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R/C Tips and Tricks - Nitro Engine Break-In

Heat-Cycle Engine Break-In Method

I'm not sure of the original source for this (let me know if you do!), but here's a heat-cycle engine break-in method write-up (edited for clarity). I strongly recommend this over the idle method!

If you are still idling at least a tank through during break-in, you're using the old-school accepted method (still works well for some!) but it's not the method that the top engine guys recommend anymore.
The first several times you start your engine, heat it up with a hair dryer or heat gun first. That'll make it a lot easier to turn over whether you use a pullstart, roto-start, or starter box. As soon as it's running reliably, plop the car on the ground and begin running it around in a parking lot in 2-3 minute intervals and low throttle with the engine tuned only slightly rich, and get the temps up around 200F on a normal day. If the weather is cool and/or it won't warm up enough, wrap the head in a sock or in aluminum foil (careful with foil, if left loose it could cause glitching) to retain the heat. Don't lean the engine to get it to the proper temperature EVER! Not during break-in, not during winter bashing, never. Fuel going through the engine is what lubricates it, and if you go excessively lean, you'll risk permanent damage.
Every 2-3 minutes, shut the engine down, move the piston to bottom-dead-center, and let the engine cool to room temperature. Now fire it back up and continue this cycle until you've got about 15 minutes of run-time on it, then bump up to 3-4 minute intervals. Vary the RPM and again, get the temps in the 200F range. What you want is heat cycling of the components without the incredible stress that comes with breaking an engine in when it's overly rich and cold. After cycling the engine in this manner for about 20-25 total minutes, it'll be ready for performance tuning.
Yes, this method goes against the old-school "idle on the box" routine, but you'll be amazed once you've completed this break-in routine! Not only is it a lot more fun to do, but your engine will still have amazing pinch without sticking at the top AND your compression will last far longer than it will with the "old school" method.
If the piston and sleeve haven't expanded to operating temps, every time the engine turns over the piston slams into the pinch zone at TDC. The not-so-surprising result can be a cracked con-rod at the crank pin--that's where the majority of the stresses occur as the engine turns over. I've only heard of about 6-8 OS engines breaking con-rods, and they're ALWAYS during the first gallon...and almost every time it's because the guys have performed the "idle-on-the-box" break-in procedure. Doesn't seem like a mystery as to why it's happening. Drawing out this break-in routine over many tanks of fuel really stresses the engine & actually wears away compression along the way. This method I've outlined may feel weird at every step, but after you try it once, you'll notice a big difference in your engine's performance and life span and you'll never go back to the old method again.

Give this break-in method a shot, you'll be happy you did!

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