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

[GregAmy]

Still ongoing. Using a dental pick I realized the very bottom part was solid (it's anaerobic, after all) and the key was supported so I put in the o-ring and crank seal for final install. Then as I was taking it out one last time for inspection (Shroedinger's o-ring) the key came out with it, along with some of the upper part of the 660.

Visual inspection showed that the bottom part of the 660 was still there and when I put the key back in it was well-supported, no movement. I slipped the hub on and there was no more side-to-side movement. So I packed the top of the space with "JBWeld Steel" and I'm going with that. It'll be reassembled today.

New spark plugs, fresh valve adjustment (love me them zero-lash chromoly pushrods) and I'll get the whole thing leisurely installed this week/end.

What did you use as an abrasive?

Loctive Clover 150 grit lapping compound, then a follow up with 280 grit lapping compound. Got plenty left if you need some...

Would love to see that lapped down to 400 or finer....Assume you did use primer too?

Thought about going higher than 280 but honestly I think this will be fine. I guess we'll see.

Did not use the primer as I couldn't get it within a reasonable timeframe.

You might want to make sure that the hub doesn’t bottom on the crank face before the taper is fully engaged.

It's not; you can see how far up the lapping compound was grinding on the taper and there's a lot of space left. And when I test-fit the hub with the bolt torqued down the or-ring wasn't over-compressed.

I do kinda wish that I had measured the distance from the end of the hub to the nose of the crankshaft; I'm curious how much farther in all this cleanup and grinding allowed...