Hot spot/ Burnt flywheel ? Clutch break in?

Hi,

What causes hot spots or a burnt flywheel? Could it be due to improper clutch break-in? What would be a proper clutch break-in method ?

Overheating is most commonly from excess slip.

This can be caused by very aggressive driving such as hard launches, power shifting, but I've also seen it caused by resting one's foot on the clutch pedal while cruising, or trying to be so smooth that the clutch gets dragged for a while. I've also seen it caused because clearances were improper so full engagement didn't actually apply proper clamping force.

Do you have any more info on the situation?

Actually i was thinking about one of the built i did for a customer few years ago where i wasnt sure why that happened. The car definitely had hard launches from drag racing. Is that normal though?

Any time a clutch is slipping, heat is being generated and it will usually transfer into the pressure plate and flywheel. If there is a point on either of these components that has a flaw or high spot, this will concentrate the heat build up, which then leads to the metal going through a phase transformation if it gets hot enough. When this happens the material is hardened in that small area, so it is therefore tougher than the surrounding area, the problem compounds itself until the components are resurfaced (usually only a temporary solution, as not enough material is removed to get back to the base material) or replaced.

Stephen nailed it. There may be slight variations in the carbon distribution in the iron/steel, which may affect the wear and then as the clutch slips/is slipped, it happens as described.

If there IS a hard spot and/or discolouration, inspect the flywheel carefully for heat crack - they WILL weaken it and in extreme cases cause the flywheel to shatter/explode. This is a SERIOUS concern, as a high rpm failure can destroy EVERYTHING around it - not just the bellhousing*, but engine blocks, gearboxes, firewalls, floors and part of the body in the vicinity...

*That's why most race organisations require "burst proof" bellhousings/enclosures.

So i guess there is no way to avoid this right]? i mean in the context of drag racing, where the driver will feather the clutch as to get preload and causing slipping action. Unless he/she does the clutch drop which might have negative effects on other component such as the driveshaft.