RX-7 engine vibration (sometimes)
 

1987 RX-7 120,000 miles We have developed an intermittant engine vibration that is most noticeable in neutral with the clutch out, though it is present sometimes while in gear. It was noticed after a skilled Mazda repair shop's clutch replacement, but we believe it could not have been caused by the clutch work. It was first thought to be indicative of a worn universal joint, but clearly is not, because the vibration is present when the car is standing still.

The vibration becomes more noticeable as one increases the RPM, but is completely absent when the clutch is depressed. The mechanic who did the clutch work suspected that it has to do with relaxing the pressure on the throwout bearing, allowing the crank(main?)shaft to shift aft of the position in occupies with the throwout bearing depressed.

We originally thought that the vibration was caused by an out-of-center positioning of the pressure or clutch plate, but since it is intermittant, these explanations seem unlikely. But we can't come up with any other hypothesis. I've never disassembled a rotary engine, so have no clue as to what might cause such an intermittant vibration. Once present, the vibration is present until clutch is depressed. It sometimes does, but sometimes does not reappear the next time the clutch is released. It is present about 50% of clutch-release occasions. Transmission is quiet and there is no leak that might indicate a sloppy front-end transmission bearing that would cause the pressure plate to lie out-of-center sometimes.

Any ideas? Anybody else ever experienced this phenomena. Please feel free to send e-mails directly to rhbohl@aol.com or call 415-751-3447.

Roger Bohl

RE: RX-7 engine vibration (sometimes)
 

How does the rear tranmission mount look. Not necessarily the two on each side of the mount that control lateral movement but the one in the center. They are very commonly torn apart and can then transmit powertrain vibration to the body right under your seat.