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Best way to heat cycle 2 stroke

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Just rebuilt my sons kx 85 complete bottom end and top. Was wondering what was the best way to heat cycle before racing it again.

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Bring it up to temp by blipping the throttle, not real high rpm, let it cool COMPLETELY. Repeat a couple times. Rip it!

We've done that so far 2 times for about 10 mins. each time got fairly warm. Should be good you think?

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The best way is to not waste your time heat cycling it in the first place.

Exactly. Start and warm up the bike, monitoring the engine for any leaks and abnormal sounds. Once the radiators are warm to the touch, ride it.

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If you heat cycle your bike 3 times 10 minutes each you are losing your chance at good ring seal.  The crosshatch in the bore will more or less file the rings to fit the bore and excessive idling will take the edge off the crosshatch while at the same time not seating the rings.  You need cylinder pressure to seat the rings that means warm it up and run it! 

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Warm it up and ride it moderate to hard.  Don't idle it forever in the garage, and don't pin it down the street.

 

Cleanest pistons I've ever seen were after making sure it runs and racing the next day. Only because I just can't resist the urge to fire it up in the garage.

 

This is especially true for minis.

Edited by ubu
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If you heat cycle your bike 3 times 10 minutes each you are losing your chance at good ring seal.  The crosshatch in the bore will more or less file the rings to fit the bore and excessive idling will take the edge off the crosshatch while at the same time not seating the rings.  You need cylinder pressure to seat the rings that means warm it up and run it! 

Lots of speculation there. Blipping the throttle puts the same pressure on the rings regardless of how the engine is being used. The engine has no idea if it is in the shop or on the trail. Even Honda engines are not that smart.  ;)  Really. But you are correct, no engine should ever be at idle for long periods of time. Air or water cooled. Ten minutes is too long.   My CR's cylinders are usually plenty warm after three or four minutes of blipping. Moderate blipping. Now,,,whats the best oil?

Edited by YHGEORGE
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Lots of speculation there. Blipping the throttle puts the same pressure on the rings regardless of how the engine is being used. The engine has no idea if it is in the shop or on the trail. Even Honda engines are not that smart.  ;)  Really. But you are correct, no engine should ever be at idle for long periods of time. Air or water cooled. Ten minutes is too long.   My CR's cylinders are usually plenty warm after three or four minutes of blipping. Moderate blipping. Now,,,whats the best oil?

But there is a difference between blipping the throttle vs accelerating when riding.  Much higher cylinder pressures are created when riding and the engine is under load, which seats the rings rather quickly.  Without a load on the engine it's just spinning free with much lower cylinder pressure, honest.  :)

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But there is a difference between blipping the throttle vs accelerating when riding.  Much higher cylinder pressures are created when riding and the engine is under load, which seats the rings rather quickly.  Without a load on the engine it's just spinning free with much lower cylinder pressure, honest.  :)

Agree, I was about to argue that the engine does know the difference between being in the garage and out on the trail.

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The clutch, gearbox etc does but the rings don't.

Your engine can very much tell the difference between being loaded and unloaded. 

 

No load means there is no output torque, meaning the throttle controls the RPM. Cylinder pressure is low.

 

Full load means there is maximum output torque at a chosen RPM. This always happens at full throttle. Cylinder pressure is high. If there is no resistance on the crank at full throttle, the motor will over rev. 

Edited by ubu
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I dont agree with George that the loads are the same.

 

I DO agree with YHGEORGE that people over think this and his initial advice is correct.

Edited by BushPig
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Start it, check for leaks, ride it like you usually do. The rings require cylinder pressure to seat and this needs to happen pretty quickly after initial startup.

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Everybody has an opinion on this.  I prefer a run on the stand will checking for leaks, etc. until the engine is warm.  Complete cool down.  Then an easy ride for 10-15 minutes around the yard/neighborhood.  Cool down.  Ride/race  as normal.

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