Cylinder Bore..... I am confused....

[stever250r]

I go to install the cylinder and piston on the 88 tonight, and realize that the piston that was sent with the cylinder is stamped .030 on top.... 66.75mm bore...

WAY TOO BIG......Anyhow.. I measure my cylinder bore, and I keep getting 66.40mm..... Could this be right? Why not 66.50mm??

I cant find a piston for a 66.40mm.. All I see are 66.25mm or 66.50mm....

I have measured over several times and cant convince myself that this a 66.50 mm bore and I now have no idea what piston I need to order..

I am afraid if I order a 66.50mm the clearance will be too tight....

Can anyone help me out..???

[dirtycj5]

wossner has a 66.44

did you have the cylinder bored? what i do when i bore the cylinder i take the cylinder and piston with the rings to the machine shop. also with most pistons there is the set up size on the box or on a paper for the boring

[dirtycj5]

maybe check the caliper that you useing to measure?

[89trx250r]

Im pretty sure weisco makes only .25 .50 .75 and then whole sizes im going through a similar problem im about to order a new piston to freshen her up for the season and im at 68.40mm at the moment and i measured everywhere my caliper had access so i personally thought the 68.50mm piston would be good to give the right amount of clearance between the rings and the sleeve hopefully one of the motor guys can chime in here for us both....

[fearlessfred]

Originally posted by stever250r
I go to install the cylinder and piston on the 88 tonight, and realize that the piston that was sent with the cylinder is stamped .030 on top.... 66.75mm bore...

WAY TOO BIG......Anyhow.. I measure my cylinder bore, and I keep getting 66.40mm..... Could this be right? Why not 66.50mm??

I cant find a piston for a 66.40mm.. All I see are 66.25mm or 66.50mm....

I have measured over several times and cant convince myself that this a 66.50 mm bore and I now have no idea what piston I need to order..

I am afraid if I order a 66.50mm the clearance will be too tight....

Can anyone help me out..??? does the piston you have fit in the cylinder

[265 sleeper]

My not be a 250r piston or different brand wossner sudco

[C-LEIGH RACING]

Wiseco pistons are under sized as to what is marked on the box.

Like the #526MO6650, a 66.50mm piston, that piston will measure out at 66.44mm.
If that is the piston kit you have, then your cylinders finished bore should measure 66.50mm, which will be 0.0030 larger than the piston to allow piston to cylinder bore clearance.

?, What is the part number stamped on top of the new piston kit you have.
?, Are you using a T bar to measure down in the cylinder bore, or just a caliper at the top & bottom.

Always, when getting a cylinder bored & honed, take the new piston your going to use with you, so the boring machine operator can measure it first & bore the cylinder to the proper size.

Another tid bit of info,
When your looking in a Wiseco piston catolog, & say your looking at the #526MO6650 piston kit, which is a 66.50mm piston, if you look to the right of that listing it has a ring set part number listed as well, #2618CD, that ring set part number is realy the size the cylinder should be bored to, which would be 2.6180" & would be 0.0030 piston clearance.

It sometimes will get confusing with measurements on a box & what a new piston will measure, & + those measurements will be in mm & the USA is measuring eveything in inches, so it can get confusing real quick.
Neil

[265 sleeper]

Also look inside the piston is there any marks is it a cast piston or forged .


I believe he stated the piston was mark .30 on it

[stever250r]

Originally posted by C-LEIGH RACING
Wiseco pistons are under sized as to what is marked on the box.

Like the #526MO6650, a 66.50mm piston, that piston will measure out at 66.44mm.
If that is the piston kit you have, then your cylinders finished bore should measure 66.50mm, which will be 0.0030 larger than the piston to allow piston to cylinder bore clearance.

?, What is the part number stamped on top of the new piston kit you have.
?, Are you using a T bar to measure down in the cylinder bore, or just a caliper at the top & bottom.

Always, when getting a cylinder bored & honed, take the new piston your going to use with you, so the boring machine operator can measure it first & bore the cylinder to the proper size.

Another tid bit of info,
When your looking in a Wiseco piston catolog, & say your looking at the #526MO6650 piston kit, which is a 66.50mm piston, if you look to the right of that listing it has a ring set part number listed as well, #2618CD, that ring set part number is realy the size the cylinder should be bored to, which would be 2.6180" & would be 0.0030 piston clearance.

It sometimes will get confusing with measurements on a box & what a new piston will measure, & + those measurements will be in mm & the USA is measuring eveything in inches, so it can get confusing real quick.
Neil

Thanks Neil...... What I did, was buy a used stock cylinder and piston combo... The cylinder and piston were described as running at the time it was disassembled so although not a good practice I was going to roll the dice and just reassemble everything and get whatever life I could get out of it for the time being, and then bore and replace the piston kit when it did go out on me, whether that was a day, a week, a month...........Anyhow, the problem came when I went to install everything and then realized the used piston that was sent with the cylnder could not have been the piston that came out of it... It was stamped .030 on top and would not fit my cylinder bore even with the rings removed..

At this point, I just figure okay, I will buy a new piston and ring set to match the current cylinder bore... I do not have a set of T guages so I measured the bore with a digital caliper at the top and kept getting a reading right at 66.40mm give or take .01mm.

Thats where I got confused. I dont understand why this bore would be at 66.40mm if noone makes a piston for that size bore.....I would like to think that the cylinder bore is actually 66.50 mm and that my measurements are off.. I was just trying to make sure of this before ordering a new Wiseco #526MO6650 piston just to find out that it was not correct...

The cylinder and bore both look really clean, and I was only trying to get around boring this if I didnt really have too....

[C-LEIGH RACING]

It could be the piston that was ran in that cylinder was a 66.25mm & sometime after, the cylinder has been honed more just to make it look good & ended up being the 66.40 measurement you are getting.
Could be as well, the other owner had several cylinders & got the used piston mixed up

I dont know how to convert mm over to inch measurements, but 66.25 up to 66.40mm I'm guessing would be close to 0.010 to 0.015 clearance.

If you check around say maybe like at a tool sale, you can find those T bar sets real cheap like $10 or $15.00.
A traveling tool sale company named Homier Tools I know has them & they have a web site but dont know how it is listed.

Your probably going to need a new piston kit & then get the cylinder bored to the proper size, only problem, that cylinder needs to be measured so to get the right size piston kit.
You could in a pinch, have that used 66.50 piston measured & then have the cylinder hone finished out to the size of that used piston.
Neil

[stever250r]

There is no doubt that the previous owner had a few pistons around and mistakenly sent me the wrong one. I have spoken with him and he says that the piston that matched my cylinder had fallen behind his work bench and he had sent the wrong one. He is mailing me out the piston that he says matches this. Cylinder so I guess I will see what I have after it gets here. Could you send me your shipping address to my email at sroarksr@gmail.com?.....I might end up just sending this out to you. I also want.to send you a ESR 310 PC cylinder to port for my Laeger Engine.

[mx91a]

It could be set up for a CR250 piston. Their stock bore is 66.40mm

[destey]

Just to eliminate this as an issue, try measuring the bore with a bore gauge or a telescoping gage then measure that with a micrometer. Shouldn't be measuring a bore with a caliper.