...Or, how not to break down...Our Service Department does a lot of performance work on bikes. We do everything from pipes and hi-flow to full blown 120 kits. It is sometimes routine for us, but almost never for our customers. It is sometimes hard to explain that one should not just look at the engine on their bike for performance enhancements, but look at the whole bike. You could pick out the very best cam, the very best cylinders and heads that the aftermarket has to offer. Then mate it to the very best exhaust system and electronics to fire the whole thing up, but if the parts are not tested together the whole job is nothing more than a crap shoot. Sometimes you win, but most time you will crap-out. It is also important to understand just how the parts that actually put the increased power to the ground like the primary drive, the secondary drive, as well as the wheel and belt pulley, react to performance work. It is quit a journey, and you may be surprised.
Let me tell a tale of what happened to one of my projects several years ago. I purchased a wrecked 1997 Classic from a local salvage yard. The bike was structurally sound, but with a lot of sheet metal damage. My plan was to attach a stock Harley sidecar to this bike. Knowing that with all that additional drag on the bike I decided it was time to put some serious horsepower to the ground, and thought this would be the perfect platform for my project. I sourced a 120ci Screamin’ Eagle twin cam engine and with some very minor upgrades to the stock swing arm it fit right in. I decided to go with a twin-cam because of the way it mates with the tranny. Twin-cam engines and transmissions mount together sort of auto style with the transmission bolting right to the engine block with four heavy bolts instead of just relying on the inner primary to hold everything together. I figured that with all this additional power I would need to upgrade some other parts of my project bike so along with the engine I installed a heavy duty compensator sprocket and chain, and a heavy duty clutch. That should take care of the primary.
I was sure that now I would have no trouble getting the power to the tranny. While I was at it I thought that a nice upgrade would be a P&A 6 speed gear set for my new twin-can tranny case. I was not going to make any changes to the size of the rear tire so I retained the early wide belt and sprockets. Those would surely handle the additional power. The engine had a mechanical compression ratio of 11.5 to one. So along with the compression releases in the cylinder heads I was sure I would need a heavy duty battery, a heavy duty starter and starter drive. I also installed a smaller pinion gear on the starter drive and a heavy duty ring gear on the clutch basket. Those modifications also changed the ratio between the starter pinion gear and the ring gear to make it easier for the starter to spin the big inch motor over. The stock FXR engine mounts were also replaced with heaver duty units and would still need to be monitored closely. But now I thought I was done.
A few months later all the sheet metal was back from the painter, all the modes were complete and all that was left was installing the paint and firing up for its maiden voyage. The engine fired right up and off I was for my first ride. Everything was going fine and over the next several weeks I put on about 2000 break-in miles on the bike. Everything checked out fine and now it was time to see what it had. First order of business now that it was broken in was some hi-speed full throttle runs on the dyno. This allowed us to tune the engine, and control the fuel ratio. After it was tuned we did some high speed runs to see just how much power we had. Not too bad, just under 130HP with a torque reading of just over 140lb. Not too shabby. Next were some real world road tests.
Off I went down Route 1, on my way to our other location, and about two miles down the road I was stopped by a light. I thought that this would be the perfect place for a little side-hack burn out. So I thought. I brought the rpm up to about 3800 and dumped the clutch when the light changed, and to my surprise no burn out, no nothing. Thought I blew the clutch or maybe popped a belt, but that is not what happened. Because of the additional weight of the hack and its related parts, the rear wheel caught traction, the primary sprocket turned, the wheel sprocket turned, but the wheel did not. This 140ft lb motor ripped the webbing on the wheel sprocket, sheered the bolts that hold the pulley to the wheel hub, and ripped the wheel hub from the spokes on the stock cast wheel. What a mess. Total cost of the damage not counting my labor to replace the wheel, the wheel sprocket, and the bolts about $1500 bucks. Very expensive lesson.
That is just the reason Harley’s fitment is so precise. Harley’s hi-performance kits come with parts that some think are unnecessary. Our newest kit, the 120ci, comes with a heavy duty clutch and compensator. It is also the reason that it is not recommended on 07 and earlier. The 08 and later bikes come with a rubber cushioned wheel and sprocket that will take up some of the shock load and not tear the wheel and sprocket up so much. When you build a hi-performance motor, depending on how much juice you give it, everything down the drive line needs to be beefed up to take the strain. What you will find is that if you juice up a twin-cam over 100HP, depending on your skill as a rider, you could easily exceed the bike’s design limits.
What I would like my readers to take away from this article is - yeah, lets hop-it-up. Let’s add all the go-juice we have in the bottle, but do your homework. Do some research and don’t blindly believe all the ads in motorcycle magazines. Most are crap at best; some are actually dangerous. Once again, use my people as your resource for information. We here at Liberty and Highroads have a lot of experience with performance work, and also the right equipment. We spend a lot of money sending our technicians to the factory schools to train our people the right way to do things, the Harley way, you may say. The Motor Company also spends a lot of time and money carefully putting together their kits, so the parts work in concert with each other to maintain that very reliable, and still ridable Harley-Davidson.
~Tom
Pick up your copy of the Informer at Liberty H-D or Highroads H-D - and look for the next issue this spring!
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