By Stanley Kwok

If there is anything that I learned from mechanics class, it would have to be only use nuts and bolts that were specifically designed for that particular application. This article is based on a true story. There was a guy who does his own modification on his car. One day, he installed a high performance clutch which was bigger and heavier than the stock part. The new clutch springs obviously had more pressure than the old ones. After the installation, he decided to check out his work and revved the engine up to pretty high RPM. All of a sudden came loud crashing sound and the clutch was literately exploded. Metal were shredding and pieces of the clutch were flying everywhere. The shrapnel pierced through the bell housing to the interior of the car. Fortunately the poor soul was revving the engine from outside and under the hood else his leg would look pretty ugly.

The Mingled parts were examined and the inspection revealed sheared bolts holding the pressure plate. The cause of this catastrophe was traced back to three things and they were: bigger and heavier clutch; higher spring pressure; and the use of improper bolts. The bigger clutch spinning at high RPM generated a lot of centrifugal force (throwing out force ) which put tremendous radial stress on the bolts. The stronger springs were constantly pulling on the bolt heads thus increasing the axial stress. The weakest link in this picture was the bolts which held the clutch to the flywheel did not have the tensile strength needed to cope with the extra stress. The combination of these forces were enough to shear the bolts right off. Had the guy calculated the extra stress into the equation and used higher tensile strength bolts the catastrophe could have been avoided.

The moral of the story is only use nuts and bolts of proper grade and strength in critical applications because the result can be disastrous as demonstrated by the incident.

If you have an article that you would like to share, please send it to V240G and I'll post it up.

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