Harmonic Balancer keeps falling off

astro
chevrolet

#1

We have a 1996 Astro van with 268,000 miles on it. Recently we rebuilt the top half of the engine and ever since that time our harmonic balancer has fallen off and belts and bolt. First came off when starting down echo summit in Sierra mountains above Lake Tahoe. No power steering or brakes on winding road and a sheer drop off on our side of the road. Want to feel your muscles get real strong real fast ? Try that one.



So, way won’t the bolt stay on?

It has now come off 3 times and it was put on twice by mechanics. Help.


#2

Have the crankshaft bolt removed. Apply the blue LocTite thread locker to the threads, reinstall the bolt and torque to specs.

Tester


#3

We have used red LocTite however no one has used a torque wrench to specs. Could that make a difference? The mechanics who twice replaced it just said “get it tight and it will stay”.


#4

If you don’t use the proper torque spec it can stretch the threads on the bolt. And since it’s a softer material than the crankshaft threads, it won’t stay tight. Remove the bolt, throw it out and install a new bolt with the thread locker.

Tester


#5

“get it tight and it will stay”.

Worst piece of advise I’ve heard in a long time. This single bolt holds the harmonic balancer and accessory pully(s). It also holds the timing chain sprocket to the crankshaft. This is a BIG hunk of rotating metal.

The bolt needs to be torqued to spec in order to hold. Torque to spec stretches the bolt, and that stretch puts tension on the threads that hold it in position. Torque too light, and the bolt will work it’s way loose. It’s that simple. Loc-tite is not a substitute for torque. Plain and simple.

The proper torque for this bolt is 74 ft-lbs. You need a torque wrench to know what that feels like. This is not simply tight.


#6

I don’t suppose that you can reach that bolt without taking parts off? If you can, buy a torque wrench and appropriate socket and torque it to spec yourself. Then check it periodically until you are confident that it is staying put. If it isn’t staying put, buy a new bolt.

(Parenthetically, the harmonic balancer on my 1989 Mazda 626 was held on by six relatively tiny 10mm bolts that didn’t require force-majeur for removal and installation. Seems a much more satisfactory design. Why don’t more vehicles use it?)


#7

The crankshaft and balancer may be damaged and wobbling. That movement could be causing the bolt to back out. Remove the balancer and inspect for damage. Look for taper on the crankshaft and damage to the key/keyway.


#8

Good points.

If it were my problem, I’d throw out the old bolt and replace it. Chase the threads in the snout to remove all traces of the old loctite. Use crocus cloth on the snout and inner mating surface of the balancer and then a spritz of B’Laster just to make it slide even better on install. Torque to specs. Remove all spark plugs. Install magnetic base dial indicator and measure runout on both the face and outer circumference (while rotating by hand) just to be sure it’s not wobbling. Periodically re-check bolt until confidence restored…


#9

BTW, what and how is the ‘top half’ of the engine rebuilt?


#10

I’m in agreement with Rod Knox about a loose balancer and wallowed crank nose; especially after 3 times.

Some questions I might ask.
The balancer came loose 3 times and was replaced twice by mechanics. Who removed and installed it during this rebuild and replaced it the first time it came loose?

This was one of those in-chassis rebuilds, and on a quarter million miles+ engine no less?
As to this rebuild, who done it?