fr5-300 oil vs fr7-420
 

Bax,
I have a couple of FR5-300s, running fine at specified oil level (18%). Now I read that the FR7-420 specifies a max of 10% oil. I have replaced all bearings in one of my FR5s, and again based on reviews, they dont seem have any significant bearing differences with the FR7 - ie ball races on crank and cam idler, needles on the big end and cams. This makes me wonder why the FR7 needs so much less oil than the FR5. LESS OIL = MORE METHANOL = MORE POWER to my way of thinking.
Can you shed any light on this please?
thanks
jp

RE: fr5-300 oil vs fr7-420
 

Likely, it's because internal pressures at the metal-to-metal interfaces are lower, so the amount of oil doesn't have to be as high. OS knows what they're doing. Just make sure you use a good after-run product at the end of each flying day to get the steel parts well coated to prevent corrosion.

RE: fr5-300 oil vs fr7-420
 

Bax,
Thanks. Not something I am going to experiment with.

I always pump some red ATF in through the breather and turn it over, and plug the breather, before putting away after flying.

As for OS knowing what they are doing...talk to FS120SP owners with failed regulators and no solution even when they were current models, or seemingly hiding the solution to failed regulator covers on FS120-P Surpass engines. We only found the solution to this last problem by knowing somebody who worked at the importer, and gave us the part no for the modified cover.

jp