 75.0mm, 75.25mm, 75.5mm, 75.75mm, 76.0mm, (0.25mm increments). But, for any size, they're not precisely the same, and measurements must be taken to ensure the clearance values.

Sure, a lot of folks have just stuck "close enuff" pistons and rings in there, and gotten away with it. Good enuff for mild riding, or to sell the bike, or later start asking questions about smoking engines with oil fouling plugs.

Without all the measurement and servicing tools, your best path is to simply acquire a "next oversize" set of pistons and rings, deliver them with the cylinders to the machine shop, and let them bore/hone the cylinders to the proper size to fit the pistons...
 
TwoManyXS1Bs said:
The target measurement for XS650 pistons and cylinders is the clearance of 0.002".
The cylinders must be honed for proper ring seating. This opens up the cylinder slightly.
After honing, you can measure the bores to see if you can stay within clearance limits with new pistons.

So, what this is saying, is that you don't need to fret over those particular 74.9xx OEM piston sizes. Those markings only applied to the factory when assembling brand-new engines with brand-new cylinders.

Replacement pistons are available in 75.0mm, 75.25mm, 75.5mm, 75.75mm, 76.0mm, (0.25mm increments). But, for any size, they're not precisely the same, and measurements must be taken to ensure the clearance values.

Sure, a lot of folks have just stuck "close enuff" pistons and rings in there, and gotten away with it. Good enuff for mild riding, or to sell the bike, or later start asking questions about smoking engines with oil fouling plugs.

Without all the measurement and servicing tools, your best path is to simply acquire a "next oversize" set of pistons and rings, deliver them with the cylinders to the machine shop, and let them bore/hone the cylinders to the proper size to fit the pistons...
Click to expand...
thanks 2many, I was thinking the same thing.25 would be the first cut on these jugs. i'm going to see machinist tomorrow and have him measure cylinder as i cant get an accurate number, i measured top and bottom of cylinders and those numbers are good 75- a hair. i wonder why Wiseco doesn't make pistons to fit it? only have 80-81mm. oh well...
 

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