ORIGINAL: Kweasel
Look at the underside of an SFN/RFN piston, you will find that the aft pin boss has been relieved. This allows the rod to slide aft and clear the crankpin, FSR/VF pistons do not have this feature. It is often difficult to get the rod to slide back on used engines due to burned oil residue on the wristpin. My experience with carbs has shown that a 7D/DV with a .355" venturi on a .61 is the upper limit for good fuel draw, and thats at 14000+ rpm. The 6B carb has a .385" hole with a thin spraybar making it too big (depending on your standards) for most airplane applications, unless a pump is employed. Helicopters can use larger carbs because they turn more rpm and have fuel tanks mounted very close to the carb. For the most power, try to find an older .65DF cylinder/piston and head, they drop in .61 cases and are awsome with a pipe.
Got it. Thanks for the great info. I now see what you are talking about.
On the VF piston in a RF case you can put the conrod on the crankpin first, without the piston on it.
Next put a piston pin clip on the forward pin boss of the piston.
Place the piston and liner in the case with the piston sticking out the bottom of the liner so the pin boss is exposed.
Line up the aft pin boss of the piston with the rear exhaust port.
Line up the conrod with the pin boss.
Slide the piston pin in through the aft pin boss through the conrod.
Place pin clip on.
Slide liner the rest of the way down until it seats with guide pin.
I figured this out for the same reason you mentioned above about the burned oil residue on the pin. I didn't want to have to pry off the conrod from the crankpin possible ruining it (the conrod). So pulled the liner out until it past the exhaust port to gain access to the pin boss. Applied a little oil and heat from a heat gun. Used a small easyout on the piston pin and kept turning it to get it out.
Worked great and no damage to the bottom boss on the conrod. This probably why i didn't run into the the problem you were mentioning on the VF to RF case swap.
I was able to get a FSR piston and liner into a SF case. In order to get it on the crankpin I had to heat up the the conrod with a heat gun through the rear of the the case with out the liner. It finally went on. I had to do the same to get it off. Someone made this suggestion here in one of the forums about how to get the SF conrod off the SF crankpin. So I figure this must be SOP for getting the conrod off of single piece cases (no seperate front housing).
Bryan