Top 5 Commonly Overlooked Cleaning Cautions
Spend a few minutes checking each of these and save yourself hours of misery down the line.
Internal Threads
We're assuming for the purposes of this discussion that your threads aren't stretched, stripped, or missing—in those cases, you'll need to repair them and that's a whole different discussion. But just because whatever you are fixing came apart easily enough, it doesn't mean you can just throw it back together. That goes double if your parts needed some coaxing to come apart in the first place. That goes triple when working with steel bolts/studs (fasteners) that thread into aluminum or magnesium (because steel reacts with those metals more readily than it does with cast iron), or when your internal threads are open to water (either by design or due to a casting core shift). Internal threads are harder to see and harder to clean than external threads, so they frequently get neglected.
To ensure you don't damage internal threads you have to make sure the condition of the fasteners you are threading into them is good as well. If you aren't using new fasteners, then make sure the originals are still in good condition and not corroded or distorted, and, of course, clean. If you had to media blast your old hardware, and it resulted in your threads having a rougher texture, then burnish them on a wire wheel so they are smooth and won't abrade your internal threads. After thoroughly cleaning internal threads—unless the casting is designed for an interference or size-on-size-fit stud—do a test assembly by running the fastener down into place, very lightly lubed to prevent galling, just to check the internal threads for feel. The fastener should fully thread into place without any difficulty. If it doesn't, and you've inspected the threads to make sure they are clean, then you may want to use a thread chaser to clean up any corrosion, or scratches/nicks, that are preventing easy assembly. If the fastener still doesn't thread in easily, you may need to run a tap down the threads to remove any stubborn debris or corrosion, while being careful not to remove any of the original threads. We could write a whole manual on using a tap, but the basics are: use cutting oil, clear debris out frequently as you go, keep it absolutely aligned with the bore center (using a jig/mill if necessary), and never ever force it, because you'll snap the brittle tap off and then you are in a world of hurt. Cleaning and test assembly will always take extra time but it can save you hours of anguish from a bolt that got stuck halfway in, and then either tore out threads or snapped off when you tried to pull it back out. Be kind to your metal.
Oil Passages
Like internal threads, oil passages aren't easy or fun to clean out. They're often hard to get at, and always hard to see inside of. Even if you had an item cleaned in a chemical/hot tank to remove every trace of crud, you still have to check it. Sometimes a tank will have used-up chemicals, a bottom full of gunk, or a lower active agent level than you expected. Sometimes cleaning tanks will loosen sludge, but leave it inside of your part. Almost all oil passage bores will have a plug of some kind, and to make sure the bore is completely clean you are going to have to remove the plug, even if you have to drill the plug out and then reseal it again before assembly. Like we said—not fun, but way more fun than having oil-starved bearings seize up at an event you just drove halfway across the state to get to. Run a drill down the smaller-diameter oil passages and a stiff bore brush down the main oil galleys. Especially important are the oil passages in your crankshaft. Baked-solid oil and sludge can be as hard as pencil lead and can't be just washed out by flushing your crank with solvent. If you're not 100% certain something is clean, your job isn't done.
Oil Filter Inspection
You might have seen videos of blown engine autopsies, where they cut open oil filters in an effort to find evidence of some fatal failure. Doing a check-up can save you the heartbreak of having to perform an autopsy in the first place. Cutting open your oil filter after the initial run-in of a new build or mod is an important step, even if everything seemed great and sounded even better. Not only will it tell you if you have really big problems (like when you find metal shavings, flakes, or particles in the filter), but also if you missed something smaller but still worrisome, like rag lint, blasting media, or errant silicone sealant. Especially silicone. Many sins have been committed in the war against leaks.
Media Blasting Residue
Speaking of media blasting—there's no free lunch. Media can rid your metal of ugly and damaging corrosion in minutes, however, it can put ugly, damaging scratches in your bearings and cylinder walls just as fast if left behind. Before you blast anything—whether it be with glass bead, soda, shot, or any other dry media—make sure the part you are blasting is completely free of oil, grease, and anything else that's remotely moist, because that moisture will grab and hold blasting media, and make it hard or impossible to blow the media off of the parts with compressed air when you are done. It's best to plug (silicone rubber plugs work well) or otherwise mask off any passages that would be difficult to clean media out of. And when you're done, it's important to wash the whole piece all over again and inspect it closely. Rough castings, moisture in the air, and static electricity have a way of holding media on a certain part even after you've blown it off it with compressed air. Make sure to probe hard-to-reach areas with a pick or other tool, and visually inspect everything. Rotate the piece when you are blowing it off to make sure a pocket of media isn't hiding anywhere. Bodies at rest tend to stay at rest.
Clean New Parts
Nothing is clean unless you cleaned it yourself, twice. Even if it looks perfect and comes in a slick new sealed-plastic package, it's not clean. New parts sometimes have a protective film on them, which attracts dirt. Other parts are covered in mold release residue or a thin layer of machining oil. Your shiny new braided steel lines might have the odd foam packing peanut hiding inside them—it happens. If your parts come assembled, take them apart and check to ensure everything is squeaky clean. And always, always, clean anything you got back from the machine shop. It might look perfect on the outside but your machinists would go broke if they spent time cleaning every part they touched, so it's probably loaded with dirty cutting fluid, chips, and/or honing and grinding grit. If there's a common thread to all of these tips it's to check, check, and check again. Never assume. Because we all know what happens when you assume.
For help with service of your car, check out the how to section of LS1Tech.com