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06-12-2010 | 03:07 PM

#268

DarZeelon

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From: Rosh-HaAyin, ISRAEL

RE: Tapered-Bore Engine Break-in - Upgraded

Quote:

ORIGINAL: le fou

I need some serious help! I followed the procedure indicated at the beginning of this thread and I was still able to ruin my piston & sleeve... I know that because my pinch at TDC without the plug is quite reduced.

Le Fou,

It is not necessarily ruined...

Some engines are 'looser' than others and some are really loose.

Quote:

So, I have a Magnum .91XLS and I added 60ml of castor oil to 1 liter of 15% nitro with 18% blend oil as a baseline. I think that the fuel is OK I mounted the engine on a test bench. It seems that during some instances the engine overheated during the break in without any changes on the high speed needle valve, at what point I stopped the engine or made it more rich. Before the first run, I used my heat gun to pre-heat the engine. I started with 1 minute run and let the engine cool off completely before repeating this cycle 5 times. Then I ran 3 times the engine for 5 minutes leaning it somewhat while monitoring the temperature. I allowed the engine to completely cool off between the 5 minutes runs.

While breaking an engine in, one must not be oblivious to it overheating...
The mixture must be set ~500 RPM richer than peak. This should be monitored by an occasional quick pinch of the fuel-line.
If it causes the engine to speed-up, the setting is OK... If it sags, it is obviously too lean!

Quote:

I ordered a new sleeve and piston and I would like to know if you could give me the following recommendations. Basically, I am looking for a procedure that will make the break in fool proof and protect the engine from the user

1) What propeller size to use for break in? Manual states 14X6 but in other posts, I have been told to use 12X7 or even 11X7. I plan to use my engine on a patriot XL.
2) How many turns should I open the high speed needle valve? Manual indicates 2 1/2 turns.
3) What RPM should I shoot for when I first start the engine?
4) What temperature should I have for target? 350 to 380 degrees Far ?
5) How long should I run the engine at first? 1 min or 30 seconds. The Magnum break in instructions recommend starting the engine at half throttle for the first minutes but I don't think it is what should be done.

Nothing is fool-proof, because...

First, make sure you are not wasting your hard-earned cash on replacing good parts... Are the current sleeve and piston scored?
If not, the pinch does not have to be like new, just perceptible is enough for most engines.

1. For a .91 two-stroke engine, I would say a good break-in prop is a 12x8.
2. As many turns as it will take to have the engine running 500 RPM richer than peak - I don't know how much it is in your engine.
3. You should target an RPM level "500 RPM richer than peak" - peaking a new engine for a moment does no harm, so you can check.
4. You should target whatever temperature it is running at, "500 RPM richer than peak". I don't know what the exact °F value is, because this is not what I am looking for.
5. The first two-three runs I do are short, 20-30 seconds..., just to make sure no heat-soak takes place. Then full 5 minute tanks.

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