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]

Ok, seems I can't quit you...

I was cleaning up the garage yesterday from the mess I made with this project. Came across the old pulley hub (with its slice of key still in the groove) and decided to add it to my "wall of shame" of failed parts I have (when you get into racing you tend to collect stuff like this).

On the shelf, I picked up the broken crankshaft from 2019(?) and was going to slide the hub on there but the crank still had a key in it; I tapped the key out and noted that the key was damaged, offset like the old offset keys we used to use on VW overhead cams for timing. And there were scuff marks on the downstream side of the crank nose where its pulley was chattering.

So that engine's pulley was loose, too. I don't know if that was related to the crankshaft failure, but this certainly caught my attention.

I put the race car on the lift and checked its crank bolt - that engine uses a Bus fan and shroud - and that bolt, too, was slightly loose, about 1/16 of a turn to get it to 23 ft-lbs. So I removed the bolt, loctite blue'd it, and reinstalled to 30 ft-lbs. And I know who built that engine and I know he would not have missed something like this.

One time is random; twice is coincidental; three times is a trend. I think we have a trend going on here. I certainly seem to...

Does anyone know the class of bolt that's being used here? The markings on it are not standard. If it's equivalent to a 10.9 then most charts are showing in the 40 ft-lbs range. The underside of the bolt has locks similar to a Schnorr washer, and I'm sure the engineer didn't want that taper to get hammered in too tight (it would be a bitch to get loose).

However, I noticed all three crank washers have a circular groove where those locks have dug in; if that groove is too deep then the locks may be making less grip contact. Are these supposed to be single-use bolts and washers?

Maybe I'm overthinking this thing, but I've now experienced three potential failures, just in my own garage. So I'm'a thinking that proper torque, Loctite Blue, and maybe new bolts and washers is in order here. And maybe a higher torque value.

Has anyone else checked theirs? What have you found? - GA

[Superhawk996]

I'm sure the engineer didn't want that taper to get hammered in too tight (it would be a bitch to get loose).

I think you’re missing the principle of how a taper works.

It MUST be tight fitting. It should be so tight that it requires a pulley puller, some heat, and a few brass hammer bangs to remove the hub after it has been installed.