My turn - Miata crank fix

My Locost has been showing signs of the short nose crank problem. It's part of why it got parked several years ago, and my attention turned to the MG and the Targa Miata. Well, it was time to have a look...

Yup. I'm in the club. The crank bolt came out really easily, so I suspect it was loose. This car has a fairly aggressive set of cams, so low power below 4000 rpm is to be expected. I found out about the problem when the front pulley started wobbling enough to throw the water pump belt at 7000 rpm.

I've got a good shortnose crank sitting right beside the car. But I've decided to try the Loctite fix. I've never actually done it before, so why not give it a try? At worst, I'll just yank the engine and replace the crank later.

Some guy wrote a book with instructions in it a few years back. I think I've got a copy here somewhere...

Keith Tanner wrote: Some guy wrote a book with instructions in it a few years back. I think I've got a copy here somewhere...

You're way too modest

Let us know how it turns out.

I'm guessing the guy who torqued the crank bolt the last time probably knew what he was doing, any idea what caused the failure?

One would hope he knew what he was doing

There should have been loctite on there as well as the proper torque. But I don't think I've been into the engine since just after the Atom test, so that would be around 2007 or so. Not sure what happened exactly, I want to get some undamaged parts in hand and take a good close look at them to compare. The key looks awfully short, although it was oriented correctly. There was a lot of what looked like rust on the threads, but it may have been disintegrated pieces of crankshaft and woodruff key.

Keith Tanner wrote: One would hope he knew what he was doing

If he didn't, that book you're looking for isn't going to be much help

Keith Tanner wrote: There was a lot of what looked like rust on the threads, but it may have been disintegrated pieces of crankshaft and woodruff key.

Could that "rust" be disintegrated locktite? I've seen old locktite be red and gummy, but not what I would call "rusty".

Actually, now that I think about it - I've never had that bolt off. It was probably installed when the engine was built in 1999. At FM, but before my time.

It's not old loctite, this is debris. It makes sense, all the material that used to be in the keyway had to go somewhere.

My bolt came off really easy. We didn't pull the timing belt pulley because the keyway and slot looked good.

New bolt with blue loctite, new crank pulley and OEM bolts with blue loctite and it still wobbles.

I figure it would take me 3 hours to pull it all apart and try again, or about 5-6 to swap engines. I'm hoping I can find a deal on a long nose crank 1.6

I did the bolt, pulley, and key.

Cranked her down beyond the recommended 85...and beyond the recommended 104....and settled at about 115ft/lbs.

I've still got a wobble, but as long as it holds timing and the belts are flinging off, I'm good to go for awhile. I've been beating it pretty good, too.

It's quite possible for the keyway to be fine but the accessory pulley wobbles - depends on the accessory bolt. Since this car is almost exclusively used at 8000 rpm on the racetrack, I'll be sticking a bit closer to the recommended fix. No overtorquing. Given the car that it's in, it'll only take about 20 minutes to do the fix - there's nothing in the way at all. Don't even have to take off the valve cover...

Keith Tanner wrote: It's quite possible for the keyway to be fine but the accessory pulley wobbles - depends on the accessory bolt. Since this car is almost exclusively used at 8000 rpm on the racetrack, I'll be sticking a bit closer to the recommended fix. No overtorquing. Given the car that it's in, it'll only take about 20 minutes to do the fix - there's nothing in the way at all. Don't even have to take off the valve cover...

Wait, are you saying it could be the alt puller or water pump that would make the crank pulley wobble? Even with a new bolt and a new crank pulley and new crank pulley bolts?

Ultimately the wobble isn't the problem, it's the changing timing. Many folks have had the rubber in the drive pulley fail, resulting in lots of wobble, but a perfectly fine crank keyway.

Exactly. The accessory pulley (ie, the damper) is bolted to the timing belt pulley. If the latter wobbles, so will the former. But it's possible for the damper to wobble all by itself.

I've got video somewhere of the damper rotating independently of the crank. There's a timing light on the engine and you can watch the marks walking around the pulley...

I understand the timing issue, I just don't understand why mine is still wobbling. The keyway looked good (granted the timing belt pulley was still on), so we did a new bolt tightened to 85lb ft, then installed a NEW crankshaft pulley with NEW bolts with Loctite and it still appears to be wobbling.

So frustrating.

Wobbling how much? It's not that unusual for one to have a little bit of runout, maybe 3/16".

Keith Tanner wrote: Wobbling how much? It's not that unusual for one to have a little bit of runout, maybe 3/16".

Hmmm, it might be about that much.

What every happened to this motor long term? I'm curious because I prefer the short nose motor for Spec Miata racing due to its slightly lighter weight.
As a side note, I have a long nose '91 motor in my garage that had it's crank bolt come loose too. I think the crank bolt torque on that one should be 120 lbs.

A friend of mine used to call it "the lightweight sport crankshaft".

It's not a motor that sees a lot of use. It's been up to 8000 rpm multiple times since, but not a lot of hours. I've sold the car and it's starting to see more regular use, but it'll always be a track toy.

Keith, I've also heard the blocks where also a bit lighter in the earlier cars.
Any truth to that? Urban Spec Miata legend?
I had a motor built by Mike Rossini last year and it's an absolute screamer.

The vintage guys in SVRA created the Spec Miata Heritage Cup this year and we had over 20 cars at Mid-Ohio. I hope the new series revive's the market for our older cars.

In reply to fornetti14:

I have a 1990 engine, about 95,000 miles. The keyway is fine, but you would need a new bolt and key, and I think the lower cog as I stole them a while back for another car, and I'd sell it cheap!

Pm me if your interested

I have never heard anything about lighter block weight, but SM guys are a little weird.

In reply to joey48442:

Just sent you a PM

fornetti14 wrote: In reply to joey48442: Just sent you a PM

Hmm, nothing came through? Try joeljblatchford @ yahoo dot com