chistech

Hey Mike,
Thanks, I didn't even realize it's been a year. One thing I didn't mention is that although I live in the North East, I fly year round. Luckily I have a brother and a buddy who also flies with me. Even when its real cold we still will fly. I don't use ARO in my engines because they do usually go more than 2 weeks without running. I have recently been building more warbirds for myself so the time spans will get longer between flights for some models so I will start using it now. The reason I stated this is I would still use the plain steel bearings over the Stainless ones. Steel is harder than stainless and a bearing fails when the balls get out of round, the races get grooved, or things get pitted. Yes, I know that there are other types of failures but some sort of wear is usually what starts the process to failure. Load on a bearing is what initially starts wear. A harder, rounder ball will perform longer. A race that retains it's proper groove again will last longer. If a engine is maintained correctly or used often the steel bearings should be fine. Again, don't rule out excessive heat. Cooking a fuels lubricant to the bearing surfaces then putting the model away for a while will cause the balls to load up with crap. When you go to restart a ball could stick and not roll causing the chain of events that can lead to failure. A ball that locks up is what usually causes the cage to detonate.These are some possibles and by no means "God's word" to bearings going so I'm not looking for arguements. I again, am just going by my own experiences. I too have never had the need to put bearings in any of the engines I bought new but I like buying used engines, especially 4st's and rebuilding them. It is funny that this post was started on a Saito issue. A customer that I am building a P40 for called me today to say that he has a issue with a S100 that has bad bearings. It seems they were replaced about a year ago and are now gone again. The bearings were originally replaced with factory bearings. I wonder if the 100's have a problem with something being "out of spec". Things are made all the time that get recalled or replaced because they got out the door with a problem. Just thought of something. I know of a guy in another club who was over tightening his prop nut so much that it caused too much constriction on the crank shaft bearings. Yes, it can be done. Tighten the prop tight enough and you can enlarge the hole in the ALUMINUM thrust washer ever so slightly and every time you sock it up it will get tighter as an assembly. The rear bearing in a model engine, although used as a thrust bearing, is really a radial bearing. Making the whole assembly tighter will put the load of the balls up against the forward facing edge of the outer and inner races. This allows less bearing surface contact between the balls and the races making the load rating of the bearing less. I.E. bearings are rated like anything else to do a certain job if used in the proper manner. A radial bearing that is being used as a thrust bearing is already at a deficiency never mind when a excessive side load is applied. If tight enough, the lubricant will not be able to get between the balls and the races or actually, be forced out because there is just no room for it. A soft Stainless Steel bearing will not tolerate this. A model engine crank should have some back and forth "play". Not a lot, but some. If it doesn't you will eventually have a problem. When I assemble a engine I will always put a prop on the crank without attaching the piston and and check to see how it spins. I have found a brand new bearing that was bad this way. Because it is new, don't assume it is ok. I hope I didn't start people thinking they have the wrong rear bearing in their engines. If people don't understand the difference between bearings, our standard type ball bearings in our engines are designed to take a radial load. ( spinning shaft ) a thrust bearing takes a axial load ( load is from the side ). The crankshafts in our engines are kept in the motor by applying a side load to a radial bearing. Because of the size of the bearing compared to the size of the axial load we get away with the improper application of the radial bearing. In a perfect world there would be both a axial bearing at the immediate rear of the crank to handle the side load and then a radial bearing right next to it to handle the spinning load. There are large bearings that do double duty in this way. A good example of a double duty bearing would be a tapered roller bearing like in a axle of a trailer or car. It takes a radial and a axial load. Again, even on a vehicle, the bearing is allowed to have some "play" by not tightening the axle nut too tight.