I have finally had time to balance the crankshaft an my 91 FX and removed as much material from the conrod pin area on the crankshaft and also removed material from the conrod in an effort to smooth this motor out at idle and high speed. When removing the crankshaft it was so tight in the bearings that I had to press the crank out with a bearing press which is way to tight so I chucked the crank up in my lahte and used 280 grit wet/dry sand paper with oil to try to get the OD of the crank bearing surfaces down so it would slip in the bearings with very little effort. I was successful in getting some of the vibration out of the motor but it is still way heavy on the con rod side and there is just not enough counter weight on the counter balance to help balance out the weight of the conrod, piston, and wrist pin so I got it as good as I could. I was also able to get the crankshaft to slide into the bearings so there is a few thousands of end play but not enough.
I just finished running the motor on a test stand with a MAS 13/6 prop and Omega 15% fuel...there is no bubbles in the line from the carb to the remote needle but I never had that problem when it was in the plane. I got the engine adjusted good but I think 15% may be to much nitro because even at a very rich setting the motor runs very hot.
I don't think the carb is the problem nor was it over proped to cause the heat problem but there is still alot of high speed vibration. I was not able to really check for idle vibration because it was on a solid test stand.
My biggest complaint about the motor is vibration and heat...I also think maybe a bigger carb might help. I don't see where a pump is going to help me much because I am not seeing a lean out problem but I am not ready to throw in the towell on this motor yet. I have a Super Tiger 90 that is as we all know in the same size case as the ST .61 and somehow ST did not suffer any of the problems we are seeing in the OS.
This is the first glow motor I have ever had that the crank was so tight in the bearings that it had to be pressed out and it is a problem that I have never seen in an os engine until now which leads me to beleive OS is having to scale back on QC to keep the cost down. Any comments about the heat and vibration would be appreciated.