The crankshaft that came from the “boat anchor” block I purchased was severely pitted around the rear main seal.  This was a bummer, as I really wanted to use one of the newer crankshafts with the larger thrust bearings.  The larger thrust bearing sizes did not start until the 1999 model year.  Unfortunately, all of the used cranks I have access to are from 94-97 Miatas.

I could not locate a used 99-05 crank so I called Mazda Comp.  Turns out the price of a new crank is $580, so that option is out.

In the mean time, Mike learned that sleeving the crankshaft would be more difficult than other engines are.  Usually, a 0.010” sleeve is pressed over the crank.  Mike thought this would work well because the Miata’s rear main seal is quite soft and appeared to be able to flex around the additional width of the crank.  Not all seals are flexible enough for this solution to work.  Luckily, before parts were ordered and work started, it was determined that there is a ridge on the flywheel that needs to fit over this part of the crank.  The sleeve wouldn’t allow that.  If we were to go forward with the sleeve repair, the crank would have to be machined and then a repair sleeve which would return that part of the crank to the original circumference would have to be used.  This seemed overly complex and involved a few too many “ifs” for my liking.

As fate would have it, Mike found a remanufactured crank for a good price.  The crank should be delivered early next week.  Since the crankshaft journals were going to be ground anyway, the cost of the remanufactured crank is not that much more than the outsourced labor for grounding the crank shaft would have been.  That’s a win, but Mike and I will feel better when he has the crank in-hand and can evaluate it for himself.

Why all of this bother on the crank?  After comparing the earlier 1.8 cranks with the 99+ cranks, the difference in the thrust bearing size is obvious.  All of this talk about crankshafts and thrust bearings has inspired me to remove the starter/clutch override switch.  There is nothing like actually looking at the cranks to realize just how much force is being placed upon a relatively small area on the crank at startup, and with zero oil pressure to boot.

PICTURES: Crankshafts and comparison of small vs big thrust bearing location