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

[technicalninja]

I will put my $5. on they were never properly fit, checked for a high percentage of contact and torqued correctly.

(IMG:style_emoticons/default/agree.gif)

You BEASTS!

Just throw Greg under the bus will ya! (IMG:style_emoticons/default/ar15.gif)

Greg, always remember, I'll have your back!

The hawk and the cabman are subversive...

Now for serious:

SH- I'd be a pissed off engineer if the NVH resonance graphs were taken with ANY accessories running at all.

Subaru has almost exclusively used either vane style compressors (exactly like a mechanical air pump-just sealed up better) or scroll style compressors.
Both designs do not have reciprocating pistons and are super smooth in operation.

I may use a small scroll for a retrofit in a 914 mainly for the smoothness and lack of cycle torque change. If you are forced to use a cycling compressor the scroll design (which is supposed to be the most efficient) has almost zero engagement torque.
It's damn hard to tell when it engages. Often no idle compensation is needed.
I've kept 3 baby Subie scrolls (dead ones) as test fitters.

Subie compressors are probably not a source of serious NVH noise...

I do have a question. You mentioned EARLY 911 motors did not have harmonic balancers. Does this mean later ones do?
If so, when did they arrive?
What other changes occurred along with the balancer?

Balancer is really not what this device should be called.
Vibration shunt or eliminator sounds better in my book.


Ya'll be easy on Greg now...

[Superhawk996]

I do have a question. You mentioned EARLY 911 motors did not have harmonic balancers. Does this mean later ones do?
If so, when did they arrive?
What other changes occurred along with the balancer?

Balancer is really not what this device should be called.

Not sure when later engines got a harmonic damper and/or which variants get it. Modern build complexity is beyond belief. What engine variant, PDK vs manual, dual mass flywheels vs single mass light weight flywheels, 993, 996, 997, etc. (IMG:style_emoticons/default/barf.gif) Late model 911 stuff isn’t my thing.

The proper engineering term is tuned mass damper.

@technicalninja