Ball Bearing Engines

Stuka Stunt Main Forum · 10 of 10 known posts recovered

"Z" · Jan 11, 2001 11:10 AM

I am now the proud owner of a Double Star 60 BB, my first Ball Bearing engine. What is the recommended method of break in and just as important what should I use after my flying sessions to preserve the engines bearings. It is an AAC engine and I can't wait to get a plane built for it. Also any recommendations for props would be welcome too.

Thanks,
"Z"

LNeumann · Jan 11, 2001 03:18 PM

#1 source

On any ABC type engine (your AAC included) you should never run these in too slowly on the bench. You, essentially, want to run it in at the expected operating speed of the engine, although you may wish to use a slightly smaller (1 inch less diameter) prop at first. You, also, want to get it up to operating temperature as soon as possible, since these have a tighter "pinch" at the top and you want the cylinder to expand away from the piston as soon as possible. (This is the reason you don't want to run them too slow or too slobbery rich. They must get up to operating temperature quickly in order to break in properly.)

After that, it is just like "normal", and you may get a variety of answers. I normally run them about 5 minutes at a time, and then let them cool before running them again. While the engine is running you may need to adjust the needle valve to keep it at its operating speed, and it is good to pinch the line occasionally to allow it to go a full 2-cycle momentarily, just as it would when breaking in a maneuver.

Since this is a ball bearing engine, the shaft will not need break in time, so it will all depend on the amount of running needed by the piston. A little extra on the bench never hurts, so I would still give it 45 minutes to an hour before putting it in a plane.

The biggest problem with a ball bearing engine is the risk of getting rust in the bearings. Our fuels attract water, and the nitro in the fuel leaves a compound that can encourage rust (I am not a chemist. There are fancier words for this.) A good air tool oil makes a good after run oil. The stuff I like is Marvel Mystery Air Tool Oil (Not car oil. That is different.) The air tool oil has a rust inhibitor in it, and does not evaporate and gum up like 3-in-one (bad stuff) does. Also, unlike most car oils, this stuff is compatible with our fuels and doesn't make the first start of the day difficult as with some other oils. You can actually start the engine on it. So use it liberally, if you want. It is best to drop a bit of after run oil in the engine after every session, and definitely when there will be a longer time between flying sessions (like a week or a winter.)

As to props, I think Tom Dixon recommends a 12 x 6 BY&O prop for these engines, although I would think they should be able to take a 13 quite easily. Generally a 5 to 5.5 inch pitch should get you in the "ball park" (The 12 x 6 BY&O measures out to about 5.5). The best thing to do is to experiment, as some will depend on your plane and fuel and line choices, and a lot will depend on you and what you like.

Leonard Neumann

Bill Hummel · Jan 11, 2001 08:52 PM

#2 source

We've had several Double Stars in the club...including the 60BB.
All benefited from adding head shims; 30 or 40 thousandths was not unusual! Better runs, less sensitive to needle adjustment. We also found too much oil hurt the motor run...20% oil, with 5% nitro seemed about the best in most weather. Finally, the B-Y&O 13-5 prop was outstanding in the 60 engine. Best plug was the Glo Devil 300 R/C long.

LNeumann · Jan 11, 2001 09:27 PM

#3 source

Some of the engine reworkers with the ST 60 will hog out the head which is similar to what you are doing in adding head shims. I have seen hemi heads with the entire squish band removed. I am curious. When you say 30-40 thousandths...is this the total amount, or you adding that amount in addition to what comes with the engine?

Leonard Neumann

Randy · Jan 11, 2001 11:15 PM

#4 source

>>A little extra on the bench never hurts, so I would still give it 45 minutes to an hour before putting it in a plane<<

Note that this will really vary. Took almost 3 hours of bench time to get my Stalker 61RE to break in (really hard piston and cylinder). About 2 hours for a PA.61 and about an hour for a PA.40 I have. The one way to tell is that you no longer have to mess with the needle to maintain RPM. You start the engine and it will run dead steady (or nearly so), without you touching it, for the entire tank. Also, if you have a test stand like mine, you can run the engine, tilt it up and it will readily break into a 2 cycle, lower it and it will immediately drop back to a 4 cycle.

My buddy Pat runs ST .60s and the Double Star 60BB. He uses a BY&O 13x5 and (his favorite prop) a RevUp 13x5 and 13x5EW. Course, He uses 14x5s too, but the guy likes kayak paddles on the front of his planes. The engines sure run nice.

Randy

Brad Walker · Jan 12, 2001 09:58 AM

#6 source

>My buddy Pat runs ST .60s
>and the Double Star 60BB.
>He uses a BY&O 13x5
>and (his favorite prop) a
>RevUp 13x5 and 13x5EW. Course,
>He uses 14x5s too, but
>the guy likes kayak paddles
>on the front of his
>planes. The engines sure run
>nice.

I also use the BY&O's on my Greenaway 60 with excellent results. I have found that the 13-6’s range from 4 to 6 pitch and the 13-5’s are 3.5- to 5. My current good prop is 13-4.25(which correlate to your 13-5), and I think a little less pitch would be better. Do you know the actually pitches of your props? Have you found that the BY&O’s require less pitch than the Rev-UP’s?

LNeumann · Jan 12, 2001 11:23 AM

#7 source

I am assuming that when you give the ranges here, you are talking from the hub on out through the rest of the blade. There will always be some variation from blade to blade and prop to prop, but these should all be quite consistent with one another unless the person making them goofed or the blades, themselves, warped (which can happen with wooden props). Rev-Up props are notorious for being under pitched--and also have less pitch at the tips. Thus the BY&O should have a little more than the Rev-UP when comparing numbers with one another.

Leonard Neumann

Randy · Jan 12, 2001 11:41 AM

#8 source

LAST EDITED ON Jan-12-01 AT 11:43 AM (EST)

Pat re-ptiches, thins and generally cleans up the blades of the BY&O and usually re-pitches the RevUps. A 13x5 is a 13x5 for him. He's been using (at least last summer) a RevUp 14x5 cut down to 13.5x5 that is cleaned up and re-pitched. Pat seemed to like that one a lot.

This is the guy that was feeding me props for a Stalker 61RE I was using a couple of years ago. We ended up with a RevUp 14x6 that had been cut down to a 13.3 and re-pitched to 5 at mid blade and 5.5 at the tip. Man, that prop worked great on that engine.

Randy

Bill Hummel · Jan 12, 2001 09:12 AM

#5 source

Leonard,
We actually add 2 to 5 of the ten thousandths shims to the Double Stars. Flying buddy Rob Aronstein added 5 shims to his 40, now has one of the best running traditional motor runs I've heard. We have added 2 or 3 shims to the 60's, with similar positive results. We're guessing that the engines are set up for low or no-nitro fuels, and the shims knock the head pressures down a bit. Easy to try!

"Z" · Jan 12, 2001 05:45 PM

#9 source

Thanks for the info. I really appreciate the responses and you have more than answered my questions

"Z"