After reading around the forum and elsewhere, I keep seeing mention of bearings and rings being changed in engines used for pattern flying. I have not heard about this with other types of flying. Can someone explain what its about? Do they wear out that fast?


I always have heard talk about this or that engine has several years of flying or hundreds or thousands of flights without doing anything to it (non pattern flying).

Many 2 cycle engines are sold with plain steel bearings instead of using stainless steel. The reason that I hear the most is that stainless steel is softer and doesn't make for as good a material for bearings. The problem is, regular steel bearings tend to corrode quickly in glow fuel applications. There are many favorite ways of tryign to prevent this using different types of after run oil etc., but I don't have much luck with this. If you live in a very humid climate and store airplanes in the basement like I do, you might have as much trouble too. If you are in a drier climate and don't have to store in a damp place, then you might get much better results.

Piston rings will eventually need replacement, but with good care in breaking in, running without setting the engine too lean and most of all, not running with corroded bearings, they should last many hundreds of flights. If you let the bearings get rusty, that stuff creates a polishing rouge when mixed with fuel and it just wears away at the piston, ring and cylinder liner (mostly the ring suffers).

use cool power fuel, den u wont need after run oil....

Not true. Alcohol attracts water and your bearings will rust even if you use cool power.

Bearing corrosion is a controversial subject, some peaple seem to get a lot of it and others say they don't. I use a lot of afterrun oil and still experience it to some degree. I do live in a humid area and thorough engine flushing definitly extended the life of my bearings.

FlyerGirl,

to answer your question and not argue about what fuel is better. I will say this. Pattern flyers tend to be very detailed in the way we treat our equipment. Much more so than an average sport flyer. We also tend to demand very high performance out of our equipment. The stuff will work so well that we can tell right away if something is off even just a little. Namely the engines for the most part are extremely reliable.

Now I'm in AZ also and we don't get the bearing rust problems that you may find say in Florida. Namely the humidity is not our problem. Fuel used will impact bearing life and also how the motor is run. Simply putting some after run in or simply using Cool Power will not always insure no problems. Saying that Cool Power is an outstanding fuel. I switched to it many years ago and my bearing problems as well as some other little issues went away. I then was fortunate enough to develop a relationship a few years later with Cool Power as a sponsored pilot. I just want to be up front when I endorse the product so people know. I stand behind the product 100000% I run the fuel at my choice.

Next item to consider. The pattern motors we use are very high output. We use larger than normal props on them and cooling can sometimes be more of a problem for us in a pattern model. The reason is most of the engines are now enclosed. So combine high output working hard, and sometimes poor cooling compared to your typical OS46 sport engine...the result is it is harder on the bearings. Consider this the engines are putting out say 5 times the power of the OS 46 almost 3.5hp in some cases and yet the size of the engine is only about 2.5times bigger. This motor is making more power on proportionally smaller parts. Look at a 4hp Lawn Mower engine. Its huge compared to a 1.4-1.6 pattern motor.

Another contributor is where you fly. Many parts of the country fly on grass. When you do the engine especially the 2 strokes with that use carb right down low and up front will ingest dirt, grass seeds and all kinds of crap. This is hard on bearings. The 4 strokes are little better in this department as the carb intake is behind the engine, but it still gets sucked up. We in AZ fly on pavement mostly because we don't have such a thing a grass naturally in the fields and local environment....this will extend bearing life also as we don't suck up the crap.

Now all being said Bearings will wear out. They get loose in the cage that they run inside from wear. Proper oil in the fuel will help this hence the Cool Power comments from above other posters. Not all fuels are created equal. There are many good fuels out there. But there are also some that are less desirable...remember really high output, high performance motors. When they get loose this can affect the way the engine transitions and outputs its power. So its common on pattern motors to change bearings about every 300 flights or so from wear. This is typically when the ring motor start to loose their performance. The performance change is very slow over time. Pattern guys use the power and need it. We notice when it falls off. So we go in and change the piston ring. These rings are again very small for the output of the engine and the result is they will wear out before say a DA150’s rings. Most pilots will just change the bearings when they have it all taken apart because it’s a cheap (around $20) preventive thing and besides the motor is already apart.

Now most sport flyers don't get 300 flights on their OS 46 in a year. But when practicing hard its easy to get 300 flights in 2-3 months on a pattern model. Now changing the bearings doesn’t have to happen on a schedule but in most cases pattern guys will change them to save the chance of it going out and causing damage to the motor. Sometimes a bearing failure can be from wear or from rust. In both cases the failure can mean metal flakes or even the balls flow through the engine. We have expensive motors and don’t want loose metal floating around in them. A tell tail sign of a bearing issue is glow plugs going bad. The small metal flakes or rusty ones will stick to the glow plug element and the plug will go bad.

So I know this is more info than you probably wanted to know…but it gives some why’s and what for’s rather than banter about what kind of after-run or what fuel to use.

Troy Newman
Laveen, AZ

Most serious "pattern" fliers put a lot of time on an engine, it is not uncommon for the top pilots to rebuild once a season. The serious local pattern guy (like me) can expect two or three seasons from a well maintained engine.

I have rebuilt dozens of engines, both two and four strokes. I find the average club flier does not know when his bearings are going bad. I have checked engines on the flightline on a typical summer evening and found several engines with bad bearings. The owners usually respond with "it runs ok". By the time bad bearings manifest themselves in a poor running engine, other damage can occur, like the big end of the conrod wearing excessively because the journal is flopping around. In the case of a riveted bearing, a rivet can let go and destroy the inside of the engine faster than you can say "what happened?" My test for checking bearings is to see if there is any play in the prop tips if you try and move them fore and aft when the engine is cold. If you can detect a wiggle, time to replace the bearings. The bearings in a four stroke tend to last a longer because they are not exposed to raw fuel as in a two stroke. As others on this thread have commented, the alcohol absorbs moisture and causes the bearings to corrode. After run oil used after every session will help protect the bearings. I find my YS pattern engines don't need after run oil until the end of the season, but I run them almost every other day throughout the flying season.

I also rarely change the front bearings unless the engine was involved in a crash, the front bearings seem to last forever.

Thanks that helps explain why pattern flyers mention rebuilds , new ring , etc. It sounded like the references to the parts changes were a matter of regular routine. I always assumed pattern planes had more than enough power so that gradual loss would not be big deal.

More than enough power never exists!!!!!! Sure there are some people that shouldn't be in control of such power, but to the discliplined pattern flyer, the throttle is a primary control, ideally full throttle should never be used in a normal sequence. Now I doubt that is ever going to occur, but you get my point. Get out there and practice, soon you will realise the importance of excess power on demand!!!
Cam