brashy

hi ive fitted a flywheel thats been lightened by a friend but im unsure hes balanced it would this course my engine to run sloppy an my the car vibrate slightly

Splitpin

Okay, a few things don't add up here.

Is your friend an engineer, or...? If your friend knows what he's doing and has access to proper facilities and tools, he will have balanced it.

If your friend doesn't have access to the correct kit, he probably hasn't balanced it, and if that's the case you don't to put a twenty pound piece of steel that's been attacked by a numpty anywhere near your car, let alone spin it 7000 times a minute.

An out of balance flywheel (only by a few grams) will make your car vibrate. If it's really bad **** nose what it could do. It's also eminently possible that the "sloppy" running is a fault picked up somewhere in the gearbox removal and reassembly.

We can't really advise without knowing your mate.