Roadracing 125cc 2-stroke piston choice

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Nov 17, 2002
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#2
Forged = more durability

However, make sure you warm the bike up thoroughly before ANY high rpm running both cast and forged, but especially with a forged piston.

Doesn't matter, two stroke....fourstroke..Always warm it up before high revs and if you've got a forged piston this is even more critical....MX bikes, roadrace bikes...It doesn't matter.
 
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#3
Some modern cast pistons are showing great wear resistance and good strength. This in conjunction with the ability to hold tight tolerances (for better power) may make a quality cast piston a good choice. But, that does not make all cast pistons good ones. ART has made quality pistons for years. Find out what others are using and the results they have.

Chris
 
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#4
If you don't want to replace pistons or rings all the time, which many top kart racers do, there is no doubt what to use. The RS 125 Honda piston is the only way to go. Its ring lasts even with wide exhaust ports and loose fit. Some people use Vertex or Wiseco with good results but change them every 2 hours. Cost doesn't matter to some people, or they get them very cheaply. I've had customers go 6 hours with RS pistons on engines highly tuned enough to win Nationals on large tracks. My opinion, cast is the only way to go!
Wes Gilbert
Boyesen Precision Porting
PS. I have them in stock
 
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#6
Your cylinder would have to be rotated .060" at studs clockwise so ring pin would be more centered between left rear transfer and boost port. The head would have to be recut slightly also
Wes Gilbert
 

WWR

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#7
Fastwes,
if you use the RS piston with the pin centered at the back of the piston, you wouldnt need to rotate the cylinder. The ring gap would be in the center of the rear boost port, which actually works quite well.
 

WWR

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#9
Maybe. Not really sure. I just know that the HARC PRO shop down the street here offers these different pistons with the pin centered. Havent asked the details, there is a bit of a language barrier. They may just be a piston offered and designed by HARC PRO.

The RS pistons also do not have the holes cut into the sides of the pistons like most of the dirtbike pistons. Not sure what that does. Eric told me once, but I forgot.
 
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#10
The HONDA RS 125 pistons I use are 1995-2002(pt # 13100-nx4-780) and have the pin offset between the boost and left rear transfer ports. The 03 is the same I believe. WISECO RS pistons are pinned in center. The HONDA pistons are cast, WISECO are forged.
Wes Gilbert
Boyesen Precision Porting