Some questions about a first build.

[karl]

Many flywheels are hammered off, or pryed off, or subjected to some grease monkey abuse. So you never know on a used engine what you might be dealing with, but " brand new" I think a flywheel is a pretty stable component beyond 6k.

I feel safe spinning the cast flywheels 4-5k, but over 6k is asking for trouble.

They can explode with hand grenade velocity once they get up near 6K rpm., on that "DragginBallz" minibike it could've taken a foot off right through the ankle.

That's if your lucky, only loosing a foot.

It's not worth risking your life over a $100 flywheel. Yes I have spun a stock flywheel to 7k without incident,
but Ive also had one loose the flywheel magnet, that was a good bang.

One poor casting is all it takes, and we are talking chinese engines built down to a price here.

But like I said, I'm a bit skeptical about the longevity with these small 4 cycles turning out crazy RPM.

The cylinder bores wear out quick once the rpm's and compression ratio are cranked up.

Ive worn out two predator blocks already, 50 hours ya did good. Changed oil every couple hours runtime,
one engine mobil-1 with zinc additive, other shell rotella diesel oil. Both bores look the same.

 

[madprofessor]

I might remove the governor and get a tachometer and run a maximum peak of 4500.

Good plan, but Superman or The Flash you ain't. You hammer down on the gas to reach your stated rpm, then throw the chain, you ain't gonna realize it then be able to get off the floorboard fast enough to keep from zingin' it to way past safety.

 

[Millwright]

A good possibility of over rev for sure!
Do you know if or how to change the governor upper limit?

 

[madprofessor]

We just had a long back and forth about that for Predators on another thread. The eventual answer was loosening the bolt for the pinch point that holds the governor arm to the governor shaft sticking up out of the motor, and twisting it in the correct direction to increase or decrease the setting, flooring the accelerator, then retighten bolt. A trial and error thing, could take you from 1 to 1000 tries to get what you want. Need to grab the shaft while loose first and twist it to its stop in ??? clockwise ??? direction before adjusting arm position, can't remember direction for sure, will try to find it for you. Info to work out answer came from Youtube videos.