What do dairy farmers and motorcyclists have in common? 

By: Ari Henning Courtesy: Revzilla

Magnets, meant to ensure the health of our assets. By that I mean cow magnets and magnetic drain plugs, both of which are supposed to grab ferromagnetic crud and keep it from getting places it doesn’t belong. In the cow’s case, that’s nails and bits of barbed wire it accidentally scarfs up with hay. The magnet traps stuff in one of the cow's stomachs — they have four — so it doesn’t travel further along in the digestive tract, where it can be deadly.

Cow magnets work, and so do magnetic drain plugs. If you use one in your engine it will have a coating of slimy fuzz on it at your next oil change. The schmutz it collects is normal wear particles shed off stuff like your primary gear, transmission gears, and piston rings.

The real question is, does getting this gunk out of your oil matter, and do you need a magnet to do it? Well, manufacturers don’t seem to think so, or else they would install magnetic drain bolts at the factory, and only a few of them regularly do. (Here’s looking at you, KTM and BMW.) Most bikes with a driveshaft have a magnetic drain plug for the final gear case, but that’s because there’s no filter to help keep the gear oil clean. 

our engine, however, does have a filter, and it’s pretty efficient. The average oil filter has an absolute micron rating of 30 or 35 microns — for reference, human hair is about 50 microns in diameter — which means the filter will remove anything bigger than that. That includes magnetic alloys, but also non-ferrous stuff like carbon, clutch material, bits of gasket, aluminum, bronze, and other particulates that aren’t swayed by a magnetic field. 

But, what about the steel particles that are smaller than 30 microns? That’s where the proponents of magnetic drain plugs get excited, because a magnet will snatch up any steel bits, regardless of size. And as it turns out, it’s the really small, like one- to 10-micron stuff, that’s the most destructive. 

These “Clearance Size Particles” are small enough to fit into the spaces between parts like your piston rings and cylinder walls, wrist pin, and rod bearings. Plus, steel is one of the hardest substances sloughed off inside your motor, so it’s potentially the most damaging. And if removing it is as easy as putting a magnet in your sump, then why wouldn’t you?

When it comes down to it, a magnetic drain plug is an added layer of protection, and based on the sludge I’ve wiped off magnets, they seem pretty effective. It’s not something all manufacturers think is necessary, obviously, but as an owner you might feel it is. Plus, magnetic drain plugs are cheap and easy to install. Some even come cross-drilled for safety wire, which is great if you’re prepping a bike for the track or racing.

However, there’s something you need to look out for, even with something as simple as a drain plug. Lots of them are made out of aluminum, which is nice because it’s lightweight and you can get them in all sorts of fun anodized colors. However, I’ve seen plugs improperly advertised as being machined from billet aluminum, which is strong and durable, when in fact the bolt is machined from a cast part, which is inherently brittle. The result? Snapped-off drain plugs, well before the recommended torque has been reached. 

A sheared-off drain plug is a real drag, but you can avoid it by not buying cheapo no-name parts off Amazon. Get something from a reputable brand, or better yet, get a steel magnetic drain plug. And of course make sure the thread pitch of your new plug matches your stock one. A 12 mm x 1.5 and a 12 mm x 1.25 bolt seem awfully close, but they’re not the same.

The last nit I’ll pick about magnetic drain plugs is that they’re not in a great spot to do their job. They sit at the bottom of the sump, where the oil just kind of sloshes around. To really be effective, the magnet needs to be directly in the oil flow, which is why I run a magnet on my oil filter. Donut magnets sit right on the oil filter, so the engine oil flows over it and the magnet can snatch every errant particle. Donut magnets work on spin-on filters as well as cartridge filters, and they’re a lot more effective than drain-plug magnets. 

But hey, if you’re serious about protecting your engine, run both!

By: Ari Henning Source: Revzilla