A few corrections.
The 1990-93 viscous LSD was a standalone option, the 1994-05 Torsen was always tied to various packages. It wasn't a standalone option. If I remember correctly, if the car has a power radio antenna it has a Torsen. The big exception is automatics, no automatics came with the Torsen. A call to Mazda customer relations (800-222-5500) can clarify for a particular car, but any leather car with a stick will have a Torsen. I know for a fact that the GRM buyer's guide doesn't say the Torsen comes as a standalone, and if you want a more fully researched option package list check Mazda Miata: Find It, Fix It, Trick It.
The 1991-93 1.6 crank nose is the same as the 1994-05 cars. No Miata will be happy if you don't torque the crank bolt properly. The appropriate repair for a damaged crank depends on how bad the damage is. Check out "Loctite repair" for the full recipe put together by some Australian engineers who work at Loctite. On an 83k 1990, I'd find out if the belt has been changed - and if not, use that as an opportunity to inspect the nose yourself. There are far more healthy Miata crank noses out there than bad ones. The failure rate on the similar GTX crank seems to be dramatically higher for some reason. Personally, I'd only replace the hardware if I saw signs of wear, and usually the wear is due to a loose crank bolt. The one thing you do need to do is torque the bolt correctly and use blue Loctite on it.
This one in particular I have to address directly.
Javelin said:
Next, the NB shock conversion is stupid easy. Use the NB mounts on the rear shocks. Done. FM's fancy ones are basically NB mounts.
This is not true. If you simply slap NB mounts in place of NA ones and bodge around with some bushings to make it fit on the NA shocks, you'll find the car will drop about 1/2". If you only do this on the back, the back of the car will drop. The FM mounts are a custom-made piece with different geometry that will keep the same ride height as the NA mounts but add considerably more compression travel. Very different than a factory NB part.
The smart way to do an NB change is to swap out everything together: springs, shocks and upper mounts and associated bushings. FM does sell their shock packages like this, and it's a straight bolt-in that will still ride at the design ride height of the springs.
At 130k, a Miata is either due for a timing belt change or it had one in the past 10k. There are are a lot of very conscientious Miata owners out there who do follow Mazda's recommended maintenance schedule, so don't assume it hasn't been done. But the good thing is that, if the change was done, it was probably done by the current seller so you can find out. I consider the lifespan of a Miata belt to be right around 80k - some last longer, but I've pulled a couple of broken ones out of cars with this mileage.
Square left in 50 caution ocean!
