I know that break in instructions will come with my engine, but I haven't bought it yet so I'll ask this anyway. TT Pro .46 / .61, should you fluctuate the speed while breaking in or let it run at a constant speed?

This topic has been hashed over, and over again, but here goes:

Follow the instructions. If they are lost, lots of 5 min runs, with 10-20min cool down in between. 1st run, 3 turns out, full throttle for 1 min with glow plug attached. Slowly tune for that point where it goes between 4 stroking and two stroking. Next runs, lean it a click or 2, pinch the fuel line for a split second, it should jump in rpm, if it dosen't it's too lean, back it off. Pinch it every 30 sec, just for a split sec. Eventually it'll make less and less of a difference. More 5min runs like the last, all at full throttle. You should see plenty of smoke out of the muffler, NEVER lean it all the way for max rpm. When you have 30 or 40 min total run time, try to set the idle. If it will not idle, a few more 5 min runs should help.

Fuel should be low nitro with 20 plus percent oil. Lots of castor in the mix. Never run it slobbering rich. The metal will not come up to operating temp this way, the sleeve will not expand all the way, the sleeve will wear in at the cooler temp, and when you do exentually run at a leaned out 2 stroke hot setting, it'll never produce the power it was capable of. GMS are very good, powerful engines, and require longer than usual break-in.

After it's had 30 or 40 mins worth of 5 min runs, I usually go fly, (rich). Do lots of loops (not all in a row of course), at different throttle settings. This way it leans a bit, then richens up. Lean it up just a bit between flights. It'll really last a long time if you keep it off peak. I point the nose straight up, and tune so a quick pinch will audibly bump the rpm.


Here's some more threads:
http://www.rcuniverse.com/showthread...kin#post348166
http://www.jettengineering.com/faq.html#faq8
http://www.rcuniverse.com/showthread...kin#post431044
http://www.rcuniverse.com/showthread...ch+and+breakin]

Thanks for the info and the links. There is certainly more to breaking an engine in than what I had figured.

Take note of rsieminski's comment: "Never run it slobbering rich. The metal will not come up to operating temp this way, the sleeve will not expand all the way, the sleeve will wear in at the cooler temp, and when you do externally run at a leaned out 2 stroke hot setting, it'll never produce the power it was capable of"

I have a 46fx that is between 500 and 1000 rpm short of where I am pretty certain it should be. The best explanation I've come up with so far is the break it. I think the engines first couple of runs were way too rich. I recall trying to be very careful not to let it get too hot, thinking that that would be harmful.

rsieminski - that is the most succinct, zero hand waving, statement I've read yet about engine break in and what it really accomplishes. Now, I think I too get it.

Of course this is for 2 stroke non-ringed engines
Rsieminski: you should be on Reader's Digest most wanted list with that succinct and excellent breaking in method )
REgards,
Patrick

succinct it was, :bananahea

Nov. 2001 MAN had a good article on breaking in engines. For ABC type engines: Use highest nitro content recomm. by engine manufacturer, and at least 20% oil with some castor. Use a prop that is one size smaller than the recomm. flight size. Start engine and adj needle for rich 2-cycle operation . Run 1 min. at full throttle, and then let the engine cool down completely . Repeat this step 4 - 6 times. Run 3 min. at full throttle, and let cool down. Repeat this step 6 - 8 times. Engine should be broken in at this point. To check, start engine and let warm up. Lean to peak RPM, and then richen 200 - 300 RPM (use a tach). Listen to the engine and watch the tach. The engine should hold this semi-peak RPM for at least 30 seconds. If it starts to slow down, richen the mixture immediately and repeat the 3 min. runs. I had a terrible running MDS 48 that I thought was broken in. I broke it in again using the above method and it now runs great. Apparently, its the number of runs (thermal cycles) that does the trick, not the amount of fuel run through the engine.