Motor Experts Help 03 CR125


4 replies to this topic
  • tat2guy

Posted October 18, 2010 - 07:46 AM

#1

Going through and reading all the post have been very helpful, BUT I want to throw something out there.

1)I've read in a number of places that an RM125 piston with head mod is a killer upgrade.

2)Also that a 134cc BBK is great.

OK here it is...

But what if you did the BBK and used the RM125 (56mm) piston in the two combined mods????

And to those who will post get a bigger bike not to worry, this is one of 4 bikes and by far the most fun.

:ride:Thanks Jay:worthy:

  • harrperf

Posted October 18, 2010 - 10:56 AM

#2

This is our personal killer set up:

We build the honda using a yz125 piston from an 04 engine. Be it a 125 or a 134.

The piston ring locating pin is on centerline which allows better use after porting of rear/secondary transfers and maintains an intake window for excellent piston crown cooling.

Intake window is not NEEDED and the GP style pistons sold work well too - but if your keeping stock bore - tough to beat an OEM yamaha piston for price AND how well it works.

The honda wiseco GP piston works fine too - as it also locates ring pin on centerline.

  • tat2guy

Posted October 18, 2010 - 12:53 PM

#3

Is the YZ piston taller than the RM piston??? From what I read the piston height difference from the CR to the RM drastically boost low end. Would that be correct??? I read this in one of Eric Gorrs books....

  • nesc103y

Posted October 18, 2010 - 12:59 PM

#4

This is our personal killer set up:

We build the honda using a yz125 piston from an 04 engine. Be it a 125 or a 134.

The piston ring locating pin is on centerline which allows better use after porting of rear/secondary transfers and maintains an intake window for excellent piston crown cooling.

Intake window is not NEEDED and the GP style pistons sold work well too - but if your keeping stock bore - tough to beat an OEM yamaha piston for price AND how well it works.

The honda wiseco GP piston works fine too - as it also locates ring pin on centerline.



So are you saying the 04 YZ125 piston is a bolt on performance increase?
Can you elaborate? What is it with the Yam piston which makes it better?

Thanks in advance

  • harrperf

Posted October 18, 2010 - 03:16 PM

#5

It's not a bolt on power adder.

The RM piston will alter the timing heights considerably - giving it more bottom with an equal loss of top. It would also require a head mod to even fit - as delivered it will hit the head.

I use it because it's cheap and timing height is damn near the same - AND most importantly the ring locating pin is in the center of the boost port - allowing wider rear transfers giving more area of port without altering timing - allowing an exhaust set up that does not get too high in the timing numbers.

in our ideal set up - we also shave a tad off the base of cylinder to get squish where we want it with the yz piston.





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