Top End Refresh: Part Two | Bennett’s Performance Cylinder Honing
Tech In Depth
Freshening up the top end on your motorcycle can drastically improve its lifespan. We have a ’95 Road King with 60,000 miles that needed some TLC.
Last month we took you through part one of this three-part series where we removed the ’95 Road King’s top end, giving the cylinder heads to Branch-O’Keefe to reshape the heads’ combustion chamber, which increases compression, and to port and polish the heads, which flows air more freely and unobtrusively.
This month for part two, we headed to Bennett’s Performance to hone the cylinders in order to accept the new +0.005-inch (five thousandths of an inch over stock) Harley flat-top pistons. The bike’s owner stumbled upon this Harley flat-top piston kit (Teflon-coated cast aluminum pistons, clips, rings, and pins; about $150) in his garage so the JIMS +0.005-inch flat top pistons that were to be used originally weren’t needed.
Normally, cylinder boring (most commonly done on a machine called a boring bar, but can also be performed on a lathe or a mill with the right attachments) needs to happen when using at least +0.010-inch over stock pistons or larger, according to Eric Bennett, owner of Bennett’s Performance. In this case, boring could potentially remove too much material for this project, but when Eric does bore a cylinder, he uses a Kwik-Way automotive-style boring bar with a motorcycle-specific triangle plate attachment to remove thousandths of an inch of material from the cylinder in a matter of minutes. The machine is similar to a drill press in that it’s lowered into the cylinder with titanium nitrite coated cutters to remove the desired amount of material very precisely and accurately. Once the desired amount of material is removed via the boring bar, the honing takes place.
Honing is basically the refining process of the freshly bored cylinder. Since Eric only needed to remove 0.005-inch from the cylinder, honing was only necessary for this application, and since the honing machine removes material while simultaneously creating the necessary crosshatch pattern inside the cylinder walls, it essentially kills two birds with one stone.
The hone is a tool consisting of multiple fine abrasive slips (picture a beater attachment on a cake mixer) that are rotated via a drill to impart a smooth finish inside the cylinder. There are varying coarse hone slips available depending on the application, but in this case, Eric only needed a 280-grit hone. The hone is moved up and down inside the cylinder to create a crosshatch pattern. This is crucial because the crosshatch creates peaks and valleys where the oil gets trapped inside the valleys to lubricate the pistons and piston rings, and the peaks aid in seating the rings to prevent oil consumption and smoking. If you didn’t have a crosshatch pattern you’d burn oil, according to Eric. Bennett’s charges $100 to hone the cylinders. For boring and honing, it costs $200.
Follow along as Eric Bennett demonstrates the step-by-step process of how to properly hone a cylinder. If you missed last month’s installment, log on to hotbikeweb.com for the full article.
(847) 759-0190 | andrewsproducts.com
(562) 498-1819 | bennettsperformanceinc.com
(562) 597-2850 | branchokeefe.com
(800) 752-9850 | cometic.com
(805) 482-6913 | jimsusa.com