motoxskp

I was wondering how to tell when engine needs rebuilt. The reason i ask is because mine has lost all power and is very hard to start. (although its not that old). its a vx.18 by the way. I took the piston and sleeve out to look for any defects but cant find anything. Once i do get it running there is no power and it sounds realy muffeled. (it also doesnt want to idle)

overrev

If the motor turn over real easy then you are losing compression and need to replace the piston and sleeve. The loss of compression will cause you to lose power like you described.

Chris_RC

What break in method di you do? How much fuel through the engine? Did you store at Bottom Dead Center after running? And what temps did the engine run at? Are you a good tuner?

motoxskp

Yes and No Chris_rc. i broke the engine in correct but i was on a learning curve as i tunned it.(this is my first rc). so i learned alot while doing the tunning but may have ran it alot leaner at times then i should have. It has about a gallon thru it and has no power now, and i have no clue on what temps i was running at. but just so you know i have learned from my mistakes and bought a temp gun for my other (savage ) rc. so i dont ruin it.

ShoestringRacer

Loss of power and trouble idling are classic symptoms of a worn piston/sleeve which means the pinch - which is what seals the combustion chamber - has decreased to the point to compromise proper running. When the pinch is gone there is combustion gas blowby into the crankcase which leads to a loss of power and generally creates all kinds of havoc including poor throttle transition, trouble idling and power loss. When the pinch/compression is gone or decreased where you can notice at room temperatures the problem manifests itself when the engine warms up because the brass sleeve expands more with heat and makes the tight piston/sleeve fit excessive causing combustion blowby.

By looking at them it is likely you wont notice any physical signs of a worn piston/sleeve unless of course the engine has ingested some dirt/debris which has scored the piston. Many engines last for several gallons of fuel but don't be alarmed if a particular engine lasts much less; especially if it has been run overly lean and/or otherwise abused.

You may want to see my post in this other thread which has some engine information:

http://www.rcuniverse.com/forum/m_87...tm.htm#8764466

Spetz

Are you sure it's tuned right and doesn't have an air leak?