ctgottapee wrote:I looked up the procedure to check valve clearance on the gen2 2.4L models and it looked fairly intense. For a shade tree mechanic it appeared I risked damaging things far more than just checking would provide.
I just looked at the 2AZ for a highlander. You just pull the valve cover, set it to crank at TDC with the cam marks aligned like the procedure shows, and use a feeler gauge to check clearances between the heels of some lobes and the lifter buckets, then turn the crank one more full rotation and repeat on the other lobes, as indicated.
It doesn't get intensive until you find one that is off. Keep in mind that there are tolerances (min and max acceptable). At 100k miles, mine did not need it although one single clearance was at the max acceptable. I was installing new cams, but the heels and lifter buckets are your criteria, so that shouldn't change anything as the heels shouldn't ever touch anyway. Can't remember if I said that or not and I'm really tired. Only the toe of the lobe and the intake bucket on these cars should get any wear because those are the only parts that should ever touch, otherwise the valve would always be a little bit open no matter what.
What you are measuring is the distance between the heel (part of the lobe not meant to open the valve) and the closed valve's lifter bucket. You are checking the wear on that bucket, which will need replaced with a certain size bucket to bring it into spec (if it is found to have unacceptable clearance). For every full turn of the crank, the cams make 1/2 a turn. This is because you have the two strokes with the piston at TDC (exhaust and compression), and two where the piston is at BDC (intake and power strokes). The cam needs to make a 1/2 turn because 1 full turn opens the valve when the toe reaches the valve, and you only want open valves on the intake stroke and the exhaust stroke. Since these cars are DOHC, you don't have the exhaust and intake valve timing directly linked. VVT-i allows the intake cam to advance timing only on the intake side on the 1st gen 1ZZ and I think 2ZZ. Dual-VVT-i adds in the exhaust cam being able to vary timing in addition to the intake side.
Does my silly explanation help or make sense at all?
EDIT: Other cars have different ways to activate the valves; I only explained the way for the 2AZ and 1ZZ. The 2ZR uses hydraulic self-adjusting lifters. Some engines use long lifter rods, some use rocker arms (including the 2ZZ), and some use tappets. I don't want to explain additional valvetrains right now.
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