Due to excessively abusive service, small radial heat cracks sometimes occur in the driving face of the clutch pressure plate. These cracks are usually local in character and extend only a few thousandths of an inch deep. See Fig. 801.

Heat cracks are caused by exceedingly high frictional temperatures and their resultant rapid dissipation. These cracks do no harm and in no way interfere with the correct operation of the clutch.

It is recommended that pressure plates found in this condition be carefully cleaned with naphtha and then polished with a fine grade of sand paper. Extreme care should be exercised to remove all abrasive material .with clean cloth after this operation is completed. The clutch cover plate assembly should be replaced with a .new one, only when its driving face is scored. This is usually caused by the presence of foreign abrasive matter between the clutch driving faces and the friction facings.