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Harmonic balancer

A friend said her car would not crank, so I checked it out and could not find any obvious things wrong, so I told her to take it to Mazda to have her 1999 Miata checked out. I am not new to auto mechanics so I do know a little! So the dealer calls her and said she needed a new engine! WHAT!! So her and I went over there to see what was up! Well it turns out that the Harmonic balancer key had sheared. Well, she had a 60,000 mile service done on the car that cost her 2,000.00 (timing belt) at this dealership. I told the dealer, this was a mechanic error and that they should be the ones to cover this cost. They keep saying that it was mechanical failure of the key and not their problem.
I told them this is a direct failure of a bolt that was not correctly torqued.

Did they have to remove the harmonic balancer to replace the belt? I don’t think so. So probably nothing they did. However, there might be a cheaper fix than getting a new engine. I had a balancer work loose one time and it was fixable. There was around 300k on the engine at the time.

The harmonic damper does not have to get removed to replace a timing belt. Was the front seal weeping? What other than the belt was included in the $2000?

The car is a 1999. Anything is possible. I don;t know on what you’ve made your assumption, but on a vehicle this age anything is possible. Without some basis to blame the shop, I’d be reluctant to. If you can provide more detail, perhaps I’d be convinced.

You can’t remove the lower timing belt cover until the harmonic balancer is removed.


I stand corrected and I thank Tester for keeping me on the straight and narrow.

The key material is supposed to be softer than the materials used in the balancer and the crankshaft, so they should be able to just replace the key. And yes, it was the mechanics fault for not torquing the crank bolt.

Supposed to be and what is are different. I’ve seen numerous crankshaft keyways damaged from loose balancers.

As pointed out above, the balancer was removed during the timing belt service. How long ago and how many miles since the timing belt service?

Even at worst, the car doesn’t need a new engine, just a new or reman crankshaft, balancer, and key. Maybe an oil pump.

Was the keyway damaged? Or was only the woodruff key damaged?
How long ago was 60K service/timing belt done? If less than a year, the shop should usually warranty the parts and labor for a year.
I’ve done my fair share of timing belt jobs, including on older cars with fairly high mileage.
And I’ve not had a damaged key or keyway yet. Just saying . . .
I have seen plenty of damaged components caused by insufficiently tightened hardware . . .

Yes, the harmonic balancer mjust be removed to change the timing belt, at least it’s required on my Corolla, which is probably similar to the Miata configureation. I don’t see this as being a “new engine” situation. I expect a good auto machine shop could solve this, possibly wouldn’t even require removing the engine. In any event, no harm done to ask several auto machines shops for repair quotes before buying a new engine.

If the balancer was loose due to an insufficiently tightened bolt, the constant vibration (which may not be noticeable to the driver) can eventually peel the Woodruff key out and damage the keyway in the crankshaft.
I’ve seen several incidents like this and it always boiled down to someone not tightening something properly.

The only way the key should shear would be if there was a major league seizure of an accessory such as an A/C compressor, etc. and even that is a bit iffy because odds are the belt would break before the key gave up.

If all accessories and so on turn freely then someone screwed up the timing belt job. I assume the service manager is the one you talked to and most of them know very little about mechanicals anyway.
The SM no doubt gets a commission each month and he’s reverting to Cover His Hiney mode to make sure the shop is not footing the bill along with guarding his paycheck.

Well, I don’t think I’ll ever buy another vehicle with a timing BELT!!

If the vehicle has a timing chain, and it wears out, the harmonic balancer has to come off.


Tester, you are right, but usually not at 60k.