Kx125 pistons

dannyb123
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dannyb123

Does anyone know a dead giveaway between kx125 1997 and 1998? And my main question, it seems 95 up untill 02 kx125 pistons are all pretty much the same sizes? Do they all fit? And one could choose a 95 kx125 B piston and it would be the same size of.. whatever.. 1999 A? For example? Are they interchangeable? I’m in China and I have a 97 or 98, supposedly 97, and there are only 99-00 pistons available.. any tips?

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dannyb123
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dannyb123 10/9/2023 7:12am
10/9/2023 7:12am

Simpler question, 97+98 dead giveaways? And are 95-02 pistons the same besides size (0.01-0.02 diff) ? Skirt length etc the same?

MxAddic
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MxAddic 10/9/2023 5:54pm
10/9/2023 5:54pm Edited Date/Time 10/10/2023 4:38am
MxAddic wrote:

http://catalogs.wps-inc.com/2023/offroad/

 

dannyb123 wrote:

Didn’t find any information there..

That is the listings for all the aftermarket pistons for the bike. I don't know what other information there is Your searching for the tooth fairy..

 

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Kidkawie
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Kidkawie 10/10/2023 2:05am
10/10/2023 2:05am

You mean you can't find one made in China?

Kidkawie
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Kidkawie 10/10/2023 3:27am
10/10/2023 3:27am

From what I read, 95-01 diameters and the wrist pin are the same,  but 98 got a 2mm shorter rod and added porting.

DJS721
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DJS721 10/10/2023 3:44am
10/10/2023 3:44am

The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome

The 1998 KX125 piston is also 29.5mm compression distance, and 15mm wrist pin, with the same dome shape

The large difference is the locating pins are different locations:

1995-1997 locating pin is 25deg from centerline to the right

1998 locating pin is 26deg to the left

So the locating pins are different locations due to the port positions in the cylinder

Also the 1998 piston includes a small boost port on the intake side of the piston, where the 1995-1997 does not

3
Kidkawie
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Kidkawie 10/10/2023 2:13pm
10/10/2023 2:13pm
DJS721 wrote:
The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome The 1998 KX125 piston is also 29.5mm compression distance...

The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome

The 1998 KX125 piston is also 29.5mm compression distance, and 15mm wrist pin, with the same dome shape

The large difference is the locating pins are different locations:

1995-1997 locating pin is 25deg from centerline to the right

1998 locating pin is 26deg to the left

So the locating pins are different locations due to the port positions in the cylinder

Also the 1998 piston includes a small boost port on the intake side of the piston, where the 1995-1997 does not

Same wrist pin location?

dannyb123
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dannyb123 10/10/2023 8:04pm
10/10/2023 8:04pm
DJS721 wrote:
The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome The 1998 KX125 piston is also 29.5mm compression distance...

The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome

The 1998 KX125 piston is also 29.5mm compression distance, and 15mm wrist pin, with the same dome shape

The large difference is the locating pins are different locations:

1995-1997 locating pin is 25deg from centerline to the right

1998 locating pin is 26deg to the left

So the locating pins are different locations due to the port positions in the cylinder

Also the 1998 piston includes a small boost port on the intake side of the piston, where the 1995-1997 does not

Does the locating pin difference matter? Would they be interchangeable? Thanks a lot for the reply by the way. I was looking for an expert! It seems that only a 99-00 piston is available. What about this piston? 
 

so to determine if it’s a 95-97 I can see if there’s a boost port on the intake side, for a 98, furthermore, I suppose it will affect performance a little bit, seeing as the piston corresponds with the porting.. problem is I’m unsure what I have, the engine seems to be a  97, since the engine numbers are 00 not 01.. but you never know, frankenstein bikes sometimes here.. and about Chinese piston, I once bought a cr250 chinese piston, and for a yz125 I bought it had one, and a cr, they don’t have the intake port holes, and the quality.. also skirt sizes etc were always off. I bought one and I never fit it seeing as it was so off with the oem. You’d say since most parts are made in china like pro circuit parts we’d be able to buy them.. but not really, PC protects their products VERY well. Same as a lot of other brands. The only thing we can freely buy are some crappy brake pads, very cheap chains and sprockets, levers etc. But they’re all not oem obv so.. only for backyard crosstracks imo (for anyone who’s curious). And the vforces here are like 10-15$ for those fake or sneaky over produced and sold locally? Anyway I fit 2-3 on my bikes they all gave me an airleak. But I did see vforces can leak, even the “real” ones, especially the old vforce 3. So idk.. 

 

so anyway, I got a 97 (probably) possibly a 98 (less likely) in simple words, they all fit but would affect performance, IF the clearance is ok, (99-00 might differ a MM from 95-97?) so I suppose I keep riding on with this 150 psi till I go back to Europe next holiday and buy an oem one I guess? Or should I bolt up that 99-00 piston? 
 

thanks for all replies, Danny.

 

dannyb123
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dannyb123 10/10/2023 8:09pm
10/10/2023 8:09pm

I’m trying to rebuild this kx125, but yeah I noticed that kx parts are.. rather rare. Honda parts are flooded here, as are bikes. Cr’s.. but these kx’s are a rarity here, in general. I already have 3 cr’s here so, time for a kx. I’ll try to post some pics once I get it all done. Am not going for a huge build or something, but it was 1300$, full pro circuit pipe, with pro circuit frameguards. Couldn’t resist! Also can’t buy fork springs and other springs so I’m gonna try to let them get refurbished here.. bad idea, I know. Anyway I’m curious for the result. I could also buy that 99-00 piston and let them resleeve the cylinder, would take a month. Does anyone recommend that? But they’ll 90% mess up any porting.. you have to be happy if they didn’t mess up the sleeve itself already.. so.. perhaps that nasty 150 psi is the choice for now..? Better than most second hand bikes I bought here anyway. Any advice is welcome 😁

TDC
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TDC 10/11/2023 6:48pm
10/11/2023 6:48pm

135 big-bore kit!

MxAddic
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MxAddic 10/11/2023 7:11pm
10/11/2023 7:11pm

If you know a good machinist you can make it work. Cut the piston/head and relocate the pins. GL!

DJS721
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DJS721 10/12/2023 3:53am
10/12/2023 3:53am Edited Date/Time 10/12/2023 3:54am
DJS721 wrote:
The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome The 1998 KX125 piston is also 29.5mm compression distance...

The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome

The 1998 KX125 piston is also 29.5mm compression distance, and 15mm wrist pin, with the same dome shape

The large difference is the locating pins are different locations:

1995-1997 locating pin is 25deg from centerline to the right

1998 locating pin is 26deg to the left

So the locating pins are different locations due to the port positions in the cylinder

Also the 1998 piston includes a small boost port on the intake side of the piston, where the 1995-1997 does not

dannyb123 wrote:
Does the locating pin difference matter? Would they be interchangeable? Thanks a lot for the reply by the way. I was looking for an expert! It...

Does the locating pin difference matter? Would they be interchangeable? Thanks a lot for the reply by the way. I was looking for an expert! It seems that only a 99-00 piston is available. What about this piston? 
 

so to determine if it’s a 95-97 I can see if there’s a boost port on the intake side, for a 98, furthermore, I suppose it will affect performance a little bit, seeing as the piston corresponds with the porting.. problem is I’m unsure what I have, the engine seems to be a  97, since the engine numbers are 00 not 01.. but you never know, frankenstein bikes sometimes here.. and about Chinese piston, I once bought a cr250 chinese piston, and for a yz125 I bought it had one, and a cr, they don’t have the intake port holes, and the quality.. also skirt sizes etc were always off. I bought one and I never fit it seeing as it was so off with the oem. You’d say since most parts are made in china like pro circuit parts we’d be able to buy them.. but not really, PC protects their products VERY well. Same as a lot of other brands. The only thing we can freely buy are some crappy brake pads, very cheap chains and sprockets, levers etc. But they’re all not oem obv so.. only for backyard crosstracks imo (for anyone who’s curious). And the vforces here are like 10-15$ for those fake or sneaky over produced and sold locally? Anyway I fit 2-3 on my bikes they all gave me an airleak. But I did see vforces can leak, even the “real” ones, especially the old vforce 3. So idk.. 

 

so anyway, I got a 97 (probably) possibly a 98 (less likely) in simple words, they all fit but would affect performance, IF the clearance is ok, (99-00 might differ a MM from 95-97?) so I suppose I keep riding on with this 150 psi till I go back to Europe next holiday and buy an oem one I guess? Or should I bolt up that 99-00 piston? 
 

thanks for all replies, Danny.

 

Here are the dimensions for the 1999-2000 piston:

Compression distance 29.3mm, locating pin is 28deg right, and the crown is 1.1mm tall and round, with a 15mm piston pin

Therfore, the 1999-2000 piston is .2mm shorter that the 1995-1998 pistons.

The locating pin locations are key to the port locations in the cylinder, so whether the other pistons will fit is really something you have to measure and check. It the locating pin ends up in a port, then this is not going to work.

Otherwise, you should find the right piston for your model year, and not risk causing damage. Some performance shops are able to determine which pistons could be interchanged, but they always have detailed cylinder information to do this.

Regaridng piston size (diameter), you will need to measure the cylinder bore and then select the right graded piston size (A,B, or C) for your specific cylinder condition. All of the KX125's of this generation are a 54.0mm base nominal bore size from new, and then over time will wear, and the piston size can be selected for the cylinder condition.  

2
INeedaNewUsername 10/12/2023 12:40pm
10/12/2023 12:40pm
DJS721 wrote:
The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome The 1998 KX125 piston is also 29.5mm compression distance...

The 1995-1997 KX125 piston is 29.5mm compression distance, and 15mm wrist pin, with a 1mm round dome

The 1998 KX125 piston is also 29.5mm compression distance, and 15mm wrist pin, with the same dome shape

The large difference is the locating pins are different locations:

1995-1997 locating pin is 25deg from centerline to the right

1998 locating pin is 26deg to the left

So the locating pins are different locations due to the port positions in the cylinder

Also the 1998 piston includes a small boost port on the intake side of the piston, where the 1995-1997 does not

dannyb123 wrote:
Does the locating pin difference matter? Would they be interchangeable? Thanks a lot for the reply by the way. I was looking for an expert! It...

Does the locating pin difference matter? Would they be interchangeable? Thanks a lot for the reply by the way. I was looking for an expert! It seems that only a 99-00 piston is available. What about this piston? 
 

so to determine if it’s a 95-97 I can see if there’s a boost port on the intake side, for a 98, furthermore, I suppose it will affect performance a little bit, seeing as the piston corresponds with the porting.. problem is I’m unsure what I have, the engine seems to be a  97, since the engine numbers are 00 not 01.. but you never know, frankenstein bikes sometimes here.. and about Chinese piston, I once bought a cr250 chinese piston, and for a yz125 I bought it had one, and a cr, they don’t have the intake port holes, and the quality.. also skirt sizes etc were always off. I bought one and I never fit it seeing as it was so off with the oem. You’d say since most parts are made in china like pro circuit parts we’d be able to buy them.. but not really, PC protects their products VERY well. Same as a lot of other brands. The only thing we can freely buy are some crappy brake pads, very cheap chains and sprockets, levers etc. But they’re all not oem obv so.. only for backyard crosstracks imo (for anyone who’s curious). And the vforces here are like 10-15$ for those fake or sneaky over produced and sold locally? Anyway I fit 2-3 on my bikes they all gave me an airleak. But I did see vforces can leak, even the “real” ones, especially the old vforce 3. So idk.. 

 

so anyway, I got a 97 (probably) possibly a 98 (less likely) in simple words, they all fit but would affect performance, IF the clearance is ok, (99-00 might differ a MM from 95-97?) so I suppose I keep riding on with this 150 psi till I go back to Europe next holiday and buy an oem one I guess? Or should I bolt up that 99-00 piston? 
 

thanks for all replies, Danny.

 

DJS721 wrote:
Here are the dimensions for the 1999-2000 piston: Compression distance 29.3mm, locating pin is 28deg right, and the crown is 1.1mm tall and round, with a...

Here are the dimensions for the 1999-2000 piston:

Compression distance 29.3mm, locating pin is 28deg right, and the crown is 1.1mm tall and round, with a 15mm piston pin

Therfore, the 1999-2000 piston is .2mm shorter that the 1995-1998 pistons.

The locating pin locations are key to the port locations in the cylinder, so whether the other pistons will fit is really something you have to measure and check. It the locating pin ends up in a port, then this is not going to work.

Otherwise, you should find the right piston for your model year, and not risk causing damage. Some performance shops are able to determine which pistons could be interchanged, but they always have detailed cylinder information to do this.

Regaridng piston size (diameter), you will need to measure the cylinder bore and then select the right graded piston size (A,B, or C) for your specific cylinder condition. All of the KX125's of this generation are a 54.0mm base nominal bore size from new, and then over time will wear, and the piston size can be selected for the cylinder condition.  

Damn, that is next level info. 

TDC
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TDC 10/16/2023 10:04am
10/16/2023 10:04am

Anybody know about a flat top piston set-up as being the shite?

I had a Tuner tell me he could get me good power, but didn't bight, bc I didn't want to spend any extra money. Besides, I wanted to see how my STIC carb improves power using stawk specs. YAT

MxAddic
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MxAddic 10/16/2023 10:15am
10/16/2023 10:15am
TDC wrote:
Anybody know about a flat top piston set-up as being the shite? I had a Tuner tell me he could get me good power, but didn't...

Anybody know about a flat top piston set-up as being the shite?

I had a Tuner tell me he could get me good power, but didn't bight, bc I didn't want to spend any extra money. Besides, I wanted to see how my STIC carb improves power using stawk specs. YAT

That is the hot set-up for the 250 and 125 Kawi. You have to re-cut the head and run race gas.

1
dannyb123
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dannyb123 10/19/2023 3:15am
10/19/2023 3:15am

Thanks for all the replies and all knowledge shared. I’d rather not take the risk I guess, since I’m spending a lot and re-doing the whole bike. Might post a pic when it’s done! I’ll wait for a 98 piston, and perhaps redo the cylinder by that time. For now if the clearance allows I’ll just go for a ring (which is available)

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