Rebuilding a modified Honda CR 125 and came across this issue….Bought a 2005 domed Honda OEM Piston (13110-KSR-730) as an economical replacement for the HRS piston. Found that locating pin for the ring on the 2005 piston is directly in line with one of the ports – so the ring gap will run directly thru the center of the port. Whereas on all my previous RS pistons, the ring gap is offset so that it runs in the bridge between the ports. Another way to describe is that (looking at the top of the piston) the 2005 ring gap is located at 6 oclock and the HRS piston’s ring gap is located at 7 oclock. I’m concerned that the 2005 piston setup will snag the ring in the port. Did I get an errant 2005 piston? Or is that normal to run the ring gap directly over a port when using the 2005? Obviously we can chamfer the port, but from everything I’ve read about rings, setting the gap over the port is a fundamental no no. Can anyone shed some light on the 2005 setup please?
Geez, what happened to ekarting forums? 8 years ago, there would have been 10 different responses, and 30 ensuing arguments….Seriously, NOBODY else has run into this same issue?
is it in the same location as these two photos?
Swedetech quotes blueprinted/mod 1999 CR125 top end replacement as the same part number you posted.
Thank you Matt, I find the topic search feature here a bit fumbly at times. Good info on the squish info in that post as well. I’ve already made that adjustment with the gasket set. The piston I have is in fact the same as the picture you posted and the ring gap is indeed directly in line with the port. Also, rummaging thru my leftovers, I found a Vertex RS piston that also had the ring gap in the same location as the 2005 Honda OE. (it was seized in the piston of course, I hope that’s not a bad omen) However, all of the HRS all have the ring gap placed at 7 o’clock in the bridge. We’ll run the 05 piston and see how it works.
Sorry I took so long to respond, but you are correct. I had to track down an RS piston.
The RS piston has the ring gap at a bridge and the 2005 piston has it in the gap portion of the intake. That said, the 2005 ring gap looks to be supported pretty well by the bridges on each side and the gap perfectly in the center of the intake. I have run many of these 2005 pistons and I have never suffered a problem from the the ring gap.
This is the cool side of the piston. I would look for problems on the exhaust side,particularly the top of the exhaust bridge showing a little cracking. This will catch a ring in a New York second.
I have been told that drilling a couple of holes in the 2005 piston to cool that bridge won’t hurt(RS piston sports two tiny holes).
So, that being said, I haven’t seen a problem with the ring gap you describe.
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