1994 CR125 with Suzuki piston.

[Robin13]

I need to replace the cr's piston. The cilinder isn't modified except the ports edges are smoothed. The piston is from a Suzuki. The top has been machined to shorten it. The shop that did the tuning does not exist anymore, so I can't ask them for a new one or ask if a stock piston will work or not. The suzuki piston doesn't have the window in the skirt the stock honda piston does. So does anybody know if this is known tuning method? And what piston will also work. Currently the bike is almost only topend wich comes in really hard, maybe the window in the stock piston will give it some more low end? Any other tips are apriciated. I've tried to find threads on this, but failed to find any.

 

[marcusgunby]

Ive heard of this when using a long rod to change the rod ratio-not sure of the piston year however.

 

[NO HAND]

I read about this on Eric Gorr's website, or in his book- I don't remember. But, I know it was a common mod for cr125 to go with the rm125 piston, only the squish clearance had to be adjusted to run with the suzuki piston. You will now need to run the rm 125 piston in your bike, because the head clearance has been changed to run on the suzuki piston-I presume. I read this info in 2000-2001 so I would believe a piston for the rm125 2000 should be just right. I know the cr125 piston was the same from 1992 up til recently, but you're not gonna need the cr piston anyway. I'll get back to you on the advantages of the rm setup in your bike.

 

[NO HAND]

The 2000 RM125 piston is 1.5mm shorter on the timing height. This piston will advance the port timing and increase the duration of the transfer and exhaust phases. The ring centering pins on both pistons are directly on center with the rear boost port. That enables the rear transfer ports to be widened even further for more overrev.

RM Piston, Stock Exhaust
Turndown the gasket surface 1.25mm up to the squishband so the entire 54mm of combustion chamber protrudes past the gasket surface. The RM piston has a shorter timing height and this mod will compensate for the distance between the piston and head.

 

[Robin13]

Thanks alot NO HAND. Do you maybe know something about the piston being a dome shape? The piston that came out of my cr has a dome. There are no markings on the top of the piston, and I can remember the guy from the shop telling me he machined a bit from the top and that it was an RM piston.The RM piston already has a dome right? The pistons been in my bike since about '98 and was tuned in '94. On the wiseco website there are 2 versions you can choose from: '89-'99 (641M05400) and 90-03 (764M05400). Can you maybe say wich one I need. Than I can get a machineshop to machine it to the right size. I'll try to get some pics of the piston. Thanks agian.

 

[NO HAND]

Your piston has a dome? I'm surprised because I know your bike had a flat top piston as it was stock, and the 2000 rm125 piston was flat top also. I don't know if a flat top piston can be machined to become a domed piston, I'm scared it would become too weak at the crown. I'm puzzled. Does anyone here on DRN knows if the piston model from 89-99 was a domed piston?

 

[Robin13]

If the stock piston is domed, would it not be better to just use a thicker cilinder base gasket to get the clearence? (I meant the stock suzuki piston)

 

[Robin13]

Pics of the piston, first one with dimensions:

http://picserver.org/view_image.php/5Q9C8731CA4M
http://picserver.org/view_image.php/JI17DJ3A4U47
http://picserver.org/view_image.php/8K5R02K3HUM9
http://picserver.org/view_image.php/TK83AY070196

If this is a suzuki piston, could somebody measure the piston to see what the differences are? Thanks

 

[marcusgunby]

I would take it to a suzuki dealer and let him try to match it up so you know what year you will need.

 

[georgieboy]

Robin, make a pic of the head. Maybe the squish is specially prepped for the dome piston. I can remember that the squish was slightly tapered. And measure the head gasket to give a squish height measurement. The prepped head cld ask for a dome piston.
edit: Robin and I know each other, but we both lack experience ;) . My limited knowledge is more off the project from hell, to use Marcus's words. :yikes: