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Going Full Bore

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Written by Randy Fox   
Saturday, 03 November 2007

My Parts Selection

Cylinder sleeves, Yamaha Road Star

Everyone has their own tastes and goals for a project like this. You'll have to make your own choices. Each choice you make will affect the complexity of your project and the final outcome of your bike. My choices resulted in a rather high project complexity, so you may be able to skip some of my steps if you make different choices. Here's what I liked about the parts I chose:

  • The Nemesis 102mm diameter, (113ci) pistons are only 17 grams heavier than stock. The more your new piston weight varies from stock weight, the more vibration the engine will produce. To counteract this, well equipped machine shops will be able to re-balance your crank, if you're willing to split your crankcases to remove it. Also, please see the Supplier Selection section at the end of this article.

I did not have my crank re-balanced. It would have cost an additional $100 or more, and (according to Nemesis) the re-balancing would have been minor because of the tiny weight increase.

  • Nemesis Racing valve springs are just slightly stiffer than stock, but offer the longest travel of any aftermarket springs, to help prevent valve float at high RPM. I like that idea. I mean, ideally, you want to use as little of the engine's power as possible to push valves down. Unduly stiff springs consume power and wear valve-seats.
  • Nemesis coils and Nemesis sparkplug wires. Here's what Joel (Odo) Parker (Road Star Clinic author, and professional Yamaha mechanic) has to say:

“… Our coils are rated at 1.53 ~ 2.07 ohm resistance, (99 to 03's), so, getting that rating right in there with how our systems work, is essential.
The Dyna coils for our R*'s are 2.2 Ohms, (A little too high). The Nemesis coils are 1.5, ('JUUUSSSTTT' right). More spark for the system.”

  • The Mikuni HSR42 flat-side carburetor has worked out so well, I could kick myself for not installing it sooner. The throttle feels so much more predictable. It's a major upgrade experience, with a minor installation difficulty. However, not all Mikuni HSR42 carbs are the same. Some are sold with brackets for using stock throttle cables--others are not. Some are sold for use with a fuel pump--others are sold for use with out. Some suppliers will pre-tune the carb for your bike's setup--others will not. You must decide all these issues, in addition to price. I got mine from Bulldogscustomcycle.com.

Note: Do not try using your stock carb with a big bore engine. As I understand, trying to get it to work well is a nightmare, and it severely limits the engine's power potential.

  • 4-Gauge starter cables, or other larger gauge wires, are nearly a necessity for a big bore engine. See the Installing Bulldogs Starter Cables and a Warrior Starter article in this website for more information.
  • The Barnett clutch kit consists primarily of a replacement pressure-plate and springs. The rest of the stock clutch setup is purported to handle the greater power of a big bore without difficulty. The stock pressure plate, however, just won't handle the power of a properly built big bore engine. See the How to Install the Barnett Clutch With New Oil Pump Gear in this website for more details.

Some have had success with using the pressure plate set-up from the Road Star Warrior. I chose to go with the Barnett to be sure.

  • A Warrior starter is not absolutely necessary, as I understand, but I installed one just the same. It has about 35% extra power over the stock one. I didn't want to tempt the motorcycle gremlins, and get stuck somewhere with a burned-out or feeble starter. See the Installing Bulldogs Starter Cables and a Warrior Starter article in this website for more information. I got a chrome one from www.sxygramps.com.
  • There are 4 choices in pushrods: Stock, Adjustable aluminum, Adjustable titanium, Custom made fixed length.

I learned that adjustable pushrods for Road Stars, regardless of where you buy them or who’s name is logo-ed on them, are manufactured by Smith Brothers. Therefore all I had to do was compare prices. I went with Nemesis Racing aluminum pushrods.
Lighter pushrods mean less energy is wasted inside the engine--pushing them up. I could have saved a little more weight by going with titanium, but it would have been three times the cost. I just didn't feel that the microscopic horsepower increase justified the high price jump.
Pushrod adjustability allows you to take most of the top-end chatter out of the engine. See the Assembling the Top End document in this article series for details.

  • Several aftermarket lifters are reported to be exactly the same as OEM, but cheaper. I used Sealed Power HT-2011, available from many auto parts stores.

Note: If you replace your cams, you must replace your lifters, according to Nemesis Racing, Crane Cams, and other sources.
 
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