Im considering doing a engine swap in my crf 70 pit bike what your opinion??

http://cgi.ebay.com/ebaymotors/150CC-ENG...

It's a Yinxiang - one of the 200+ companies in China making motorcycle engines right now.

Quality control and metallurgy are the issues with these engines. We've seen some good parts, and lots of bad parts from these off-brand companies.

In new engines from the factory we've seen rust, pieces of metal and aluminum in the engine, improperly fitted pistons, valves, etc.

There are no replacement parts available from the original manufacturer. Most aftermarket parts made for other minis will fit, but you will start to have reliablity issues if you modify the engine much at all.

This engine appears to be a combo of 2 popular engines, the bottom end is the Xr/crf 50-70 type while the topend is based on the kawasaki klx110. It appears to be well made from the outside atleast and the klx style topend is a much more modern and efficient design than the old honda one.
I would ask who exactly makes this engine and the availability of spare parts. The best replacement engines are made by the Lifan company. If this is a lifan I would feel confident of its power output and reliability. But I have no expirence with this one.

I think that engine is a Chinese and worth about half what they are asking for it if that Did you read the Mfg's name?

Personally I wouldn't put that Chinese made turd in my bike. I would spend that money on Powroll performance upgrades on the existing engine.

http://powroll.com/P_HONDA_XR70.htm