My pistons are modified before installation,I have some bad pictures of the pistons,I am trying to get better shots I hope later I will be sucessfull.
The point of the flat upper exhaust interests me, although I know it is not flat I will put more curve on it. Good Point.
My port shape has been the same for the past two years using Zenoah maybe the Rcmk can't handle it.

I read a few about the backside Mods to lighten by removing material --- some take too much from rear of pin area (back side) and make it weak - did see a few that may have issues because of aamount of material removed.

Just a thought

No material was removed from the upper inside of the piston.

Post some MACRO pictures of piston / exhaust roof profiles
Really thinking an impact issue from rings end gap against index pin due to port shape ???

here are the pictures

here are the pictures


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Your pictures aren't accessable from here.

I can't see pictures either. You said your pistons are modified and no material has been removed from the inside. Just curious if you are turning down the upper part of the side of the piston that is commonly done on Zen pistons? RCMK pistons are tapered and turning them down should not be done! If it is done could it promote ring snagging as Scott described?

Today I used a stock piston,reshaped the upper exhaust port to be symmetrical and I tapered the upper port to an arc that will eliminate ring lock.
I ran four liters of gas/oil mix at 12:1 mixture gradually increasing from high idle at the end of this break-in I made one attempt to accelerate to full throttle, it failed at the first attempt the pin broke, the ring rotated and one end stuck into the exhaust port destroying the ring groove. I removed the ring carefully and saw the broken end of the pin behind the ring.
I came home and rebuilt the engine with a Zenoah piston and started it up. Not caring about the consequences I revved the newly built engine to full throttle. Absolutely no problem. I am convinced that the pin is at fault.
I have placed an order for a QD29 and I have given up on the RCMK K30 piston until they install an appropriate pin.
In the mean time while I await on the QD I will race this engine.
Thank you All for your suggestions, all were pertinent but as one of you guys said there is a production issue, people will learn of it when they try to get these engines to run like mine,
By the way the three new pistons that I bought one pin was located to the upper side of the port, one was in the middle the the other was to the lower end of the port.
How consistent is that ?

I would be in contact DIRECTLY with Mr.Park at the RCMK factory.

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