EL Bonnie

Some of fellows from over Wisconsin way have been scheming for several years to put a 1939 61" (model EL) Knucklehead on the great salt flats of Utah - better known as Bonneville. Joe Taylor, the owner of the "project," is joined by Tom Anderson and John Endrizzi in the quest to take home a record in the 1000MPSVG class at the AMA sanctioned annual BUB Motorcycle Speed Trials. For those of you not quite up to speed on class designations (I fit in that category too) the 1000 refers to the maximum displacement in cubic centimeters - hence a 61 inch Knuckle = 1000cc. The MPS narrows it down further, to a frame that is Modified/Partial Streamlining. The final piece of the puzzle is the VG which stand for Vintage Gas, limiting the engine to a production date of 1955 or earlier.

The trio does not walk into this endeavor with no prior knowledge of what they are getting in to; Joe and Tom have previous Bonneville experience racing under the Buell Brothers banner. This build will, however, be their first foray into the vintage side of land speed racing.

As may be expected, a project like this is not without its setbacks. Too small budgets are almost always an issue when regular guys take something like this on. A major setback in this particular build was the untimely death of the engine builder. That will definitely put a damper on a project!

Knowing the predicament that the Buell Brothers found themselves in, I had to weigh my morbidly obese workload against the possibility of being involved in a record setting endeavor. In the end, the deciding factor was this: given my penchant for high performance and knuckleheads, how would I feel if EL Bonnie set a record, but another engine builder's name was associated with it? What could I do but offer my service to build the engine?

Before going any further, it is important to note that a project such as EL Bonnie would be virtually impossible to complete without the existence of a company such as S&S Cycle. S&S has made the commitment to reproduce quality engine parts for these early motors. Witness the parts in the shot below; all from S&S, and all vital to transforming this dream into a reality.

As soon as Joe dropped off the engine, it became apparent that they committed no sacrilege by turning it into a racer. Nearly every square inch of the '39 cases showed evidence of welding repairs. If they could talk, these cases would probably have quite a story to tell. With Joe's permission, I decided it would be worthwhile to do some reinforcement modifications. I added a gusset to the left side of the left front motor mount (which showed evidence of at least one previous repair). Early Knuckle cases are also known to be weak on the left side in the cylinder spigot area. My solution was to weld 3/8" plate to that area, windowed just enough to leave the serial number pad intact.

Moving on to the the inside of the cases, windage is always a concern - at least to my mind. The "pocket" in the right side case quite obviously performs no function other than to save a bit of aluminum during the casting process, and I have always pondered what to do with it. What, if any, effect on windage this pocket has is any one's guess. On the other hand, when it comes to racing, I am a firm believer that the difference can often come down to a matter of adding together all the details. I've heard it before: "Do you really think that will make a difference?" My answer is usually, "We'll see." But the more honest answer is no ....but hopefully when it is added to the other dozen things that are too small to make a difference by themselves, it will!

A couple of thin aluminum plates cut to fit and welded into place smooth out the interior of the right case half. The next step toward minimizing windage was to polish the interior of the cases, including the gearcase. One of the final steps before final assembly on the case will be to treat them with TLTD, a oil shedding thermal dispersant coating.

Now you see it ...

Now you don't

So, if all the previous repairs had not distorted the cases, it was a good bet that with the welding I did, there was reason for concern! Besides, one of the keys to making this motor fast will be to keep the friction losses as low as possible. The first step to ensuring that was to mount the left case to the mill and indicate in the pinion shaft race hole (races removed). Once the indicator showed that it was centered in the hole, I gently installed the right case, torquing all the case bolts. Taking a reading from the indicator in the right side case race hole, I was far from shocked to find .012" runout. A +.025 race in the right case was the cure.

Next, with the cases still bolted together, I decked the bottoms of the motor mounts enough to insure they are true, and then did the same with the cylinder mounting surfaces. Before giving the mill the rest of the day off, I also machined the breather gear bore for the +.030 S&S gear, removing 70 years worth of damage in the process. Installation of the new crankcase races, and line lapping them to size pretty well brings us up to the present. Next is a mock up to blueprint the breather opening in the case and see what kind of piston deck height we are dealing with. To be continued ...