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Auto Repair: Fundamentals Of Electronic Ignition Systems - 1 of 2

More info: www.metacog.com This video is from the early 1990's. It provides rock solid info on electronic ignition systems. It's a great ...

Ignition - Start Toyota Celica 2000 GT Turbo

Ignition Sequence...

Toyota Mark II JZX90 M/T with 2JZ-GTE block (1, ...

Toyota Mark II JZX90 M/T with 2JZ-GTE block (1,5JZ) Pro-Start ignition controller check )

Things you need to know about 4-strokes

VALVE TRAINS Part 1

By Eric Gorr

Modern four-stroke dirt bike engines have a strong lineage in F-1 and Indy car racing. Yamaha’s partnership with Toyota and Honda’s collaboration with Mugen has given us some incredible dirt bike engines. The average 250cc four-stroke revs to 13,400 rpm. At that rpm the piston is moving up and down in the cylinder at 223 times per second, that’s 111 valve events per second. Multi cylinder F-1 and Indy car engines are toast after a 2-hour race, so why do dirt riders expect their four-stroke singles to last for years without maintenance? The answer for most riders is the fear of dealing with complicated valve train systems. Modern valve trains wear at about the same rate as the piston and rings. Some models have characteristic problems that require specialized repairs. Here is a guide to how valve trains work, how to know when something is awry, and some choices on how to fix up your four-stroke dirt bike.

WHAT’S IN A VALVE TRAIN?

A valve train consists of all the parts that work together to control the phases of a four-stroke engine, intake, compression, power, and exhaust. The valve train consists of a cam chain, cam and crank sprockets, cam chain tensioner, cam chain guides, camshaft, tappets or rocker arms, valves, valve springs, valve seats, and valve guides.

The crankshaft drives a sprocket with a cam chain that runs on plastic guides and backed by a tensioner mechanism. The cam sprockets spinning at half the speed of the crankshaft are fastened to the cam with bolts or by interference press-fit. The camshaft lobes ride against rocker arms or tappets that look like buckets and contain a shim-pad to adjust the valve lash. At the heart of the cylinder head is the valve assembly that includes a valve sealing against a seat that is cast into the head and machined to a series of precise angles to maximize flow. The valve is loaded by pressure from a spring, and sandwiched by a base and a top keeper, and held together by a set of retainers. The valve slides through a tightly fitted valve guide with an oil seal to reduce the leakage into the ports.

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