5-Ball Racing 2012: Chapter 10, Bonne Belle

I was told twice to pump up our K-Model side valve compression to 9:1. Didn’t seem like a problem to me, in my flathead ignorant bliss. I spoke to Lee Chapin, the master of Mikuni carburetors for several decades. “The 9:1 compression will work well with a 42mm Mikuni,” Lee said.

I rode over to the Branch O’Keefe headquarters, where the masterminds of headwork reside. They agreed with the 9:1 level, but then I spoke to flathead gurus and another performance story unfolded. When it comes to racing wrench heads from all over the world will reach into any pocket, on any corner of the earth for help. I stumbled into Maggy Valley, North Carolina, and the Wheels Through Time Museum. During a harried tour of the motorcycle-god-like facility, I sprang the compression ratio question on the master of metal mayhem, history, performance, secrets, you name it. Dale Walksler is as close to a Harley God as a man can become. If you have a bucket list, the Wheels Through Time Museum, must reside at the very top.

Dale looked at me as if I was nuts, when I suggested the elevated compression ratio. In fact, he helped us locate many of the K-model components for the Bonne Belle. “I only have one flathead that contains that level of compression,” Dale said, “and it runs like shit, and must be advanced to dangerous levels.” I spoke to Duncan Keller, a magnum engine builder who mirrored Dale’s sentiment. I immediately called Lee Clemens, “Belay my last,” I said while my cell-phone signal scratched and blurred along a Shady Valley winding road.

Lee was relieved. Here’s the deal with side valve flatheads. The valves are not over the piston, so the combustion area must arm wrestle between the ports, the piston, and the sparkplug. Consequently, if the compression is enhanced, the combustion area is basically squished preventing the air fuel mixture from rolling over to the piston, where the spark plug resides directly above the piston. It could actually fire above the valves and push the piston to the side, instead of down. At least that’s my understanding.

The engine could face final assembly, at last. Lee also required Dale’s assistance with the intake manifold. He chose to modify a stock K-model intake Y-manifold and add a Mikuni friendly spigot. I may need to build an air-box when the engine arrives. We want to keep the Mikuni components in tight to the engine for the aerodynamic equation.

In the meantime, the Bonne Belle powder coating returned from Tony Pisano’s shop. Two new tires arrived from Avon and we ran them over to Settle’s Cycles for mounting and balancing. We scrambled into the shop and started final assembly with the front end first.

I also had a couple of conversations with Aaron, at D&D exhaust regarding pipe design, which reminds me. We are looking into how a pipe attaches to the head exhaust port.

I hauled ass up to Baker’s Performance for fittings, and mounted the Kustom’s Inc. Oil tank. I bite my nails as I stumble into final assembly. I’ve never built a motorcycle without all the components at hand. It’s going to be interesting when the engine arrives and we attempt to line up the BDL primary after significant guesswork. Let’s see what happens next.