RE: MOKI RADIAL Care and Maintenence
Hi fellow radial addicts, and thanks Scott for launching this.
Here is what I have gleaned after 3 years running two 250's (one on a 3W Bearcat with a 30x18 Menz prop, one on a 1/3 scale B-USA Stearman with a 32x12 prop):
1) Cooling. Stearman was easy .. hanging in the breeze. In the Bearcat, I put "pie-shaped" deflectors in between all the cylinders to force all airflow over the fins. The cowl on the B'Cat is tight enough on the outside dimension that no air block was needed there. I have posted pics of the install on other RCU threads, when I have some time, I'll repost here.
2) Lubrication. Each day, light machine oil on the rockers. A few times a season, lubriplate on the pushrod ends.
3) The air pump. Always use a clear 3mm festo tube to the carb so you can check for grease residue. That will stop the motor, as no pressure pulses reach the pump in the carb. I expect a little grease to be extruded from the breather hole in the back of the pump on each flight. When this stops, it means it is time to add some more grease. I use high-temp disk brake lube. The little pump simply unscrews with a good quality open-end wrench on the flats on its head, and the lube can be put in with a hypo. If you keep flying after the grease stops coming out, that's when you seem to get grease vapor plating out on the clear tube, which eventually will clog it. I keep 2-3 spare pre-cut tubes with me in my radial tool kit.
4) Ignition battery. I have always run my two motors on 4.8V. I too hear about some that "like" 4.8 and some that "like" 6.0V. It is my belief that to run well the ignition needs a VERY low impedance voltage source. I had a lot of problems at first with ignition packs that were too small (e.g. 2400 mah .. and good Sanyo cells too). I ended up going to 4400 or 5000 mah NiCd or very good quality NiMh with 5 milliohms or less output impedance. The flights don't take too much total current (maybe 400-500 maH to recharge) so it's really the low impedance that is needed .. not the absolute capacity. My belief is that it is possible that the people using 6V are compensating for batts that are high impedance or too small... but that is only a guess.
5) Oil. On Mike Dooley's recommendation, I mostly run the motors with Yamalube mixed 30:1. I also experimented with the 50:1 Amsoil mixed at 40:1. I found the engine ran smoother and cleaner on the leaner oil mix (that black gunk that comes out the exhaust with the Yamalube is some nasty stuff!).
6) Spark plugs. They seem to get quite black and ugly in 10-20 flights. Not sure if this is an over-oil problem (see #5 above), or a too-rich mix, or perhaps that the engine runs cooler than most of the gas two strokes I have. This is based only on temp gun readings on the ground, where the 250s seems to be in the 215-225C range, where most of my other gassers run hotter than that. I would love to know more about this. I often change the plugs just because they look so awful, even though the motor still runs ok.
7) Exhaust port nuts. Yep, they get loose. I lightly tighten them each flying session while I have the cowl off to do lubrication. Heard too many stories of stripping the threads so I tighten them very gently...
That's what I can think of for now .. thanks to all for posting such great stuff here!
Dave
8)