How They Work K-series tensioners aren't terribly complex and, simply put, do little more than push a small piston back and forth against the engine's timing chain guide, keeping the chain tight. They do so hydraulically-not unlike older H22A tensioners-which means K-series tensioners operate by way of oil pressure, but they also incorporate a small, internal spring for mechanical purposes. At low engine speeds, when oil pressure is low, the tensioner's internal spring mechanically moves its piston toward the timing chain guide, reducing chain slack on the chain's exhaust side. As engine speed and oil pressure rise, the spring relaxes and oil pressurizes the tensioner's chamber, hydraulically pushing its piston toward the chain's guide. A check valve ensures the oil doesn't escape prematurely and a release valve lets it out when the tensioner's done, well, tensioning things. Additionally, a ratcheting mechanism and teeth built into the piston ensure that it doesn't retract too far back into its housing and loosen up the chain. Sounds like Honda has it all figured out.The Problem Unfortunately, Honda's internal tensioner spring doesn't always work as you'd expect, and excess tensioner piston travel (more than 0.25-inch) and timing chain slack when oil pressure is low is common-especially while cranking and at low engine speeds when the spring is doing all the work. The results can cause the piston teeth to slam against the tensioner's ratchet, ultimately grinding their tips off, rendering them ineffective. You see, by design, K-series exhaust valves close rapidly. Each time they slam shut, the chain builds slack. And each time they slam shut, the tensioner's piston bashes against its ratcheting mechanism. Aftermarket cams with aggressive profiles and stiffer valve springs only pronounce this. It should be noted that although dealership technicians have reported worn tensioner pistons on otherwise stock engines, it's more likely once camshafts and springs have been swapped. Steeper exhaust closing ramps and stiffer valve springs that close the valves even quicker are to blame. Of course, none of this is good since the ratchet and piston teeth are the only things that prevent the piston from being pushed in too far. All of this can lead to a loose chain, a failed safety mechanism, and engine damage, even on unmodified engines. Worst of all, you'll never know any of this is happening until it's too late since you can't readily monitor the tensioner and, even if you could, all of this happens way to quickly.
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