We assembled our set more or less two months ago in one almost new stock Chinese ST 51, that was only bench ran for a few times before installing the new BG ABC.
To install the new set, after taking out the old, and installing the new piston and rod in the crank, what was easy to do, we had to heat the case with a small torch and freeze the new liner in the refrigerator before throwing it in the case. This way, it entered easily, but maybe this wasn’t the best choice to do the job, because when it will be necessary to disassemble the engine in the future, we can have difficulty to take it out. Another way was to grind/lap the internal part of the case or the external of the liner and install the liner without heating and freezing the parts. This would require much more work now, but maybe with less difficulty in the future.
Another thing is that the piston and liner, even before installing the set in the engine, were too tight with each other, but we choose, for obvious reasons, not to grind any of them and leave this job for the brake in sessions, on the bench.
We bench ran it with one Master Airscrew 12X5, nylon propeller, glow with 5% nitro and 22% oil 50 to 50. It always started very easy, but In the firsts runs didn’t pass 8500 rpm (four cycles), if we tried to pass this rotation, closing the needle, it heated and died. This was caused by the very tight fit between piston and liner. We changed the prop to one APC 13X4 Sport and introduced one more shim in the head. After almost 1 liter of fuel and many runs of 2 min it was hitting higher speeds. After 0.5 liter more it was hitting 10500 rpm in a very constant 2 cycles for 30 s. It wasn’t totally broken in, but we considered this enough to install in a plane.
We installed it in an ARF Pathfinder that my son (35 y) was using to train the F2B gamma maneuvers. The plane was with an O.S. 46 LA, before, but we were looking for a little more power and torque, and we got this with the substitution, using the same prop of the LA 46, a Master 12X5, nylon, and the same fuel that we used to bench run.
It always started very easily, in the first or second flip when cold and a little more flips when hot, with very constant and reliable runs with a good 4-2-4 if well carbureted. With this prop we were launching in a fast 4 C with 9200 rpm. It spends a little more fuel than the LA. We are using a 5 Oz, uniflow, pressurized tank for a little more than 6 ½ min flights. The muffler is a very light (28 g) T&L for ST 51.
Now we are with almost 50 flights with it in the plane, very reliable and strong in all gamma maneuvers. We recently changed the prop to a 12X6, nylon, MA. With this prop we are launching with a fast 4 C in 8400 rpm. Next step will be to change to a wood 12X6 MA, more light than the firsts.
However, we think that the piston is still a little tighter than usual and don’t know if this wouldn’t force excessively the rod with the time or if this only means that the set will have a long duration life. The truth is that until now we are very happy with the set and engine.
Thanks to Brian. Luiz
Topic: Anybody running a B.G. ST51 P&L (Read 4897 times)