Case solved! I got a call from Ron at RB Designs today who said the head I sent him has already been machined... that the squish has been reduced BUT the combustion chamber and volume was NOT modified proportional to the reduced squish/increased compression! I had no idea, but a previous owner must have either done it himself or sent it away to a machinist (not RB) who did a half ass job. He said he's 99% sure that the shoddy head work is to blame for my jetting woes and deformed piston due to mismatched combustion chamber volume to VERY high compression. Additional details on the topic are above my level of knowledge so feel free to further explain things, but it's nice to know the story of the mangled 300 piston!
RB said they'll do their very best to calculate the ideal combustion chamber dimensions and complete the machining job per their successful specifications. Looking forward to reassembly and takin' er out for a rip!
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Originally Posted by Moto7man
Just an idea. Did you have someone measure your cylinder bore? You may need to go to a B or C piston to tighten things up a bit.
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Moto7man, this is a good question. Surprisingly, I measured the bore with a friend's help and fancy bore gauge AND my local GasGas dealer matched the "A" piston to my cylinder in their shop. Both my friend and the GG dealer said that either I started with a slightly smaller cylinder and piston (both are stamped "A") or despite all the dome and skirt damage shown on the piston the cylinder has sustained a nearly immeasurable amount of wear. Odd, I know, but the GG dealer adamantly recommended installation of another "A" piston because a "B" had the potential to cold seize. So... "A" it is...