If you’ve ever stood in a machining shop and watched a connecting rod roll off the line, you’ve probably seen this one super important step that almost no one talks about at first: honing. I’m John, been running a connecting rod machining shop for 12 years now, and I swear honing isn’t just a “fancy smoothness step”—it’s the thing that makes a rod go from “okay” to “actually works in a high-performance engine.” Let me break this down like I explain it to new machinists who walk in here thinking all surface work is the same. Connecting Rod Machining
First, let’s get one thing straight: connecting rods have a brutal job. They connect the crankshaft to the piston, right? So every single time the engine fires, that rod yanks and pulls at like thousands of pounds of force. If the surfaces at the big end (the part that fits over the crank) or small end (the part that holds the piston pin) are even a little off, that force doesn’t spread evenly. It turns into tiny hot spots, or micro-cracks, or even worse—seizing mid-race. Honing fixes that in ways no other machining step can. A lot of shops mix up boring vs honing, and that’s where I see their rods fail before they even hit the customer. Boring’s the rough cut to get the hole the right size. Honing’s the last touch that turns a “round enough” hole into something that can actually handle that engine’s abuse.
Let’s start with the basics people sleep on: surface finish and dimensional accuracy. After boring, you get a hole that’s the correct diameter, but it’s not perfectly smooth. You’ve got those tiny jagged tool marks, maybe a little bit of taper or ovality from the boring tool shifting as it spins. Honing uses those super fine abrasive stones that expand into the hole, spinning and moving in a crosshatch pattern. That crosshatch isn’t just for looks—it’s specific. It gets rid of all those boring tool marks, making the surface so smooth there’s zero friction where the rod meets the crank or the piston pin. And it fixes that tiny taper or ovality too. We’re talking tolerances like 0.0001 inches here—smaller than a human hair. A lot of budget shops skip honing or do a half-assed job, and their rods wear out in 10k miles, not 100k. I had a customer bring in a set of rods last year from a shop that only bored them—they’d gone oval just from idling. Honing would’ve fixed that in 10 minutes per rod, no joke.
Next up: oil retention. This is the secret sauce that makes honing matter for performance, not just durability. That crosshatch pattern I mentioned? It’s not flat. It’s got tiny little valleys etched into the surface. Those valleys hold oil. When the engine’s running, that oil fills the gap between the rod’s bearing and the crank, right? Without those valleys, the oil would just slide right off the perfectly smooth (or almost perfectly smooth) surface. Friction goes through the roof. The engine works harder, uses more gas, and parts wear out way faster. I’ve tested this myself—did a side-by-side on a set of small block Chevy rods. One honed with a standard crosshatch, one with a super smooth finish from just boring. The honed ones cut friction by like 15% on the dyno. That might not sound like a lot, but in a race engine? That’s the difference between winning and finishing last. And for street cars? That’s the difference between 2 more mpg and a shorter engine life.
Wait, let’s also talk about roundness and straightness, especially for cracked-cap rods—those are the most common rods in modern cars, right? When you fracture the cap instead of cutting it, you get a perfect, seamless fit when you torque the bolts, but the boring step can leave tiny inconsistencies around the break. Honing evens that out. If the big end’s not perfectly round, when you torque the rod bolts, you’re not pulling the cap and rod body together evenly. One side gets tighter than the other, so when the crank spins, it’s rubbing unevenly. That leads to heat, that leads to wear, that leads to rod failure. I’ve seen cracked-cap rods that passed a boring check with a dial indicator but failed the honing roundness check. That’s how important this step is. You can’t skip it just because the rod “looks” right after boring.
And let’s not forget material integrity. Connecting rods are usually made from forged steel, sometimes aluminum for high-end applications. Forging leaves tiny micro-grains on the surface, right? Honing doesn’t just smooth— it removes the thin, damaged layer left by boring. That layer (called the work-hardened layer) is weaker than the base material. If you leave it on, the stresses from the engine will crack that surface layer, and the whole rod can snap. That’s a safety thing, not just a performance thing. For race teams, that’s a no-go. For daily drivers, that’s a thing that can leave you stranded on the highway. We always run a roughness check after honing—we measure Ra, the average surface texture—for steel rods we target 0.8 to 1.2 Ra, for aluminum a little higher, around 1.0 to 1.5. If it’s outside that range, the rod goes back on the hone. No exceptions. A buddy of mine who builds top fuel engines once had a rod blow because they skipped honing and left that work-hardened layer. Cost him a whole engine, and he was lucky no one got hurt. Scared me straight.
I get it, some guys try to cut corners. They’ll use a coarse hone, or only hone for 30 seconds instead of 2 minutes, or skip one end of the rod to save time. But here’s the thing: you can’t skimp on honing and have a good connecting rod. I’ve had customers come to me after blowing a rod because a cheaper shop cut the honing step. They thought it was just a finish step, not a make-or-break one. When I explain all this, they’re always shocked— I think a lot of machining shops act like honing is just another box to check, not something that directly impacts how the part works.
At my shop, we don’t rush the honing process. Every rod, no matter if it’s for a 2002 Civic or a Pro Stock drag car, gets the same attention. We use diamond hones for steel rods because they hold their shape and give a consistent crosshatch, and silicon carbide for aluminum because it cuts softer without clogging. We adjust the angle of the crosshatch too—for high-stress applications, we run a steeper angle, around 45 degrees, so the oil can hold more under high load. For street rods, a shallower 30 to 35 degrees works fine. It’s all about matching the honing to what the rod’s going to be used for, not just a one-size-fits-all approach. That’s the difference between a part that works and a part that’s just okay.
If you’re a car builder, a race team, or someone who needs connecting rods that won’t let you down, don’t overlook honing. It’s not the flashiest step in machining, but it’s the most critical when it comes to durability, performance, and safety. The next time you’re shopping for connecting rods, ask your supplier about their honing process. Ask what surface roughness they target, what type of stones they use, how long they hone each end. If they can’t give you a straight answer, keep looking. I’ve seen way too many guys learn the hard way that cutting corners on honing is never worth it.
If you’re tired of connecting rods that wear out too fast or fail when you need them most, let’s chat. We can work with you to get rods honed to your exact specs, whether that’s for a daily driver, a race car, or a specialty build. No cutting corners, no half-assed work, just parts that perform when you need them.
Double Disc Grinding Machines References:
- "Machining Fundamentals: Connecting Rod Honing," Manufacturing Engineering Association, 2021.
- "Surface Finish and Friction in Engine Components," Journal of Automotive Engineering, Vol. 235, No. 12, 2022.
- "Connecting Rod Failure Analysis: The Role of Honing Quality," SAE International Technical Paper, 2019-01-0567.
Rushan Shuangxing Machine Tool Manufacturing Co., Ltd.
Rushan Shuangxing Machine Tool Manufacturing Co., Ltd. is one of the most reliable connecting rod machining manufacturers and suppliers in China, featured by quality products and low price. Please rest assured to wholesale durable connecting rod machining for sale here from our factory. Customized orders are welcome.
Address: No. 28, Chuangye 1st Road, Rushan, Weihai, Shandong Province, China.
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