Top 5 Over-Torquing Mistakes

1. Anything into Aluminum

They say the stock market runs on only two emotions: fear and greed. We can get greedy when working on our cars, sure, but more often we get scared. Our two primary fears are Fear of Leaks and Fear of Loose. Either one of these can tempt the most reasonable among us to just give it just one extra half-turn. If a little is good, we tell ourselves, then a little bit more must be a little bit better. Aluminum seems to agree with us, it will give us that little bit more, even though it doesn't want to. Don't let fear make you greedy. Don't be what European sports car mechanics used to derisively call "cast iron mechanics." Get familiar with the correct torque specifications for everything on your car and follow them. A few extra lb-ft of torque isn't going to help seal a leak or keep something from loosening—tightness isn't a substitute for good sealing surface prep and can't do the job of retaining systems (Loctite, Nyloks, lock washers, cotters, safety wire, stud elasticity, etc.). If the thoughts running through your head go something like, "let's see if it will take a little more tightening," then you are tempting fate for no reason. You might even have gone past the point of no return and stripped threads out or cracked a casting (see above) in the past, subsequently promising yourself you wouldn't make that mistake again. Listen to yourself. Knowing the correct torque will eliminate guesswork, and fewer guesses equal less fear.

2. Cam/Valve Covers, Oil Pans (tie)

Cam covers and oil pans are really in a three-way tie with carburetors when it comes to warpage due to overtightening, but since carbs aren't the norm anymore we'll focus on the first two. Whether your covers and pans are a thin stamping or an alloy casting, they are just weak metal. Think of hold-down fasteners as being a bed of nails, as opposed to railroad spikes. You want an equal, light pressure on all of them, even going as far as torquing them down in sequence and in stages—like head nuts/bolts or lug nuts. If one nail on that bed is higher up, or if you aren't lowered onto the bed evenly, bad things will happen. Check the flatness of your pan or cover before you bolt it onto your engine. Put your cover/pan on a perfectly flat surface such as a mill table or a surfacing stone, or hold a straight edge up to the sealing area of your piece, and check if you can see light. If you can, measure the gap with a feeler gauge. Gaskets and sealant are meant to seal irregularities but can't seal much of a gap. Your pan or cover will have to be straightened or machined flat again if the gap goes beyond what your gasket is able to bridge. Whatever you do, do not try to seal leaky gaps with an extra generous application of silicone sealant. First of all, it won't work so you're wasting your time. Second, the silicone can tear off or squeeze out and clog vital oil pickups and passages. Don't do it.

3. Anything 8mm

Why 8mm? Because it's human-sized. Humans need a little help to torque a 12mm or a hardened 10mm bolt to spec—like a longer lever—which reminds us we're playing with bigger stakes. Similarly, most people know the importance of using a torque wrench on the cylinder head and main cap fasteners. Us big, strong humans are also aware that we can easily overpower puny 5mm and 6mm threads so we go easy on them. But 8s are friendly. We can tighten them the right amount without too much difficulty. The difficulty enters the picture when we get greedy or scared and go for just a little bit extra. It's way too easy to pull threads out of a casting or, when the fastener goes into something stout, to strip 8mm threads or hexes. Learn the correct torque rating for the grade and thread pitch of your fastener and the application it is designed for—even on something as friendly as an 8mm nut.

4. Exhaust Manifolds/Headers

Flanges are always a problem. They are at less-than-ideal angles from the pieces they seal, and take up too much room or weigh too much if they are beefy. Exhaust flanges are even more problematic than other flanges because of the extreme heat they regularly experience. If they are made from cast iron they crack easily, and if they are mild steel, like headers, they warp easily. Some engineers seek to solve the problem with nice thick compressible gaskets but that adds another level of flex that can cause its own headaches. Ditto for undersize hex fasteners designed to fit in the tight spaces headers usually live. Get ready for some déjà vu: check the flanges for flatness and correct as necessary, do not over-torque in an attempt to seal leaks.

5. Drain Plugs

Is there any greater fear than losing a drain plug and puking all your oil out, seizing your engine uptight? 
Never mind that you're more likely to spray oil out of a failed pressure sending unit that costs 15 bucks than to replace than have a drain plug back out. As long as there are drain plugs there will be over-torqued or stripped drain plugs.  Rather than have a drain plug back out, as long as there are drain plugs there will be over-torqued or stripped drain plugs. It doesn't help that they often have a large hex—just begging for more torque, a large diameter with few threads—the perfect conditions for cross-threading, or are made from or go into soft aluminum—just asking to be stripped. The familiar ingredients apply, even at the bottom of your engine: clean and true surfaces, prudent torque, and fresh sealing devices (new washers in this case). When it comes to your car, remember the wise words of investment guru Warren Buffett: "Risk comes from not knowing what you're doing."

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