Bad knock on engine people say flex plate on 1979 gmc 350 engine?

Answer 1

If it really IS the flex plate, that's a lot cheaper than other problems that could cause a bad knock.

The flex plate is a steel plate that bolts to the rear of the engine and has gear teeth around it. The starter engages with the teeth to start the engine. The torque converter also bolts to the flex plate. All power produced by the engine that is used to move the vehicle goes through the flex plate.

Flex plates get old and sometimes crack. When that happens you want to get the old flex plate out of there as soon as you can before it breaks completely and destroys the torque converter.

A flex plate is relatively cheap, compared to a complete engine rebuild or replacing the torque converter.

To replace the flex plate, simply pull the engine (or transmission, whichever is easiest), unbolt the flex plate from the crankshaft, bolt up a replacement and put the transmission (or engine) back.

Of course, there is more involved than that, but it's not as bad as some repairs.