In repair work, the simplest job is removing and reinstalling bolts (including screws—note, the concept differs and must be clarified). But even with bolts, there are standards, as well as my own exclusive tricks!

Because this topic touches on many details, this note will be updated from time to time. I’ll continue to add content at the end—but remember, this is not advanced technician training material. Don’t set your expectations too high. All of these lessons are from my own experience and summary—not copied from anyone else.

Key rule:
Whenever possible, reinstall all usable bolts back into their original position.

This is a fundamental operation that you will not find in any official service manual or expert training. Yet it’s the most basic common sense a mechanic should know. Ignore it, and small problems can snowball into major failures. This is my single most important conclusion from over 40 years of work. If you want to repair machines properly—at least without making them worse—follow this. Anywhere in the world, no mechanic will tell you this is wrong. At most, they’ll complain it’s troublesome.

On removing bolts:
Depending on the case, some bolts can be removed directly, while others require preparation—otherwise, you’ll face issues like seized bolts, stripped threads, or broken fasteners. Use heat, penetrating oil, etc.

Bolts (including screws) are absolutely indispensable elements in machinery. You’ll notice that on low-end machines, bolts are often only strength grade 8.8 or even 4.8. This is why high-end machines don’t “lose” bolts. Check the grade of bolts on your own machine—you’ll know right away if it’s high-end or low-end.

When I worked at foreign-owned companies, I taught this “original-position” trick to mechanics under my management. At first, they were only interested in learning high-end techniques. Nobody cared about such basics—until they suffered for it. Now, they’ve all learned the importance of this rule. At minimum, when replacing cylinder head gaskets or main bearings, they follow it.

Cylinder head example:
Among average mechanics, you’ll often see them pile all cylinder head bolts together, then reinstall them one by one in random order. That’s amateur work—clearly not trained properly. After my training, my colleagues now punch matching holes in the cylinder gasket package to hold each bolt and pushrod in place—this is what “original position” means.

The principle:
Any reusable part should be reinstalled in its original location (except when intentionally swapped). Because bolts already have an established fit with their threads, swapping them risks damaging the mating surfaces. At the very least, it won’t be better than before. If a bolt goes in hard, that’s usually the reason. Running a tap through the threads may make it easier to install, but it does not restore accuracy—the thread precision is already lost. That’s why support rollers sometimes fall off—it comes back to this. In remanufacturing, thread repair has very strict requirements for exactly this reason.

Mechanics who brush bolts with a wire brush before reassembly are trained ones—they’ve learned it or seen others do it. Why? Because dirt and debris from disassembly cannot be completely cleaned any other way.

Some “shop-floor truths”:

• If you see a mechanic pounding precision parts with a sledgehammer and punch, he probably learned from a demolition worker, not a repairman.

• If you see a mechanic using sandpaper to polish burrs on a scored control spool, that’s a “level-250” mistake. Sandpaper scratches the undamaged surfaces, enlarges clearances, and causes bigger leakage. The valve may not stick, but only because the gap is too big. That’s why machines often run worse after repair.

• If you see a mechanic who never puts down his adjustable wrench—tightening every bolt with it—find another mechanic. That’s an electrician’s habit, not a mechanic’s.

On identifying threads:
There are many thread types. Specs in manuals explain them, but in real repair work, threads of nearly the same diameter but different pitch drive mechanics crazy. Here’s a trick: press the bolt threads into a piece of cardboard or wood, roll it, and compare. You’ll quickly see if the thread pitches differ—avoiding cross-thread damage.

For internal threads, the same method works. Use a small stick, a cigarette butt, or even a piece of chalk—press it into the threads, then compare it with the bolt. No need for a thread gauge.

On installation:
Always tighten bolts in the required order, using the specified torque or angle. After each bolt is finished, mark it with a pen to avoid double work or missed fasteners. This is not my invention, but it works without fail.