Loose harmonic balancer bolt?

[pmbrunelle]

So I was installing my new clutch, and I was torquing down the pressure plate.

My dad was at the front of the engine, with a socket and breaker bar on the harmonic balancer bolt to keep the crankshaft from turning.

To our surprise, the 25 lb*ft pressure plate bolt torque was enough to make the harmonic balancer bolt turn.

That M12 bolt is supposed to be torqued in the 66~84 lb*ft range, and I'm pretty sure that's what I did when I assembled the engine about 12000 km ago. I had used medium strength threadlocker.

What could have happened? Perhaps the camshaft drive sprocket or harmonic balancer wasn't seated properly?

A few times, I used the harmonic balancer bolt to turn the engine over backwards, such as to set up the distributor. However, the torque to turn over the engine isn't huge, so I don't think I unscrewed the bolt in that manner, but I'm not sure.

I have bounced off the rev limiter a few times, but only occasionally.

[ericjon262]

the pressure plate bolt is on the OD of the flywheel, so if the torque wrench was radial from the crank centerline, it may have applied much more towards the crank.

[pmbrunelle]

the pressure plate bolt is on the OD of the flywheel, so if the torque wrench was radial from the crank centerline, it may have applied much more towards the crank.

Right... The pressure plate bolt is ~5.25" away from the crankshaft axis.

My torque wrench handle is 15" away from its 3/8" square drive.

My hand may have been pushing at a distance of 15" + 5.25" = 20.25" from the crankshaft axis.

Torque about the crankshaft axis = 25 lb*ft * 20.25" / 15" = 33.75 lb*ft

Still doesn't seem like a lot though. Also the harmonic balancer bolt began turning at some point before I reached 25 lb*ft; 25 lb*ft was just the setting for the click-type torque wrench.

[ericjon262]

the pressure plate bolt is on the OD of the flywheel, so if the torque wrench was radial from the crank centerline, it may have applied much more towards the crank.

Right... The pressure plate bolt is ~5.25" away from the crankshaft axis.

My torque wrench handle is 15" away from its 3/8" square drive.

My hand may have been pushing at a distance of 15" + 5.25" = 20.25" from the crankshaft axis.

Torque about the crankshaft axis = 25 lb*ft * 20.25" / 15" = 33.75 lb*ft

Still doesn't seem like a lot though. Also the harmonic balancer bolt began turning at some point before I reached 25 lb*ft; 25 lb*ft was just the setting for the click-type torque wrench.

that was my best guess. I would torque it back to spec, and then check it when it's back in the car for a bit, it should be accessible through the wheelwell.

[The Dark Side of Will]

I would guess that the balancer wasn't seated correctly... you might torque it to spec without the threadlocker, then check it frequently following return to service. When you get to the point at which it stops working loose, then remove and reinstall with thread locker. There are similar operations with the "Jesus nut" on Blackhawks... Torque to spec, run 10 hours, then check torque.

[pmbrunelle]

The car is still down while I wait for the Cerakote guy to do my heat shields. I also have a cracked transmission mount boss that is cracked; it probably needs to be welded.

Anyway, after torquing the balancer bolt, I decided to mark the bolt and washer with paint, to detect any rotation.

Balancer Bolt.JPG (764.23 KiB) Viewed 981 times

The absence of rotation doesn't guarantee the presence of clamp load, but it's still good info to have nonetheless.

I also marked the outer ring of the harmonic balancer while I had the red touch-up paint out.