After completing the Quarter Scale Merlin, I took several months off to work on a number of projects that had piled up around the home and shop. High on my to-do list was assembling a number of backup XP computers while the parts were still readily available. I've had an ongoing concern that my ten year old homemade shop computers as well as those running my wife's embroidery machines have been living on borrowed time. I could, if necessary, convert my Tormach to Linux-based PathPilot, but the hardware associated with my Wabeco lathe is still tied to Mach3. I also built up a couple Windows 7 machines so I could have at least one foot inside the modern world. I tried migrating to Windows 7 entirely, but I wasn't able to get some of my ancient CAD/CAM software nor my wife's embroidery software running on their 64-bit operating systems even in their so-called compatibility mode. Replacing all that software was pretty much off the table for me.
Committing to a new long term engine project involved a lot of procrastination and eventually came down to a decision between Ron Colonna's 270 Offy and Draw-Tech's Knucklehead. In order to shake the bugs out of the new shop computers, I modeled the Offy's crankcase as well as the Knucklehead's cylinder head assemblies in SolidWorks. I felt the Offy would probably be of wider interest to others since I'm not aware of any detailed published builds for it. In the end though I felt like I needed more time to consider some alternate approaches to the Offy's one-piece crankcase, and so for now I chose the Knucklehead.
I really liked the looks of Draw-Tech's CAD rendered Knucklehead but wasn't even aware of its existence until I came across Steve (Driller1432)'s HMEM thread:
His successful build validated the plan set and proved the model could be made to run using the original Harley timing. So I decided to do a thread on its build and, along the way, fill in some of the machining steps that Steve left out to perhaps encourage others to build one of their own. There was so much effort put into that engine's drawings that it seems a shame to allow them to languish on the forum's download site.
Even though it has only two cylinders, this engine isn't a beginner's project, though. It's considerably more complex than a Hoglet or even Jerry Howell's V-twin, but the finished result will be more reminiscent of an actual full-size engine.
I decided to begin the build by machining the exterior components of the head assemblies which I had already modeled. This included the heads, cam brackets, valve boxes, and rocker arm boxes. At first glance, the head assemblies appear to be the most complex parts of the engine, and their individual parts must fit precisely together.
My first step was to get hard copies of the pertinent downloaded pdfs since I've never been comfortable with working directly from drawings on a computer screen.
Because some of the key drawings were intended for E-size sheets, I dropped a flash drive off at our local copier store so they could print them out for me on their huge cut sheet printer while I ran some errands. When I returned, though, I was informed that the store's policy was to not copy or print out copyrighted material. They pointed out the title blocks in the lower right hand corner of the drawings that contained words to the effect that the drawings were not to be reproduced without written consent from the original owner. No amount of common sense reasoning could get me past the clerk I was dealing with. Instead of coming back later when someone a little less literal might be on shift, I printed the large size drawings out in poster board mode on my home printer and then carefully taped them together to create the large sheets.
It'll feel good to be making chips again, but with only two cylinders to deal with this time there won't be as many of them. -Terry