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Break-In Bench?

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R

RobH

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I found this pic in the gallery. I was curious if anyone can tell me the sequence of parts required to mount a propellor into the shaft of a .21 engine. I know exactly poop about rc airplanes.

Thanks,
Rob
 
I would say just a spacer where the flywheel goes and a clutch nut. You wont need perfect balance if you use a lightweight PLASTIC prop. I would stay away from a heavy wooden one as that would want to be balance or could cause excessive abuse on the shaft/bearrings. Most any LHS that deal in airplanes will have a LARGE selection of props. Take your mill in with you and size them up. Even if the prop center hole is too small you can drill it out a bit. Just make sure that center hole isnt too big so it doesn't slosh around.

I know a couple guys who break-in their mills on benches and they swear by it. I still have yet to do one that way but I would assume its less frustrating and you can do it in the comfort of your garage. Just make sure you have good airflow in the room.
 
That's a sweet setup. I'll have to dig around my airplane part pile and see if I can rig something like that up. Starting a non-pullstart engine will be a challenge though. I hope you can flip start it like an airplane.
The balancing of props is about the same for plastic or wood. I had to sand down both to get them balanced. I don't think it will be much of an issue with that small of a prop (7X4). Personally I prefer wooden props. If something happens to get in the way of the prop, the wood will break. Plastic prop will slice you up like a Ginsu knife. :)

Tex
 
Dont see why you couldnt bump start it if you put the flywheel on it. Just rig a Starter Box wheel to the end of a drill...no??
 
Even if you could rig it up with a flywheel, that's getting mighty close to a spinning prop. One slip and you are in for some of that Ginsu action I was talking about. You pretty much have to start this contaption from the front.

Now here is a bench you can buy from Serpent. But at 200 bucks? I think I will try to rig one up myself. :)

Tex
 
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That's crazy... Looks as though he's not using a header and going straight to the exhaust.. I like the electrical tape around the heatsink. That should leave some nice stickiness to it.
 
That is an interesting set up. If you are going to use a bench to break in your engine and plan on using the propeller...then get the right stuff to do it. They make propeller nuts or flywheels for engines to hold a propeller. You can get a spinner to put on it and then use a bumpstarter made for bumpstarting aircraft engines.

I concur with the advice on taking the mill to your LHS to size and obtain the right aircraft hardware to place on the engine. As for propeller type...I'd go for a decent sized wooden one. Most RC props are balance fairly well (they kind of have to be for flying), and you want to place a reasonable load on the engine. Why? so that you do not over rpm the engine during break in. Too much rpm too quickly...and the thing may get broke before you get it off the bench.
 
That photo is from my gallery. The engine is mounted to an old cybermaxx chassis clamped upside-down, with about an inch cut off the end. The prop is an APC 7" dia x 4" pitch. Mounting it was tough. I had to make a spacer from aluminum on a lathe to keep the prop from hitting the carb, but that left almost no threads for the nut. I cut down the hub of the prop on the mill until there was enough threads. If there is any interest, I could make adapter fittings to thread onto the shaft and hold the prop safely out in front.

I got this technique from the Ultimate Nitro Tuning Guide, which describes the process in detail, and shows a picture of the same bench from Texsavage's link.

Making this was a bit of work, but it only cost me $4 for the prop. I have used it twice now and the technique really works.

But you dont need to go to this much work for proper breakin. Most of the secret is simply to get the engine hot before starting the first few times, and keep it above 200F when it is running. This is to ensure that the cylinder expands enough and doesn't wear too much off the piston on the first couple starts.
 
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