Engine Rebuild and Tuning

Horsepower is an addictive thing. And while not a replacement for sheer riding ability, it will at some point in your riding career play a role in both going faster and having more fun at the racetrack. How do you go about getting more of it, assuming you've already made the more straightforward modifications like an exhaust system, fuel controller, and/or re-flashed ECU?

For anyone who wants to take his trackday riding or racing to the next level, the answer is an engine build. Of course, that's a broad answer, as the term 'engine build' can mean any number of things depending on who you talk to and what you as the rider want/need. Adding to the complexity of the situation is that, in most supersport-based builds, emphasis is not only placed on power gains but in assuring continued reliability. The reason for this is that, in racing (or even trackday riding), the internal parts turning fuel into power are put under great stress, and over time those components can wear down, so much that a refresh is necessary, regardless of how good the manufacturer's production pieces are.

We've reached out to a professional motorcycle tuner, who illustrates the important aspects of an engine build and removes some of the confusion surrounding the subject.
Note that the objective with this is not to make it so that you can pop into your garage and rebuild your own engine but rather have a better idea of why it's important to go through your engine, what the more important changes are, and how those changes alter your engine's performance. The end goal being that, when the time comes, you can go to your tuner of choice with a better understanding of what you want and need and start the process of getting more of those things you crave: horsepower and assurance.

Second note also that every engine builder will have a slightly different opinion on what works and what doesn't, and your tuner of choice can take a slightly different approach in his quest for more power. All the same, every engine builder will have secrets that he'll remain tight-lipped about and will likely not open up to you about.

You, much the opposite, need to be forthcoming with information when you sit down with a tuner, being sure to clarify which fuel you plan to run and what kind of maintenance schedule you want for the engine. More that that, you'll want to talk about realistic goals for horsepower numbers, bearing in mind what you want to spend on the build and what rules you plan to abide by. Most supersport class rules, for example, prohibit things like cylinder head porting, aftermarket pistons, and other modifications that would provide a more significant bump in performance.

Then again, peak power is not the primary goal with a standard engine build, our tuner remind us, ultimately pointing out that modern sportbikes are already pretty well sorted. 'You know, for something like an Yamaha YZF-R1, you can do some cylinder head work and degree the cams and make good power. But with 600s it gets more difficult because they're already pretty tuned up from the factory. The cylinder heads are pretty good – not perfect – but they're pretty well designed, and so you're just making these tweaks to get the power you want here or there and just checking all of the original equipment parts, replacing anything that is worn and could cause damage down the road.'

Tearing the engine down and inspecting its internals will give you a better idea of what exactly needs to be replaced and what can be reused, with any surprises likely upping the cost of the rebuild. 'If it's – generally speaking – a decent-running engine, it's a good bet that you're not going to have to spend a bunch of money on hard parts like rods, a crankshaft, or clutch basket,' according to our specialist. 'But you do need to tear the engine down to the crankshaft and inspect absolutely everything so that you have a better idea of what needs to be replaced or can be reused.

The big thing to check is that the cylinder bores are round. Because if the cylinder bores are hourglass-shaped or worn, then when the piston comes up to top dead center it can have excessive rock-over, which if it's got excessive rock and you run a tight combustion chamber squish number, that could be a problem since the piston comes up and will do this wiggle thing. If it's worn, the cylinders will need to be re-plated with Nikasil and honed, most modern engines have some form of cylinder plating rather than liners. The pistons need to be inspected too to make sure that the skirts haven't collapsed. And really, with all of this you're just making sure that you're starting with a good core, that everything is in good shape.

Of course, if you end up reusing the pistons, you want to clean up any excessive carbon buildup, like above the top ring land; that way the combustion gases can get down and get the rings pressurized. If the cylinder bores are good, you'll still want to re-hone them – not to remove material but to put a crosshatch into it. That gives you good ring seal. The big-end rod bores need to be inspected to make sure they're round, and the pin bores need to be inspected on the connecting rods, even though on most decent, low-used engines that stuff is generally fine.

After a thorough inspection of all parts, it's time to go about making the changes that will garner added power. Our tuner, who learned much of his tricks from the Yoshimura Suzuki squad, this means performing a valve job, or in other words, making cuts to the valve seat that will change where the valves sit when they're closed. Done via seat cutters, this will ultimately enhance airflow and valve seal.

There are some specific numbers for the angles, and these numbers are going to vary from engine builder to engine builder, but the idea of the valve job is to – done properly, with the proper angles worked out on a flow bench – enhance the airflow and even possibly start the airflow earlier. Really, a lot of the power you make is going to be in the valve job.

Of course in the end you're doing multiple things. Part of it is you're getting the valve to seal the combustion chamber off during the combustion process. You want to contain the gases in the combustion chamber so that they can do their job, and that comes down to ring seal but also good valve seal. At the same time, you're trying to get better airflow. So with a good valve job, you can induce airflow more quickly as the valve comes off the seat. As an example, if the valve has to be twenty-thousandths off the seat before the air starts flowing, then you're giving up that initial half-millimeter of lift. And if you start behind, you're always going to be behind. Do it right though and you can increase power across the board.

Important to note is that for most riders, it's important to not be too aggressive with valve seat angles, as in the end this could affect reliability. And you try to take as little material off as you can because the more valve jobs you do, the more you can sink the valve into the head and give up compression. So you really want to make the cuts in the valve seat as small as possible, and be careful to not sit there and grind and grind on the seat because eventually you'll have to replace the seats or scrap the cylinder head. But for reliability, as long as you don't run a really narrow margin, you're going to be totally fine.Tag: Tuner Tuning Engine-Rebuild Performance Horsepower Torque Exhaust-System Camshaft Mechanical Development Power Maintenance
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