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]

OK Master...

Why are SO many high-performance balancers available for the Subaru 4 cylinders?

There's a bunch of different Fluid dampers for them as well.

I cannot remember a Subie with a solid balancer as stock equipment ever.
I've been repairing Subies since the early 80s.
Seen WAY TOO MANY.



I didn't say I was right...

I'm trying to help determine why one member (a freaking knowledgeable one!) has 3 of the same problem.

I'm in agreement with Jeff.

3 is NOT a fluke.

SH, what do you think is the reason for Jeff seeing as many of these as he has?

[Superhawk996]

OK Master...

Why are SO many high-performance balancers available for the Subaru 4 cylinders?

There's a bunch of different Fluid dampers for them as well.

I cannot remember a Subie with a solid balancer as stock equipment ever.
I've been repairing Subies since the early 80s.
Seen WAY TOO MANY.



I didn't say I was right...

I’m no expert expert on Subaru’s for sure but I’ll give you my speculation and what came up with after reading a couple of Subaru SAE papers.


Subaru does indeed call it a harmonic balancer but they don’t say what frequency they are tuning it for. I did find a waterfall plot of their 1st order and 2nd order frequencies and indeed they are much lower than typical 2nd order harmonics from an inline 4 cylinder as would be expected. There does seem the be a weird set of vibrations at 1.5 engine order.



This leads to two points of speculation as to why they have it.

1) It is likely tuned for other engine NVH harmonics coming from A/C, power steering, or something else that would be objectionable to customers? A/C would be the prime suspect since all compressors impart objectionable vibrations on the engine especially at idle. Could these be the 1.5x engine order vibrations that show up in their NVH waterfall plot?

2) the Subaru crankshaft is longer than a VW T4 crank. The Subi is a 5 bearing crank vs the T4 which is effectively a 3 bearing crank (4th nose bearing doesn’t support much). The T4 crank has much thicker webs between journals and it may be a stiffer crank.

So the Subi may have some crankshaft torsional vibration issues as you were alluding to. They also spin the crank to higher RPMs than the T4 and forces go up as the square of crank RPM. Maybe they are using the harmonic damper to damp crankshaft torsional vibrations that the T4 isn’t subject to.

I know VW and Porsche air cooled engines far better than Subaru’s and the only thing I can say is that none of the VW air cooled engines nor the early Porsche 6 cylinders used a harmonic balancer. And the Porsche six cylinder crank is easily as long or longer than a Subi four cylinder. Porsche six’s were similar or higher power output per liter than Subi (naturally aspirated) so it seems odd to me that they would need the harmonic balancer due to crankshaft torsional vibrations related to durability, but the devil is in the details and I certainly don’t have all the details on Subi’s. Perhaps the Subi crank is not as stiff as the Porsche six or VW T4?

@technicalninja

As you elegantly stated . . . I may not be right. I’m always open to be schooled and I’ll keep digging to see if I can better understand why Subaru is using a harmonic damper and what frequency they have it tuned for.