Many times over the past few years I have been asked questions such as these, “Where did the idea for the bolt-on big kit for the Harley-Davidson® and Buell® motorcycles come from?” or “Why didn’t the Motor Company do it first?” or perhaps the most relevant in many folks minds “Why do it at all?”. All are good questions and the time has definitely come to put pen to paper, if only metaphorically speaking in the 21st century, and tell the story behind the product.
Early in 1998, the AMA Flattrack Racing sanctioning body was looking for viable, lower cost alternatives to the venerable XR750 to not only increase interest in a somewhat waning sport but to hopefully bring back the brand vs. brand rivalries of the early and mid 1980’s. The Supertracker series was born and initial ground rules were laid out to allow for overhead cam engines which were limited to 1000cc and pushrod engines limited to 1250cc. This immediately opened the door for the XL/Buell based 1200cc engine to step into the arena formerly dominated by purpose built racing platforms. Several teams, including my own, set about designing and testing purpose built racing chassis’ with what had been, heretofore, a pretty benign engine in the Motor Company line. Given that we were allowed the displacement, the first thing we did was take our best set of OEM cylinders and bore them to 3.563" with custom pistons to match. The first season of this series was to start in 1999 so durability testing began in earnest. Initially the boring option appeared to a viable route early on but anomalies began to start popping up once the bikes made it off the dyno and into the world. What we found was that the engines were initially very sound units with initial “green engine” leak down figures in the 1-3% range. Post initial break-in the figures generally stayed in this range even after upwards of 80-100 dyno pulls while cam and cylinder head variables where being sorted out. The real issues began to arise once the bikes got out into the world and varying engine loads and temperature fluctuations became a factor. What happened was that cylinder and ring seal integrity more or less “fell off a cliff”. We would begin testing with a solid engine but generally within 8 miles on a 1 mile circuit or within 20 laps in a half-mile environment the leak downs would skyrocket into the 40-60% range and piston skirts would begin to collapse. Upon inspection of the cylinder/piston combinations we found a myriad of issues, but the biggest by far was that the OEM sleeve was moving in the OEM casting even though the sleeve is a cast in unit rather than pressed. In many instances the decrease in hoop strength of the cast iron sleeve and dramatic thermal dynamic differences between the two materials caused the sleeve to physically separate from the surrounding aluminum. In other, less severe instances the physical lack of support secondary to the rather poor tensile strength of the OEM casting simply could not support the increase in engine load and the aforementioned lack of hoop strength would just cause the bore to warp out of appropriate tolerance range.
Millennium Technologies, LLC was formed in 1997 by Chris, Marnie and Jim Hackl to fill a gap in the United States nickel-silicon-carbide plating industry. Almost from day one the company was involved with Harley-Davidson Motor Co., Gary Stippich (at the time the lead engineer on the XL power train and also the head of the engine department for Buell American Motorcycles factory supported road racing efforts) and Don Tilley of Tilley HD-Buell. Close ties had already been established because of not only the durability of the Hackl’s particular plating techniques but because of the development of the new type alloy used in the Revolution Cylinders (Yes, there were Revolution cylinders long before there was a Revolution Performance) that promoted excellent ring stability and thermal dynamics. I contacted Chris to explore the option and potential viability of producing an alloy cylinder with a plated bore that would live under the circumstances that we wanted to subject it to. Chris was on board immediately and the first bolt-on big bore, all aluminum cylinders for the Harley® was born. Initial product was received and testing began immediately. Initial leak down numbers were extremely acceptable being located in the 1%-3% range immediately following an initial three heat cycle routine. The engine was then subjected to some pretty brutal dynometer testing with AFR readings purposely raised to the 13.7-14.0 range to put as much heat into the cylinder as possible and then re-evaluate its overall integrity. Over 200 pulls were made and the engines were compression and leak tested then disassembled for component evaluation. Post run leak downs remained consistent with no percentages exceeding 5% on any cylinder with testing done at both top dead center as well as bottom dead center. After tear down, cylinder bore circularity was more than acceptable with tolerance variances of less than .0002 with regards to 6 points top to bottom requiring only a ring replacement before rebuild.
On to the track. Testing began in earnest immediately following reassembly and a total of 600+ miles of 7500+ rpm use were logged. Valve train components were changed rigorously to avoid breakage but the cylinder/piston combination was otherwise unchanged. RPM variances down to 3000 rpm followed by a high gear, full throttle application to significantly inertial load the engine were performed in 90+ degree ambient temperatures to push the limits of structural integrity. During this process leak down testing was done every ten laps to gather data to compare directly with the previous incarnation. It was not until approximately 100 miles of essentially full throttle use that leak down figures began to diminish and not until 150 miles did they exceed our 5% ceiling which dictated a ring and piston replacement.
Given the information that we now possessed it was very clear that we had a winner. The TC88 was recently introduced and given our experiences it seemed to be a natural product base for the same technology. The first thing we did was remove and bore a set of Twin Cam® cylinders to dimensionally the same parameters as the XL’s which resulted in the current 98cid configuration. Dynometer testing commenced and we found almost exactly the same results as we did with the XL based engines in the fact that the leak down and compression data stayed consistently acceptable as long as the engine was only dyno tested (even upwards of 150+ runs) and was otherwise ridden normally. As soon as the riding style became more rigorous though or power levels were increased to the 95-100 rwhp range and beyond, the overall integrity of the cylinder would began to degrade and would subsequently reach a threshold and go away completely. This was generally after 2500-3000 miles but could take as long as 5000 miles. Leak downs would climb slowly just as they had in the smaller displacements and then suddenly skyrocket to the 40%-60% range. Upon disassembly we discovered that, just as before, even though the liner was cast in, the hoop strength was significantly diminished because of the varying thickness not only in the areas of the cylinder studs but by the overall design and material of the sleeve and casting in general. The overall thermal dynamic differences of the two materials were too much for the cast in adhesion to overcome and the marriage failed. Miserably. Again, best case scenario was that the cylinder would simply warp so far out of round that the rings could not overcome it. Worst case is that the sleeve/casting adhesion would fail due to the warping and the sleeve would physically separate from the surrounding cast and begin to cock and sometimes even turn in the bore. The latter scenario caused all kinds of unpleasant consequences.
All these facts beg the question as to why, if this is so great, doesn’t the Motor Company use this type of product as a base material in their OEM machines? The answer comes in the form of cost and the platform that is the OEM Harley-Davidson V-Twin. Harley-Davidson dictates that at least 75% of their bill of materials must be manufactured in the United States with the bulk of the 75% to include the chassis and power train. With that said, these type cylinders are significantly more expensive to produce here in the states with only four major players in the country with enough knowledge base to mass produce a plated bore cylinder. The other reason is probably that they do not seem to have an issue selling the bikes the way they are. Why change? The fact of the matter is that the motor company is the last major manufacturer on the planet not to embrace this type of technology. As I have stated many times before, all other major manufacturers currently use all aluminum cylinders with plated bores in not only their water cooled over square engines but in their air cooled under square engines as well. All Yamaha Star® cruisers, Victory® cruisers and so on have already implemented this technology with great success. This pretty well squashes the notion that this type of product is only relegated to high revving, over square, water cooled engines. It is also of note that at least two of the major aftermarket aluminum automotive block companies have recently switched from iron sleeved aluminum blocks to all aluminum plated bore. These engines incorporate up to 5.0" of stroke with bores as large as 4.750" in diameter. Is this technology for use with all applications? Not at all. There are certain disciplines of racing that an all aluminum platform cannot support. Extremely high cylinder pressure situations such as nitromethane (which nickel-silicon-carbide hates by the way), high level nitrous, or extremely high levels of forced induction can wreak havoc on them. We know this for two reasons, one, we aren’t naive and two because we are involved with such teams as Ganassi Cart and have seen what 60+ pounds of boost can do to the bores. This is the realm that, currently, only cast iron of the highest quality will survive in. Reality is that 99% of people don’t operate in this environment with their street machines and this is our primary customer base focus.
I realize that I have probably only scratched the surface of questions surrounding our product and I do intend to keeping posting these hopefully informative articles as I have time. Until then we will continue to test. Continue to innovate. Continue to improve. And continue to educate. Thank you so much for taking time to read this little epistle and hopefully it helps you, the consumer, to make appropriate decisions regarding how you purchase for the project that is not only your passion but ours as well.
Brian Nallin and Chris Hackl
Owners of Revolution Performance, LLC and Millennium Technologies, LLC