Hey guys,
I just got a new Thunder Tiger .46 pro abc bb engine. Right out of the box I noticed the shaft was stiff. I knew that it wasn't good to turn it over with out oil so I put some break-in oil down the throttle body and glow hole and tried to spin the engine. It spins but has one stiff spot as the piston gets around TDC. Is this stiffnes normal or is there a problem? I didn't see anything about this in the manual and I don't want to fire it up until I know its ok. Thanks in advance for any advice. -JDMiller

It's normal. Being an ABC-type engine there'll always be a pinch near the top of the cylinder. As the engine expands through heat the proper fit develops. Don't turn it through just for kicks until it's been broken in, or you just may break it. It's not unheard of for someone to damage the engine by doing that. There's a lot of pressure on the piston from the crank when you do that.

Agree with Mikel,turning the engine over by hand could damage that tight spot you asked about,also break in by the directions.

Also, the more you spin and ABC type (ringless)engine that is cold you place yourself at risk wearing out the "pinch" that actually provides you the necessary compression for it to run.

Once that "pinch" is gone, you will be looking for a new piston and cylinder liner or a new engine.

Yeh, what they said!

Exactly what they said!- Just make sure the instuctions mention the heat cycling break in method.- Its the right way!