Sheared-off lug nuts likely due to overtightening by air wrench

Dear Car Talk:

Did power tools cause a lot of problems when first used to tighten lug nuts? We were with Mom in the 1972 VW Van and heard a loud clunking on the front passenger side. Mom pulled over, and we removed the hubcap to find one lonely lug nut in place – the rest had sheared off! Was it an overtightening problem? – Theresa

RAY: Probably. Unless it was an ex-boyfriend problem.

It is hard to control the torque (twisting power) of air-powered impact wrenches. And – as you would expect – most mechanics preferred to err by making them too tight rather than too loose. But as you and Mom learned, too tight isn’t so good either. They can be tightened so much that they stretch the lug bolts themselves, and weaken them to the point where they can break off.

You’re lucky you stopped when you did, because those VW Vans didn’t run very well on three wheels. They regularly crossed the country on three cylinders, but not on three wheels.

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Now there are things called “torque sticks” that help prevent overtightening. Each torque stick is rated for a certain amount of torque. It goes between the air wrench and the lug nut. And once it reaches its maximum torque, it starts to slip, which limits the amount of force that can be applied to the lug nut.

Torque sticks work well – as long as the mechanic uses them. And as long as he doesn’t keep hammering away at the lug nut after the stick starts slipping. Our guys often will put a torque wrench on a couple of random lug nuts after they’re tightened, just to check that they’re tightened correctly.

A torque wrench measures how tight the lug nuts are. So if a lug nut is supposed to be tightened to, say, 85 lbs.-ft., and the torque wrench says it took 300 lbs.-ft. to remove it, the mechanic knows that something’s wrong. But we see less of that these days, because we’ve actually switched over to battery-powered tools.

The great advantage of battery-powered tools, at first, was that you could reach into places that a bulky air wrench just couldn’t reach. And you didn’t have to worry about dragging the air hose into these little spaces along with you. But we also discovered that it’s much easier to control the torque on a battery-powered impact wrench.

They’re not perfect. If we come across a lug nut that’s been really overtightened by some animal at another shop (or by one of the animals at our shop), sometimes the battery-powered wrench just doesn’t have enough torque to get it off. Then we have to drag out the air wrench to remove it.

But we use battery-powered wrenches exclusively for lug nuts now. And you’ll be glad to know we haven’t sheared off a lug bolt in days, Theresa!

Valve tightening is unique to Honda, requiring adjustment

Dear Car Talk:

My Honda dealer says the valves on my 2013 Honda Accord should be adjusted. As I write this, the car is about to hit the 100,000-mile mark. Do I really need to pay $150-$200 to adjust the valves? And how come my dealer also says I don’t have to replace the timing belt (not that I’m complaining)? Thanks. – Steve

RAY: Yes, you do have to adjust the valves, Steve. And $150 to $200 is the right price.

This is a problem that seems to be unique to Honda: Honda’s valves have a tendency to get too tight. On most cars, valves get looser over the years and start to clatter. But Honda valves tighten up, so you don’t get any warning noise.

Hondas are prone to something called “valve seat recession” (I’m sure we all remember the great valve seat recession of 2008): The constant pounding of the valves into the valve seats actually drives the valves further into the cylinder head. Over time, that movement causes the valves to tighten up.

The danger is that if you don’t adjust the valves, the valves stop closing completely. Then the hot combustion gases can sneak by a valve and burn the edges of it. We mechanics call that “burning a valve.” Fixing it requires a valve job, which we mechanics call “a boat payment.”

So it’s well worth a couple of hundred bucks to adjust the valves, even though nothing seems to be wrong. And most likely, this will be the only time you’ll ever have to do it. Because by the time this car has 200,000 miles on it, you’ll probably be driving a 2023 Accord.

And the reason you don’t need to replace your timing belt, Steve, is because your Accord doesn’t have a timing belt – it has a timing chain.

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