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

[930cabman]

Ouch

Any idea how long this had been loose?

Think this item will go on my list of winter projects, check and double check the taper fit

[GregAmy]

Any idea how long this had been loose?

Just a wild-assed guess, but "not long at all". My fuel logs indicate I've driven it only about 400 miles since October 2021 (not a typo)...

The engine was rebuilt in November 2020 by a company out west, and I installed it over that winter. Fuel logs indicate that was roughly 2,000 miles ago. Most of the miles I put on it since were in 2021.

I seem to recall hearing a light banging noise from the front of the engine earlier this year or maybe late last year, but it went away off idle. Since I had installed a crank position sensor toothed gear behind the fan pulley when I installed the rebuilt engine I thought ok maybe I didn't tighten the fan? So I actually stuck a socket in there to check those bolts but they were fine...but I didn't think to check the hub bolt since I had not removed it since the engine rebuild; there was no reason to.

How long was the bolt loose? Anyone's guess. But with two o-rings stuck in there, maybe it wasn't even tight when I got the engine (or maybe the crushed o-rings affected the torque). I don't recall if I ever checked it.

I'd suggest it was a major failure of imagination on my part for continuing to drive the car once I heard that light knocking happening, and I should have parked the car right then and there to investigate it. That's my fault.

I'd also have to offer that, absent the cranked tooth gear getting massively off time causing the engine to basically stop running, it's quite possible I'd still be driving it anyway.

What a mess. We'll see if we can repair it. Otherwise I think the car will have to get stored somewhere long-term, as I recently got laid off and I have no desire, money, or patience to pay for a replacement crankshaft and new engine rebuild.

We'll see what happens. Fingers crossed. - GA