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How to Degree a Cam: Considerations for VTEC Mechanisms

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Considerations for VTEC Mechanisms


00:00 - If you're dealing with an engine that uses a switch cam design with dual cam lobes for low RPM and high RPM operation such as Honda's VTEC system for example, this adds one more layer of complexity to the cam degreeing task.
00:14 Since the high lift and duration cam lobe will have the most effect over engine performance, it's this lobe that we want to use when degreeing the cams to the manufacturer's specifications.
00:25 Under normal circumstances though the VTEC system will run on the low cam lobe so we need to artificially lock the VTEC mechanism in the high cam position.
00:34 There are a couple of ways we can go about locking the VTEC mechanism.
00:38 Since the VTEC system is actuated by engine oil pressure, we can replicate this using a supply of high pressure compressed air which can come from our normal workshop air supply.
00:51 On the B16 and B18 Honda cylinder heads, there's a blanking plug for an oil gallery in the cylinder head that can be removed and then we can screw in an adapter that will allow us to connect this to our compressed air supply.
01:04 There's also a hole on the inside of the cylinder head that we will need to blank to prevent the air just leaking out.
01:12 Once we've done this, the compressed air can be used to force the VTEC system to remain engage while the cam timing is checked and adjusted.
01:21 An alternative option is to disassemble the rocker arm assembly and remove the rockers for the intake and exhaust valves on number one cylinder.
01:29 The VTEC system is actuated by a little spring loaded pin that's forced out by oil pressure and locks the three lobes together.
01:37 By temporarily placing a spacer behind this pin and reassembling the rocker gear, the VTEC system will now be locked in permanently.
01:46 It should go without saying, but once the cam degreeing process is complete, it's important to revert the VTEC mechanism to stock so that it can operate as Honda intended.

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