actual cylinder diameter to bore to...

[mk2dubbin]

i am having a friend bore the cylinder for me and i already have the wiseco 66.75mm piston to go in the new bore. what i need to know is what i need to bore the cylinder to...

stock piston diameter is 66mm, and piston to cylinder clearance is .035-.040mm yielding a stock final bore size of 66.035-66.040 - correct?

i don't have the wiseco piston in front of me to verify but i read that they are undersized so that the final bore would be (in my case) 66.75mm. is that correct? i want to be sure that i don't need to end up with a 66.785-66.790mm bore before this gets machined...

Thanks!

 

[joeak47]

i am having a friend bore the cylinder for me and i already have the wiseco 66.75mm piston to go in the new bore. what i need to know is what i need to bore the cylinder to...

stock piston diameter is 66mm, and piston to cylinder clearance is .035-.040mm yielding a stock final bore size of 66.035-66.040 - correct?

i don't have the wiseco piston in front of me to verify but i read that they are undersized so that the final bore would be (in my case) 66.75mm. is that correct? i want to be sure that i don't need to end up with a 66.785-66.790mm bore before this gets machined...

Thanks!

The wiseco box gives you the dimensions to bore too,but check everything.
On the side of the box you will se something like...
2638CD (this is for a 67 mm piston "CD" is cylinder diameter to bore too. This should give you .002 cylinder wall to piston clearance.
I say trust nothing and check everything. even though the box says it,check everything anyway. Check the piston diameter at the skirt,bore diameter all over the place (top,middle and bottom,and 90 degrees to those points once again),and come up with an average. Also check for bore taper.

Kind of like the old saying...measure twice and cut once.

 

[sicivicdude]

i am having a friend bore the cylinder for me and i already have the wiseco 66.75mm piston to go in the new bore. what i need to know is what i need to bore the cylinder to...

stock piston diameter is 66mm, and piston to cylinder clearance is .035-.040mm yielding a stock final bore size of 66.035-66.040 - correct?

i don't have the wiseco piston in front of me to verify but i read that they are undersized so that the final bore would be (in my case) 66.75mm. is that correct? i want to be sure that i don't need to end up with a 66.785-66.790mm bore before this gets machined...

Thanks!

There are two different ways manufacturers handle bore sizes. Some state the ACTUAL piston diameter and the piston to cylinder clearance is above that. Most state the ACTUAL bore size and the piston is smaller!

Yamaha is the latter and wiseco makes their pistons to match. A 66.75mm piston is ACTUALLY only 66.70mm. The cylinder should be 66.75mm and the stated piston to cylinder clearance of .002" (or .05mm) is made by having the piston slightly smaller than the hole.

If you are having it bored, you are MUCH better off to give the piston to the machinist so he can accurately measure the piston size and make the hole fit it. Wiseco is VERY accurate and that 67.75mm piston will be 66.70mm but it's better to check anyway, you never know what the ride from wiseco to you was like!

 

[OConnor Racing]

We log the outside diameter of every piston that comes to the shop on a bell curve. We’ve seen this part number many times. The smallest OD we’ve ever recorded was 2.6659” and the largest was 2.6663” for a difference of .0004”. For this reason, you want the machinist to have the piston in hand before he begins any work. Another thing to consider is the difference in calibration from one micrometer to another. Blocks certified to NIST (National Institute of Standards and Technology) need to be used for calibration of the devices used by both parties. I’m sure Wiseco has them. Who knows how calibration is taking place on the other end. If all measurements are being done by the machinist doing the job, you’ll be fine. Wiseco labels their boxes with a recommended minimum cylinder wall to piston clearance. In this case, the dimension is .002”. The other numbers on the front of the box are the part numbers contained in the piston kit. S486 is the piston pin, CW16 is the number for the retaining clips and 2628CD is the part number for the rings. The ring part number does reference the cylinder diameter but the CD suffix stands for the type of rind being used, not cylinder diameter. Wiseco uses 18 different types of rings in two stroke motorcycle applications and 31 in four strokes. The suffix (CD) is also the retail price code of the rings.

 

[Awk08]

Another thing to consider is the difference in calibration from one micrometer to another. Blocks certified to NIST (National Institute of Standards and Technology) need to be used for calibration of the devices used by both parties. I’m sure Wiseco has them. Who knows how calibration is taking place on the other end.

calibrate huh ?
Isn't that a province in Italy

 

[mk2dubbin]

Thanks for the clarification guys! We will measure the piston and bore accordingly to maintain required clearance.

 

[slickerthanyou]

We log the outside diameter of every piston that comes to the shop on a bell curve. We’ve seen this part number many times. The smallest OD we’ve ever recorded was 2.6659” and the largest was 2.6663” for a difference of .0004”. For this reason, you want the machinist to have the piston in hand before he begins any work. Another thing to consider is the difference in calibration from one micrometer to another. Blocks certified to NIST (National Institute of Standards and Technology) need to be used for calibration of the devices used by both parties. I’m sure Wiseco has them. Who knows how calibration is taking place on the other end. If all measurements are being done by the machinist doing the job, you’ll be fine. Wiseco labels their boxes with a recommended minimum cylinder wall to piston clearance. In this case, the dimension is .002”. The other numbers on the front of the box are the part numbers contained in the piston kit. S486 is the piston pin, CW16 is the number for the retaining clips and 2628CD is the part number for the rings. The ring part number does reference the cylinder diameter but the CD suffix stands for the type of rind being used, not cylinder diameter. Wiseco uses 18 different types of rings in two stroke motorcycle applications and 31 in four strokes. The suffix (CD) is also the retail price code of the rings.

WOW! Nice Info! KOR never lets ya down!