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

[ClayPerrine]

This same thing happened to Betty's car 35 years ago in a little town called Copperas Cove, Texas. We were in town for an AX, and on her last, best run, the engine spit the fan into the shroud. She always said it was because of the lightened load on the engine gave her more HP to the wheels! (IMG:style_emoticons/default/biggrin.gif) (IMG:style_emoticons/default/driving-girl.gif)

Turns out the bolt holding the hub onto the crank broke. So, with the help of a local auto parts shop owner, I got a wodruff key and a new washer and bolt, plus some locktite. I then took the hub off the fan, and put it back together. No crank polishing, no checking it, nothing. We had to drive home that day to be at work the next day. So It was a "field expedient" repair. One of the "repair" techniques I did was to use a brass hammer to drive the hub onto the crank before installing the bolt. That way I wasn't pulling against the bolt to install the hub.

The damn thing stayed on the engine for another 5 years before I had to remove it to replace the seal. And it was a bitch to get back off when I did.


Good luck in your fix!

[Superhawk996]

One of the "repair" techniques I did was to use a brass hammer to drive the hub onto the crank before installing the bolt. That way I wasn't pulling against the bolt to install the hub.

The damn thing stayed on the engine for another 5 years before I had to remove it to replace the seal. And it was a bitch to get back off when I did.

(IMG:style_emoticons/default/agree.gif) This

Though I generally don’t want to be hammering / impacting main bearings you get the point.

It should be a a bear to remove it after a proper install with well matched tapers.

(IMG:style_emoticons/default/smash.gif) (IMG:style_emoticons/default/welder.gif) (IMG:style_emoticons/default/smash.gif)

After the install, the bolt is doing very little to hold the joint together.