Crankshaft Hub Bolt Loose? Torque spec?, Sigh... Options

[GregAmy]

Is it a known issue for the fan hub bolt to loosen?

Backstory: car started running like hell last Spring on my Microsquirt conversion. Wouldn't rev, #3 CHT going vertical, very hot exhaust. WTF, over? I checked some basic stuff, nothing found.

Drove it again a week later and it seemed to be getting worse. Checked the ECU logs and all seemed normal, TPS, MPS, all working as expected. I even went back to a tune that worked great in November (only difference was cold startup stuff, which I can test/adjust in the Spring when it's colder), but still even worse. Checked timing with an adjustable light at full advance, spot on for what the ignition map was calling for.

I parked the car. Life was busy this year and I just didn't have time to deal with it. But I trotted it out again in September, and it was just as bad. Since I had problems with the IGN4VW coil a year or so ago (mounted in a hot place and was cutting out), I replaced the coil with one from NAPA.

Suddenly the car would not start at all. And when I looked at the ECU logs during cranking, I was seeing 0 RPMs. Bad crank position sensor?

Today I put the car on the lift and visually inspected the crank position sensor (as well as I could, anyway; the toothed gear replaces the A/C spacer) and the spacing of the CPS tip to the teeth was clearly too large; whereas it should be about 50-thou, it was actually around 1/8"-3/16". I pried on the sensor bracket with a screwdriver, and it was solidly mounted, no looseness.

I know I spent a LOT of time getting that sensor set just right during the install (you can't get it it with the engine installed). So I knew something was up. The sensor was solidly mounted, the toothed wheel was not loose, so there was only one thing to check...

..and yup, the hub bolt was loose, allowing the hub to walk outward. Sigh...

I tightened it down - best spec I can find in the interwebs is 23ft-lbs - and of course the car fired right up and drives fine. I hope this didn't cause any other damage...

Is this common? I've never seen it before. The engine was built in California and I truly don't recall who installed the hub, them or me. It's torqued down right now and I'm going to check it on a regular basis (I thought about pulling the bolt and putting Blue Loc-Tite on it, but if I lost that bolt in there then I'd be toast and would have to pull the engine to get it back. Arthritis in the thumbs and tennis elbow so NFW I'm tempting that Fate...)

Oh, and then I broke the door cam actuator when I was putting it back in the garage..it just never ends, does it...? - GA

[Dave97]

I had the bolt come loose on mine a year ago. It all started with replacing the alternator. I adjusted the belt, went for a test drive, made it maybe a mile heard a bunch of noise as the fan became loose. I bought the car with a 2270 motor. Pulled the engine and found not much left of the key and the crank key way on one side looked pretty bad. Now I have a stroker crank that doesn’t look good. I went for it and did the shade tree mechanic repair. I figured that it will turn out to be a total rebuild if it didn’t work anyway.
I got anther hub and new key, then lapped them. The threads in the crank were worn because the fan moved with the loose bolt. I tapped to the crank to the next size. Used jb weld to set the key into the crank. The crank had one good side of the key way. Put the hub on and lock tited the bolt. The one thing I didn’t do and should have was confirm the timing mark on the fan in relation to the engine. Just a little bit off at the hub gets bigger at the mark on the fan. It’s close as I didn’t touch the distributor before and check the timing after and it looks right.
It’s been running for a year now with about 4000 miles. No problems.
Dave

[930cabman]

I had the bolt come loose on mine a year ago. It all started with replacing the alternator. I adjusted the belt, went for a test drive, made it maybe a mile heard a bunch of noise as the fan became loose. I bought the car with a 2270 motor. Pulled the engine and found not much left of the key and the crank key way on one side looked pretty bad. Now I have a stroker crank that doesn’t look good. I went for it and did the shade tree mechanic repair. I figured that it will turn out to be a total rebuild if it didn’t work anyway.
I got anther hub and new key, then lapped them. The threads in the crank were worn because the fan moved with the loose bolt. I tapped to the crank to the next size. Used jb weld to set the key into the crank. The crank had one good side of the key way. Put the hub on and lock tited the bolt. The one thing I didn’t do and should have was confirm the timing mark on the fan in relation to the engine. Just a little bit off at the hub gets bigger at the mark on the fan. It’s close as I didn’t touch the distributor before and check the timing after and it looks right.
It’s been running for a year now with about 4000 miles. No problems.
Dave

Major victory (IMG:style_emoticons/default/piratenanner.gif) "tapped the crank" I wasn't sure this was possible with it being hardened. Must be at the journals only

My gut would have said there is little chance for lasting repair when there is damage.