If you are staring at a torn-down engine and wondering what grit emery cloth to polish crankshaft journals you should actually use, you're in the right place. It's one of those tasks that feels a bit intimidating the first time you do it. You're holding the "heartbeat" of your engine, and the last thing you want to do is take off too much material or leave a surface that's going to eat your new bearings for breakfast.
The short answer for most guys doing a garage refresh is that you'll want a range between 400 and 600 grit, usually finishing with something even finer like 1000 or 1200 if you really want that mirror shine. But there is a bit more to it than just grabbing a sheet and scrubbing away. You have to think about what you're trying to achieve—are you just cleaning up some light staining, or are you trying to smooth out some microscopic ridges left over from a previous life?
Understanding the Grit Progression
When you're trying to figure out what grit emery cloth to polish crankshaft surfaces with, you have to think in stages. You almost never just use one single grit. If the journals look decent but maybe have a little bit of "frosting" or light dullness, you might start right at 600.
However, if there's some very light scuffing—the kind you can't really catch with a fingernail but can definitely see—you might start with 400 grit. This is coarse enough to actually "cut" the surface slightly and level out the imperfections. But here's the kicker: 400 grit leaves its own scratches. If you stop there, those scratches can act like a microscopic saw on your bearings.
That's why you follow up with 600 grit. This stage is where the magic happens. It smooths out the tracks left by the 400 and starts to bring back that polished look. For many standard rebuilds, a good, patient polishing with 600 grit and plenty of lubrication is actually enough. But if you're a perfectionist or building something high-performance, stepping up to 1000 or 1200 grit will give you that slick, professional finish that makes you feel good about the assembly.
Why You Need Real Emery Cloth, Not Sandpaper
I've seen people try to use standard black wet/dry sandpaper from the hardware store for this. While you can make it work in a pinch, actual emery cloth is way better for crankshaft work.
The main difference is the backing. Sandpaper has a paper backing (go figure) that tends to tear or crease when you're trying to wrap it around a round journal. Emery cloth has a fabric or cloth backing. This makes it way more durable and flexible. You can pull on it, "shoe-shine" it, and it won't just snap in half.
Also, the abrasive material on emery cloth is usually more suited for metal. It doesn't shed its grit as easily as cheap sandpaper does. The last thing you want is a bunch of loose abrasive sand getting stuck in the oil holes of your crank. That's a recipe for a very short engine life.
The "Shoe-Shine" Method
Once you've decided on what grit emery cloth to polish crankshaft journals, you need to use the right technique. Most of us don't have a professional crank polishing lathe in the garage, so we do it by hand.
The "shoe-shine" method is exactly what it sounds like. You cut a long, thin strip of your emery cloth—maybe an inch wide. You wrap it around the journal, and then you wrap a piece of sturdy cloth or even a shoelace around that. You grab both ends and pull back and forth rhythmically.
Pro tip: Don't just polish in one spot. You want to move the strip back and forth across the width of the journal as you go. This prevents you from creating "valleys" or uneven spots. You want the wear to be perfectly even across the entire surface. And for heaven's sake, don't forget to rotate the crank every few seconds so you aren't just hitting one side of the journal.
Lubrication is Not Optional
Never, ever polish a crankshaft dry. If you use emery cloth dry, it'll heat up, the grit will clog with metal dust almost instantly, and you'll end up with a finish that looks cloudy rather than polished.
Most guys use WD-40, kerosene, or a very light machine oil. Some people even use automatic transmission fluid (ATF) because it has great detergent properties. Whatever you choose, keep the emery cloth soaked. The liquid carries the "swarf" (the tiny bits of metal you're grinding off) away from the surface so it doesn't scratch the journal you're trying to smooth out.
If the oil starts looking grey or black, wipe it off with a clean rag and apply fresh lube. Keeping things clean is half the battle when you're working with these kinds of tolerances.
The Fingernail Test
Before you even start worrying about what grit emery cloth to polish crankshaft journals, you need to do the fingernail test. Run your nail across the journal. If your nail "catches" on a scratch or a groove, polishing isn't going to fix it.
Polishing is for surface finish; it's not for removing metal. If you have a groove deep enough to catch a fingernail, that crank needs to go to a machine shop to be turned (ground down) to the next undersize. If you try to polish out a deep groove by hand, you'll end up making the journal "out of round" or tapered. Once that happens, your oil clearance goes out the window, and you'll be pulling that engine back out of the car in a month.
Cleaning Up the Mess
This is the part people usually rush, and it's the most important part. After you've spent an hour or two getting those journals looking like mirrors with your 1000-grit cloth, you have a crankshaft covered in oil and microscopic metal particles.
You need to clean it like you're preparing it for surgery. Use a good parts cleaner or brake cleaner. You want to focus especially on the oil galleries. Those little holes in the journals lead to the center of the crank. If any emery grit got in there, it will be pumped straight into your new bearings the second you start the engine.
I like to use a small nylon brush (like a pipe cleaner) to scrub out the oil holes, then blow them out with compressed air. Do this three or four times. Then, wipe the journals down with a clean white lint-free cloth. If the cloth comes away with any grey or black tint, it's still dirty. Keep cleaning until that white cloth stays white.
Final Thoughts on Grit Selection
To recap, if you're doing a "freshen up" on a budget: * 400 grit: Only for journals that have visible staining or very light scuffs. * 600 grit: The "sweet spot" for 90% of the work. * 1000+ grit: For the final "bling" and the smoothest possible surface.
Don't overthink it too much, but don't get lazy either. Taking your time with the right what grit emery cloth to polish crankshaft journals will pay off in the long run with an engine that runs quiet and holds great oil pressure. It's a tedious job, and your arms might be sore tomorrow, but seeing that crank shine like chrome is a pretty satisfying feeling. Just keep it lubed, keep it clean, and don't try to "polish away" a major mechanical failure. Good luck with the build!