How to install a bigger crankshaft

[gitsum]

Originally Posted by blueboy5000

A gy6 150cc should easily do 50mph at 6500rpm. Riding at WOT is extreme;y bad for ANY engine, not just scooters, NOTHING is designed to run at WOT.

It's not WOT that is bad for any engine. It is the combination of high rpm's and excess heat that will significantly reduce the life of an engine.

That being said, WOT on most GY6 engines usually runs the rpm's at or near redline and the air cooled engine starts running pretty hot. I have a Taiwanese GY6 scooter that's tuned to run around 6800 rpm's at 55-60 mph and the engine temps usually run 320-340 degrees (CHT gauge). My philosophy is under 350 f and sustained rpm's under 7000 rpm's, no need to worry about speed or actual throttle position.

The wife and I have been touring two up riding like this for up to 300 miles a day. Close to 5000 miles and counting. I expect to get at least 25k out of the engine. When running the scooter hard like this I make sure to change the oil every 500 miles and check the valve lash every 1500 miles (only one adjustment needed so far).

I had a Yamaha C3 that was fuel injected and water-cooled, it ran WOT for nearly it's entire life. Last I heard it's still running strong.