gyraffoclops
XS650 Member
I just took apart my engine and the number 3 and 1.00 are stamped on top of the pistons. What does this mean and what size piston rings should I buy? I'm a bit of a rookie on engine rebuilds. Thanks
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Piston size?
- Thread starter gyraffoclops
- Start date
rebel542
Old Timer
The 3 doesn't really mean anything but the 1.00 means it's 4th oversize. It's been bored to the largest oversize piston Yamaha makes. A standard will have 96 stamped in the top. Always measure to double check. Hope this helps.
On a stock piston, the numbers stamped into the top of the piston is the piston size. When they make pistons they don't all come out the exact same size. They measure them and match them by size. The sizes are all 74.xxx mm. The xxx part of the number is stamped in the piston. If you only find two didit then clean some more it's there.
With a matched set of pistons they bore the cylinders to match the pistons. All bors are 75.xxx The xxx is printed on the cylinder sleeves below the jugs.
Say the piston says 955 that's 74.958. The sleeves sat 010. That's 75.010. I have set wqith those numbers. Now subtract the piston from the sleeve and you come up with the piston to cylinder clearance when it was assembled. In this case, 75.010-74.958= .052, that's right in the middle of the .050-.055 spec.On oversize pistons the are marked with the oversize in mm the first over size is 25 as in 75.25 mm, second is 50, as in 75.50. Your 1.00 is 76 mm or fourth over. The 3 might be some other companies third over.
I would measure them. Pistons and bores.
The stock sleeves can be bored out to 12th over. That's a 78 mm bore. This makes the 650 cc engine a 707 cc engine.
If you don't have tools to measure, most any machine shop does and will measure your parts for a small fee.
Once you find out what you have, then you can decide what to do.
Hoo's Racing has those 707 cc pistons.
Leo
With a matched set of pistons they bore the cylinders to match the pistons. All bors are 75.xxx The xxx is printed on the cylinder sleeves below the jugs.
Say the piston says 955 that's 74.958. The sleeves sat 010. That's 75.010. I have set wqith those numbers. Now subtract the piston from the sleeve and you come up with the piston to cylinder clearance when it was assembled. In this case, 75.010-74.958= .052, that's right in the middle of the .050-.055 spec.On oversize pistons the are marked with the oversize in mm the first over size is 25 as in 75.25 mm, second is 50, as in 75.50. Your 1.00 is 76 mm or fourth over. The 3 might be some other companies third over.
I would measure them. Pistons and bores.
The stock sleeves can be bored out to 12th over. That's a 78 mm bore. This makes the 650 cc engine a 707 cc engine.
If you don't have tools to measure, most any machine shop does and will measure your parts for a small fee.
Once you find out what you have, then you can decide what to do.
Hoo's Racing has those 707 cc pistons.
Leo
It ain't rocket science , measure the bore ...
~Dennis
~Dennis
gyraffoclops
XS650 Member
Thanks guys, I've got another dumb question. If i get my cylinders rehoned do I still buy 1.00 piston rings to put on the pistons? or do i need a bigger size. I've never got cylinders honed before and am not sure how much material it actually removes.
It shouldn't remove much at all, if any, if done properly and with the right type of hone. You want to use the bottle brush style or Flex hone, not the 3 or 4 stone hone. The stone hones can remove material and enlarge the bore. In fact, when a cylinder is bored, it's bored close to size, then stone honed to size, then flex honed to give it the final finish best for seating rings.
rebel542
Old Timer
You will want to purchase 1.00 rings, 4th oversize.
