noisy engine
 

I have a OS 46 LA engine in one of my trainers and I noticed a knocking noise coming from it whenever I'm below 1/2 throttle. I asked someone at the field about it and he said the bushing was worn. I checked the OS site but I don't see a listing for the bushing. Does it come with the crank?? Is it the thrust washer?? Any help would be helpful[8D]

RE: noisy engine
 

Just as a note here, my OS 75's (both of them) have what sounds like a knock when flying about half throttle. I'm not sure what it is, but they both did they were new.

CGr

RE: noisy engine
 

In the O.S. LA-series of engines, the crankshaft rotates inside a bronze bushing. As a result, the crankshaft must be free to move fore and aft. If it was "captured" there would be too much friction against the forward and aftward ends of the bushing, and the engine would seize from the high heat generated by that friction. As a result of the "floating" action of the crankcase, it will tend to move fore and aft when the power settings are less than full. The fore and aft movement will cause the rear of the crankshaft to tap the aft end of the bushing, and the drive washer to tap the forward end of the bushing. This causes a tapping/rattling sound. It's absolutely normal. You just have to live with it. You can reduce the sound by using a fuel with a 20%-25% oil content that contains at least 50% castor oil in the oil mix. Castor oil will provide more cushioning than synthetic fuels, and will reduce the noise.

ANY BRAND of engine that has a bushing-supported crankshaft will make that noise.

For the O.S. .75 AX, we have found that larger glow engines, starting around the .75-size, will make a kind of "popping" sound. Some people have compared it to a "metal-to-metal" noise. We've seen this in engines of different sizes and different brands. The only conclusion we can come to is that there is some kind of exhaust noise happening. We've never found any evidence of abnormal rubbing or other type of metal-to-metal contact. All the engines we've inspected that made such a noise showed absolutely nothing wrong when they were disassembled and inspected. We can only conclude that it's an exhaust note, possibly caused by unburned fuel being exhausted from the engine and then burning in the muffler, or just outside of the engine's exhaust stack.

RE: noisy engine
 

I too have the 46la and it has always made that noise. I think it is normal for the la. Just replaced it with an ax. Much much better so far.

RE: noisy engine
 

Thank you for the answers. I'll just keep having fun flying:)