If you've spent any time in an engine machine shop, you've probably laid eyes on a sioux valve grinder 645 sitting in the corner, likely covered in a bit of oil and metal dust but still looking ready to work. It's one of those pieces of machinery that feels like it was built to survive a nuclear winter. Even though technology has moved toward high-end CNC stuff, these old red Sioux machines remain a staple for guys who actually like to get their hands dirty and understand the mechanics of a perfect valve job.
The 645 model specifically has a reputation for being a workhorse. It's not the newest kid on the block, and it definitely doesn't have a touch screen, but that's exactly why people love it. It's predictable, heavy, and when it's dialed in right, it produces a finish that's hard to beat.
The Heavy Metal Philosophy
One thing you'll notice the second you try to move a sioux valve grinder 645 is that it's heavy. Really heavy. We're talking about solid cast iron construction that was designed back when companies weren't trying to save a buck on shipping costs by using plastic.
That weight isn't just there to make you sweat when you move it; it's there to kill vibration. When you're grinding a valve face, the last thing you want is the machine "chattering" or vibrating. Any movement at the stone or the chuck translates directly into the finish of the valve. Because the 645 is so grounded and beefy, it absorbs those micro-vibrations, giving you that smooth, mirror-like finish that makes an engine builder smile.
Setting Up and Getting the Feel
Using this machine is a bit of an art form. It's not a "set it and forget it" kind of tool. You have to get to know it. When you first get a sioux valve grinder 645, the first thing you usually have to check is the coolant system. These machines use a pump to keep the stone and the valve face cool while grinding. If you run it dry, you're going to ruin the valve and probably glaze the stone.
The chuck is the heart of the machine. The 645 usually features a high-precision chuck that grips the valve stem. You've got to make sure that chuck is clean. Even a tiny bit of grit inside the rollers can throw off your alignment, and suddenly your 45-degree angle is actually a 44.8-degree mess. Taking the time to wipe down the stem and ensure the chuck is grabbing properly is half the battle.
Dressing the Stone
You can't talk about using a sioux valve grinder 645 without mentioning the diamond dresser. If your stone is loaded up with old metal or isn't perfectly flat, your grind is going to suck. Period.
Most guys will dress the stone lightly before starting a fresh set of valves. You swing the diamond arm over, take a tiny pass across the face of the spinning wheel, and you'll see it go from a dark, clogged gray to a fresh, sharp surface. It's a satisfying sound, and it's the only way to ensure the stone is actually cutting the metal rather than just rubbing against it and generating heat.
The Importance of Coolant
The coolant on these old Sioux machines can be a bit messy. It's usually an oil-based or water-soluble mixture that sprays right at the contact point. If you're buying a used sioux valve grinder 645, check the coolant tank. Sometimes they get filled with sludge over thirty years of neglect. Cleaning that out is a gross job, but once you have fresh fluid running through the lines, the machine performs on a completely different level. It keeps the heat down, which prevents the valve from warping while you're working on it.
Why People Still Buy Them Used
You can go out and buy a brand-new valve grinder today, but it'll probably cost you as much as a decent used truck. That's why the market for the sioux valve grinder 645 is still so active on places like eBay or local shop auctions.
The beauty of these machines is that they are almost infinitely rebuildable. The motors are stout, the bearings are usually standard sizes you can find at any industrial supply house, and the belts are easy to replace. Even if you find one that looks like it's been sitting in a damp basement since the 80s, a bit of elbow grease, some fresh oil, and a new stone will usually bring it back to life.
There's also something to be said for the "feel" of the manual wheels. You're the one controlling the feed rate. You can feel through the handle when the stone makes contact and how much material it's taking off. It's a tactile experience that helps you catch issues—like a slightly bent valve stem—before you've finished the whole set.
Common Quirks to Watch For
No machine is perfect, and the sioux valve grinder 645 has its own little personality traits. One thing to keep an eye on is the belt tension. If the belts are slipping, you won't get a consistent speed at the chuck, and that leads to "shadows" on the valve face. It's a simple fix, but it's something that trips up beginners.
Another thing is the oiling points. These machines have specific spots that need a drop of oil every now and then to keep the slides moving smoothly. If the carriage doesn't move easily, you'll find yourself pushing too hard, which can lead to uneven grinds. A well-oiled 645 should glide across the ways like it's on ice.
Is It Right for a Home Shop?
If you're just building one engine every five years, a sioux valve grinder 645 might be overkill. It takes up a decent amount of bench space and it's heavy. But if you're a cylinder head nerd or someone who restores vintage engines, having one of these in your garage is a game changer.
It gives you the freedom to do your own head work without waiting three weeks for a machine shop to get around to your project. Plus, there's a certain pride in knowing you ground the valves yourself on a machine that's probably older than you are.
Parts and Maintenance
Luckily, because so many of these were made, getting parts for a sioux valve grinder 645 isn't a total nightmare. You can still find stones in different grits—everything from coarse stones for roughing in a badly pitted valve to fine finishing stones that leave a polished look.
The diamond tips for the dressers are also readily available. It's worth keeping a spare on hand because once that diamond gets dull or chips, you're stuck. You can't get a good grind with a bad stone, and you can't get a good stone without a sharp diamond.
Wrapping It Up
At the end of the day, the sioux valve grinder 645 is a relic of a time when tools were built to last forever. It's not fancy, it's not digital, and it's definitely not light. But it is accurate, reliable, and honestly, pretty fun to use.
Whether you're a professional machinist keeping an old favorite alive or a hobbyist who stumbled upon a deal at an estate sale, the 645 is a solid investment. Take care of it, keep it oiled, and it'll probably be around to grind valves for another fifty years. There's a reason you still see that iconic red paint in shops across the country—it simply works.