Tune an Engine

The art of engine tuning is a science many fine authors have spent hundreds of pages trying explain. Honestly, it’s not that complicated. Here’s how to tickle another paddock of ponies out of a four stroke

Ray Stringer’s been around race bikes his entire life. Having won races as a privateer in British Superbikes and beaten the likes of Freddie Spencer, Carl Fogarty and Ron Haslam on self-financed, self-built bikes, Ray went on to run the Kawasaki British Superbike team, the Level 3 Yamaha squad as well as building engines for various teams on a wide range of machinery, from Aprilias to Yamahas.

There’s not much Ray doesn’t know about the four-stroke cycle and how to improve its performance. Here’s his easy, step-by-step guide. Get the tea on, whip your motor out and stand by. Thanks to Ray on (01455 213366.

1. Check it out

The first thing any reputable tuner will do is give the motor a thorough check over. “I always like to take as many measurements as I can to get a real feel for a motor,” says Ray. “For example, measuring the valve clearances and checking the shim sizes gives me an indication of the consistency of the valve seat machining. Going right through the motor before it comes apart is absolutely vital to work out how I can improve it and which parts need replacing or upgrading to prevent engine failure. A good engine tune is generally a safe tune.”

Other measurements include piston-to-valve clearances at various crankshaft positions either side of top dead centre (TDC), which are measured to give Ray the data he needs to prevent any potentially terminal meeting of valves and pistons, either through either excessive skimming of the head or excessively wild cam timing.

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The strip and clean

2. The strip and clean

The next thing a tuner needs to do is to strip and clean the components thoroughly. In fact, cleanliness is a major part of working on a motor. Swarf and debris doesn’t sit happily in a machine with so many moving parts, built to such tight tolerances. 90% of tuning involves work on the cylinder head, so first the camshafts and valves need to be removed, shortly followed by the springs, shims and collets.

Everything is laid out in order of removal before being cleaned meticulously. The cylinder head is then thoroughly washed off in readiness for the next stage of the process. This will usually be skimming some material off the cylinder head face before any porting work is carried out. Skimming trues up the face of head while also marginally increasing the compression ratio, boosting power. Skimming requires specialist machinery. And no, that doesn’t mean a Dremel.

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Skimming and flowing

3. Skimming and flowing

Taking material off the cylinder head’s mating face or using a thinner cylinder head gasket will achieve an increase in compression (the amount of force required to compress the fuel/air mixture in the combustion chamber before it’s ignited). There are many factors to be taken into account to get this right, piston-to-valve clearance being just one.

Porting (or gas flowing) is about getting the fuel/ air mixture into the combustion chamber(s) and the exhaust gases out more quickly. More gas flow means more power. Typically a tuner will try to open up and straighten the ports as much as possible, giving the gases a less convoluted path to aid flow. Shape and volume are also critical so tuners often fill in certain areas of the port with liquid metal, often known as “bog”. Standard engines may also benefit from simple port cleaning – the removal of machining marks left by mass production.

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Rebuilding the motor

4. Rebuilding the motor

Once all the engineering work has been done and the tuner is happy each port has been machined and measured identically, and that the head has been skimmed correctly, reassembly can begin. If the camshafts have been changed, there’s a good chance that the tuner will want to alter the timing to suit.

With the cylinder head rebuilt, it can then be bolted back onto the block. Tightened down in a sequence to a specific torque setting, the crankshaft position must then be “timed up” to the camshafts using dial gauges. These accurately tell the tuner the position of the pistons in relation to the valves, allowing him to keep the piston-to-valve clearance safe as well as being able to alter the character of the motor through different cam timing. Much of this depends on the customer’s budget and how he wants his engine tuned – different states of tune give power in different parts of the rev-range.

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Final checks

5. Final checks

Once the motor has been assembled and the cam timing calculated and marked, the tuner will then check and adjust the valve clearances. This is known as “shimming up” – changing the shims that sit underneath the cam followers to adjust the clearance between the cam lobes and the followers.

With the engine bolted back into the bike, oil is added, the cooling system is topped up and every connection is checked before the engine is turned over to get the oil round. As the engine will be dry, care is needed to ensure oil has reached all the vital oilways before it’s revved. Once the engine has been warmed and cooled, the next stage will be the dyno. With a new state of tune, the motor will need more fuel. This is where a race kit ECU or a Power Commander come in handy since they’re adjustable to give the bike the amount of fuel it needs to match the improved gas flow of the engine. Job done.