I have been a fan of the miata for a long time. Lightweigh, rwd, convertible. So last year I purchased one in mint condition for my fiance. About 7 months after pruchasing the 90 miata it began having a severe loss of power, alot like the cluth slipping. When I pressed the gas the car was slow to accelereate, the problem began small but eventually got to where we could hardly get the car up to 70. I brought it to my mechanic to check out and he said the crankshaft key had sheared off and damaged the crankshaft and something else (i foget its been a while). He made a makeshift pin wedge thing to replace the original and told me this would only be a temporary solution. Just recently i've noticed the car, once again seeming as though the clutch were slipping. I hit the gas the revs hesitate momentarily and then climb while my speed doesent very much. Between this I talked to other owners who had said they had the same problem and were having to remove the engine or something or another to fix this. I searched this forum for the problem and unfortunately did not come up with much maybe I didnt search the correct terminology. What can I do to determine the problem? Can anyone provide any detailed information pertaining to the crankshaft problem? Is there anyway to seperate this problem from the clutch? To determine diffinately what my problem is. Any help would be appreciated. I've replaced the plugs and wires the first time, before I brought it to the mechanic, I did notice a little oil on one of the plugs but not alot.

Also some info that I saw that may pertain to the situation. The car habitually breaks what I assume is the A/C belt. Does that correlate with my problem?

 

Best check for a slipping clutch is to drive at a steady speed in say 3rd gear and depress clutch fully. Raise the RPM to around 4000 and then quickly let the clutch pedal back out. If clutch is good then RPM should snap quickly back down. If slipping then RPM will slowly drop back down.
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correct way to check a clutch is with a 2nd gear clutch test. hand brake on, 2nd gear engage, give it gas and release the clutch. If the vehicle stalls, you have a good clutch...