miata cars repair

Miata Engine Build Part 1 - Sourcing A Long-Nose Crankshaft

by Dan Hankewycz
Read Time: 3 mins

The turbo miata is a 1990, which means it has a short nose crankshaft that suffers from pulley wobble. I’m slowly collecting parts to rebuild the motor, and one of the parts I’ve needed is a long-nose crankshaft from a 91.5-93 miata. I recently saw a 91.5 miata show up in my local pull-n-pay junkyard, so I quickly went over and snagged it. Here’s some photos of the process.

Pulling The Crank

It wasn't easy being by myself. Luckily someone already took the trans. I pulled the head and accessories and was able to drop the bare block and oil pan out of the bottom of the engine bay.

Empty engine bay. Pulled the oil pan off. Found some milky looking oil :/ Getting the main caps off was pretty easy. The rod caps were a pain though; they needed some convincing with a hammer... You can see significant grooving on the main bearings. I think this might actually be from rust forming on the crank while the motor was sitting. More on that in later photos. It was raining on and off the whole time, so it didn't make things easier. I kept taking shelter in another car.

Taking It Home

I forgot to bring a 21mm socket for the front pulley, so I had to wait until I got home.

Front keyway looks to be in good condition.

The main surfaces aren't in the greatest condition, but I'm hoping the machine shop can clean them up. This surface rust (or whatever it is) concerns me the most. I thinks it's from the motor sitting out in the elements, but it's hard to tell.

Conclusion

The crank cost me $30 and it only took me 2hrs to pull it out of the car. I’m hoping it’s not too far gone and that a machine shop will be able to clean it up. Looks like you can get a set of ACL bearings in 0.025, 0.25, and 0.5mm over standard. Hopefully it doesn’t take 0.5mm to get this crank back into shape, but we’ll see.

Next: Part 2 - Change Of Plans…

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