Crank(y) Shaft Pulley Part III

Well the weather has turned and the sun is out so the Mazda should be coming out of its winter hibernation, but alas, the Crank shaft pulley problem has kiboshed those plans. You may recall that last fall my other twenty year old car, the 300E had some transmission problems, which meant that I had to use the Miata later into the season than intended. You may also recall that due to time constraints, when the front of the engine was apart I did not actually replace the wobbling pulley, figuring the Miata would be on the road for such a short time it wouldn't matter and it could be done this year. The Mazda was not on the road a short time and it did matter, a few days before the Benz returned from the transmission shop, the pulley and key started their wobbling thing and the whole thing went crappo; no power, horrible banging noise, etc. At the time my fragile nerves couldn't handle two major breakdowns so I parked the Miata, went on holiday, forgot about it, picked up my Benz and motored happily for the winter and spring. But now it's summer and I want some top down enthusiastic shifting for myself driving. The plan right now is to see if the shaft and pulley can be jerry fixed again, or if more dra$tic measures will have to be taken. New engine anyone? Regardless something will have to be done because right now it's sunny outside and the Miata is sitting under a tarp in the garage like some forgotten junk. No one said owning twenty old cars on a budget would be easy.

Crank(y)shaft Pulley Part 2: The Fix

I talked earlier about the crankshaft pulley problem that early Miata's have; the bolt holding the pulley gets loose, the key holding things steady bangs around deforming the crankshaft, the timing starts to get screwed up and the engine becomes worthless. My car was exhibiting some of the symptoms (wobbly pulley, low low-end power) but I didn't know for sure. Well in May at the start of the Miata season it was time to change the timing and accessory belts so while the front of the engine was taken apart I could have a look: bad news the key and crankshaft were badly damaged.

Here's the end of the crankshaft, the slot at the top where the key fits is about one and a half times wider than it's supposed to be from all the banging.

and here's the key that holds things in sync, notice the large extra groove that's not supposed to be there. It's been banged out too.

Looks bad. No hope. Engine is a gonner.

or is it?

I don't know who came up with this, me or my dad, but we decided to fashion a new key that would be wider at one end to fit snuggly into the wide groove on the crankshaft and line up the sprocket and pulley at the other end. Where we were doing the repair they had an assortment of keys from various vehicles, one from a Dodge Ram was wide enough to fit into the wide end of the crankshaft groove, then we had to machine it to fit the sprocket and pulley. There's me using a fine rotary grinder to thin out one end to fit into the sprocket groove.

Afterwards we banged everything together and it all fit tight. Put the car back together and it works. The timing between the crankshaft and valves matches so it has way more low end power. It's a completely different car, a real peppy sports car. You can powerslide all the time and darting through traffic is a cinch. The fix cost nothing because we got that key for free. So if you've got the same problem don't replace your engine, just machine a new key and it will be fine. Oh and the wobble: It appears the wobble is caused by the rubber damper at the back of the pulley breaking down with time. A new pulley should remedy the problem, I haven't gotten one yet (next season) and I'll let you know. So far it only wobbles when the engine bay is hot, indicating it's the rubber breaking down. I was totally stunned that this worked and saved me from getting a new engine. Next year I'll replace the bolt and pulley just to be sure and inspect to see if everything held during this season. Ingenuity eh?