® A Day in the Life: Little Shavers

I learned about valve recession the hard way. All engines have to a greater or lessor degreee a tendancy toward valve recession. It's the main way valves wear. However, during the early 1980s Kawasaki had a rash of Ninja bikes failing their exhaust valves due to just incredibly swift valve recession. And the problem is, receeded valves don't always show on either a cylinder compression or leakdown test. Perhaps the machine that taught me this lesson was a Ninja 250 that just would not behave. In for poor idling, I adjusted this bike's valves, checked fuel flow, cleaned its carburetor jets, and checked compression, and when faced with no improvement for all this work, had done a leakdown test on top of it all, and still could not come up with the reason for its erratic idling. The bike had a California evap system too, and for a while I wondered if that was the problem. Charcoal canisters exhibit their own brand of deliquency. However, what the problem ended up being was, after repeating the leakdown test multiple times and rotating the crankshaft each time to a new TDC, I found the leakdown varied randomly with different stops at TDC compression! Huh!? Yup. Pulled the head and sure enough, the exhaust valves were badly receeded, you could of shaved with them they were so sharp-edged! But amazingly, they still sealed most of the time. Just not well enough at 1100 rpm to result in a stable idle. After that I was on the lookout for this problem, and I saw it in all sorts of engines, big and small. Some slight, some severe. But all were little shavers.

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