2002 CR125 Piston replacement question

bents
Posts
3282
Joined
12/31/2009
Location
CA
Fantasy
710th
Edited Date/Time 5/18/2016 2:40pm
Ok boys,

Put down your tinfoil hats and riddle me this: I took my top end off and went on to the Bud Racing Website to look for a replacement while I also needed to order a gasket for a bud racing head, and there are five different bore sizes that come up, from 53.93 to 53.97. What gives? It is a stock bore. How do I know which one to buy?

Thanks for any and all advice.
|
RPM68
Posts
1560
Joined
11/18/2006
Location
DFW, TX US
5/18/2016 1:17pm
get the big one and make sure the cylinder matches. you're only talking .003 different in variation.
5/18/2016 1:21pm
... .003 mm = 0.00011811inch.... .0001 is 10 thousandths...
...which is nothing...
peelout
Posts
17872
Joined
1/6/2011
Location
Ogden, UT US
5/18/2016 1:25pm Edited Date/Time 5/18/2016 1:41pm
best advice i can give is one of these.

if you leave the gas cap off it only takes one


RPM68
Posts
1560
Joined
11/18/2006
Location
DFW, TX US
5/18/2016 1:43pm
peelout wrote:
best advice i can give is one of these. if you leave the gas cap off it only takes one [img]https://i.imgur.com/3msmK0s.gif[/img]
best advice i can give is one of these.

if you leave the gas cap off it only takes one


wait until you see mine when it's done. My 02 cr125 is gonna be pulling holeshots in the 65 class...

seriously, its going to be legit.

The Shop

bents
Posts
3282
Joined
12/31/2009
Location
CA
Fantasy
710th
5/18/2016 1:46pm
Peely,

Yes I have read your disdain for these bikes over and over again, and I get it! I bought this bike off Joel Ard, and it is a trick little scoot and the motor has been done to the 9's and it has every bell and whistle on it. While I'm sure a YZ of a similar vintage would probably have it covered, it is a ton of fun to ride and goes wherever you point it. A 125 is for the pure hell of it, and I love it.

I just want to make sure I buy the right piston for it and I understand the tolerances are close, I just don't to miss anything and there are guys on here who have a wealth of experience building these things. As I just learned through Service Honda, there are two different cylinders on these bikes within certain VIN #'s and they are marked A and B, so I have to make sure I buy the right piston for the right cylinder.

I am still open to any aftermarket opinions or do I stick with OEM?

peelout
Posts
17872
Joined
1/6/2011
Location
Ogden, UT US
5/18/2016 1:49pm
bents wrote:
Peely, Yes I have read your disdain for these bikes over and over again, and I get it! I bought this bike off Joel Ard, and...
Peely,

Yes I have read your disdain for these bikes over and over again, and I get it! I bought this bike off Joel Ard, and it is a trick little scoot and the motor has been done to the 9's and it has every bell and whistle on it. While I'm sure a YZ of a similar vintage would probably have it covered, it is a ton of fun to ride and goes wherever you point it. A 125 is for the pure hell of it, and I love it.

I just want to make sure I buy the right piston for it and I understand the tolerances are close, I just don't to miss anything and there are guys on here who have a wealth of experience building these things. As I just learned through Service Honda, there are two different cylinders on these bikes within certain VIN #'s and they are marked A and B, so I have to make sure I buy the right piston for the right cylinder.

I am still open to any aftermarket opinions or do I stick with OEM?

for what it's worth it was just a joke.

also, i only buy OEM pistons/rings, always have and always will
5/18/2016 1:49pm Edited Date/Time 5/18/2016 1:50pm
bents wrote:
Peely, Yes I have read your disdain for these bikes over and over again, and I get it! I bought this bike off Joel Ard, and...
Peely,

Yes I have read your disdain for these bikes over and over again, and I get it! I bought this bike off Joel Ard, and it is a trick little scoot and the motor has been done to the 9's and it has every bell and whistle on it. While I'm sure a YZ of a similar vintage would probably have it covered, it is a ton of fun to ride and goes wherever you point it. A 125 is for the pure hell of it, and I love it.

I just want to make sure I buy the right piston for it and I understand the tolerances are close, I just don't to miss anything and there are guys on here who have a wealth of experience building these things. As I just learned through Service Honda, there are two different cylinders on these bikes within certain VIN #'s and they are marked A and B, so I have to make sure I buy the right piston for the right cylinder.

I am still open to any aftermarket opinions or do I stick with OEM?

..OMG....all over .0001, a 10 thousandth...if its so important why don't all other piston manufactures do it....
cslacker
Posts
325
Joined
6/6/2014
Location
Glendale, AZ US
5/18/2016 2:13pm
I guess I'm a bit confused by peoples math here? He says above "from 53.93 to 53.97".

Now I haven't been in a math class in quite a while but that appears to me to be .04, not .003....
And .04mm= 0.0015748 inches, not .0001

And I'm honestly not saying that even that would matter, but at minimum lets try to use the correct numbers.

The real answer is if you want to do it right measure your bore, then find out the tolerances the piston calls for, and make your choice based off of that. Or, just call the company and ask, but they might tell you to measure also. The whole point of offering different pistons is to get an ideal fit but it's your call.

Or just go with 53.94 which is the stock size...
Tracktor
Posts
2344
Joined
8/17/2006
Location
The RTF/Amboy, WA US
5/18/2016 2:14pm
We have an '02 Cr125 with the HPP cylinder. I have ran pretty much every brand of piston and never had a failure so I say whatever is easy & cheap to get. Vertex & Wiseco are my usual go toos since they make specific pistons for my applications but used Pro-X with good results also...........and with some work it's not hard to make these into YZ eaters........
5/18/2016 2:33pm
cslacker wrote:
I guess I'm a bit confused by peoples math here? He says above "from 53.93 to 53.97". Now I haven't been in a math class in...
I guess I'm a bit confused by peoples math here? He says above "from 53.93 to 53.97".

Now I haven't been in a math class in quite a while but that appears to me to be .04, not .003....
And .04mm= 0.0015748 inches, not .0001

And I'm honestly not saying that even that would matter, but at minimum lets try to use the correct numbers.

The real answer is if you want to do it right measure your bore, then find out the tolerances the piston calls for, and make your choice based off of that. Or, just call the company and ask, but they might tell you to measure also. The whole point of offering different pistons is to get an ideal fit but it's your call.

Or just go with 53.94 which is the stock size...
..you are correct on that math...ooopps...
...which means that the pistons incrementally get bigger by... .01 mm = .0003937 inches...unmeasurable by hand..
bents
Posts
3282
Joined
12/31/2009
Location
CA
Fantasy
710th
5/18/2016 2:40pm
Peely, I get that you were joking. Been on here long enough to recognize that. I'm just trying to get to the bottom of buying the right piston for the bike, and I didn't know till now that there was a cylinder A and B or that there were different size stock pistons for a 2002. I just want to have a fresh top end for the summer!! And I don't want to make the mistake of putting the wrong piston in, now matter how miniscule the difference.

Thanks for the advice. I think I will go stock OEM at 53.94

Post a reply to: 2002 CR125 Piston replacement question

The Latest