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The valve stem seal

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In the quest to make engines as oil-tight as possible, we often forget the effect of the humble valve stem seal. Tucked away inside the cylinder head well out of sight, this small, upturned cup of a device grips onto the top of the valve guide and seals against the valve stem, enabling the valve to open and close without letting comparatively large quantities of oil get sucked down the clearance between the stem and guide and into the combustion chamber. With such a small component - and...

Bottles and tubes

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In the world of motorcycle racing, in particular it seems, it has been common to find strange appendages on exhaust systems, on everything from single-cylinder motocross machinery to high-speed inline four-cylinder engines. They can take various forms, common types being: 1) Tubes linking certain primary pipes together; the link tubes being much smaller in diameter than the primary pipes they connect2) Larger-volume 'bottles' being used to link adjacent primary pipes together3) Pipes...

Fatigue-resistant threadforms

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When we design a fastener, or select one for use, there are a number of points to consider. Not least among these is whether the fastener will last for the life of the engine, or certainly between planned services. Where a fastener is cyclically loaded, we need to consider the effects of fatigue, and in this regard we need to pay special attention to design features. Where a bespoke engine is concerned, or where we are looking to increase markedly the output of an existing engine, it is...


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The world of Formula One is a special case in the technology of engine lubrication. With formulations closely guarded and reputed to be radically different from those found on the service station forecourt, the philosophy behind them is to generate the minimum amount of friction commensurate with adequate component life. But when at one time engines could be changed between practice and the race, now with only eight engines allowed for the whole season the pendulum has moved away from...

The swirl tank

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The advantages of a good dry-sump system over that of a good wet-sump design in a race engine can be broadly stated as those of installation and oil control. The low-line sump pan in the dry-sump installation enables a significantly lower crankshaft centre line and the ability to control the movement of the oil to avoid 'surge' when accelerating, braking or cornering. Once we have removed the oil from the engine, however, one disadvantage is getting back into a state whereby we can...