Loose Harmonic Balancer Bolt

About 15 months ago the Toyota dealer replaced the timing belt on my 99 V6 4Runner. About 6 months ago I occasionally began getting a flashing check engine light at highway speed suggesting a random missfire. Gas mileage was also down a bit and idle was a bit rough. The dealer replaced an ignition coil and that did not solve the problem. Just recently I asked the dealer to change spark plugs and check whatever else could cause the problem. This time they found that the harmonic balancer bolt was loose. Strangely, they did not charge me to change the plugs and tighten the bolt. Sounds like the bolt was not tightened properly back when they changed the timing belt.

Does anyone know if there is a chance that something might have been damaged by not tightening the harmonic balancer bolt properly? It seems to me that the Toyota dealer might be trying to hide someting since they did not charge me for the service. Should I have another mechanic inspect the harmonic balancer?

The dealer probably forgot to torque the harmonic balancer bolt. I would have the bolt re-torqued by a mechanic just to make sure. A loose harmonic balancer can wobble and mess up the crankshaft. For peace of mind let another mechanic torque it again.

One type of damage that can happen if the harmonic balancer bolt is loose is that the HB hub wears and the key and keyways in the HB hub and crankshaft nose wallow out. So the HB and crankshaft should be inspected to see if there is damage to the key and keyways as well as fit of the HB hub to the crankshaft nose.

It is interesting that the ECM would pick up the loose HB from the crankshaft postion sensor signel. I am wondering if the HB holds the crankshaft pulse wheel steady on the crankshaft when it is tight. The signel variation may be the result of a wandering loose pulse wheel due to the loose HB. Just a thought.

Thanks for the feedback. Apparently under the right conditions, load & rpm, the crankshaft position sensor can interpret a loose HB as a missfire. The Toyota dealer tightend and re-torqued the bolt and said it should now be OK. Not sure that they really checked for damage.

Based on your comments, I will probably have another independent mechanic look at it to make sure there is no damage. At the moment the vehicle seems to be running fine so hopefully there is not significant damage. I expect that if there was some significant damage I would notice noise, rough idle, etc.

It probably would not make noise or cause roughness until the bolt loosened up again. If there is enough slop to allow the crankshaft to transfer vibration to the bolt instead of the damper, it is possible for the bolt to work its way loose again. So keep an eye on it.

Good luck on this.

an additional point to keep an eye on, is the forward oil seal. I am not sure on the v-6, but on the 22r it rides on the harmonic ballancer and if the HB was loose, it could add to wear or distorion of that seal. A drop of non-hardening lock tight on the retaining bolt would not be a bad idea either when you have it re-torqued.

It turns out that I am now getting a knocking noise when the engine is warm and at idle. It is much less noticable as soon as the rpm is increased above idle. I am wondering if this could be a sign that the harmonic balancer is bad. I did not hear this noise before the dealer tightened the harmonic balancer bolt. I also have heard that this type of noise might come from a bad timing belt tensioner. Any thoughts?

Earlier models have been found to have severely damaged keyways that were apparently caused by stretched timing belts that developed an harmonic slap in the timing belt slack. I suspected that the crankshaft keyway was not properly hardened for such damage to occur. The crankshaft bolt on one truck had repeatedly worked loose and was the cause for it being brought to me. The bolt would likely never work loose if properly tightened and even the weakest thread locking compound used. You might be wise to get a second opinion. It is very difficult to do more than speculate here. I can’t be certain of the cause of the damages that have been repaired on the 3.0 cranks repaired here.

Took the truck back to the stealership today because of the loud rattling noise. Turns out they never removed the harmonic balancer to check for damage after finding the bolt loose. They simply tightened the bolt and told me everything was OK. Today they removed the harmonic balancer and found that the crankshaft gear is worn and they are replacing the gear, keyway and a tensioner pully at no charge. They claim that there is no damage to the crankshaft the thrust bearings. Hopefully this will take care of the problem and will not lead to future problems.

Key point to all who read this – I you find that your harmonic balancer is loose always insist that it be removed to inspect for other damage.

Good, you kept and eye on the harmonic balance and the bolt. Got it fixed at the first sign of noise.

Good work!!

I am somewhat skeptical of the situation, gwb. It would seem advisable to keep all the records on this problem and if the noise reappears any time soon return and ask that the harmonic balancer and the timing belt pulley be pulled for you to inspect the crankshaft keyway.