I have recently had to rearrange my valve lifters in order to tune to an optimal clearance between cams and lifters, which on my Tacoma is 0.15-0.25 mm for the intake and 0.29-0.39 mm for the exhaust valves. I had performed multiple rounds of measurement meticulously and had to order some new lifters as some valves were so much out of the range that none of the existing lifters (which come in different gauges) would close the gap.

But I did it because I had my cylinder heads open and had easy access. My question is, how does an engine that has loose or tight valves manifest the anomaly? What are some of the symptoms by which you'd know that you need to tune your valve clearances?

  • In a word ... "noise". Other than that, I'm not sure. I'm sure self destruction needs to be thrown into the mix as well. I haven't dealt with the OHC Toyotas, so take what I've said with a grain of salt. I would bet @Movemorecommentslinktotop would have a much better answer for you. – Pᴀᴜʟsᴛᴇʀ2 Sep 1 '15 at 22:18
  • as for the "gran of salt" the Toyota tech manual (by Toyota, not Haynes) says to measure the clearance with feeler gauges and replace any lifters that are out of spec – amphibient Sep 1 '15 at 22:20
  • What year is that Tacoma, I've had a few and have torn into a bunch of different years since 1994. – DucatiKiller Dec 8 '15 at 15:00
  • @DucatiKiller, 2007 – amphibient Dec 9 '15 at 21:34
  • 1
    Love 'em, I had the 2006 for awhile, with a 6-speed manual. Great truck. – DucatiKiller Dec 9 '15 at 21:37

Engines absorb valve clearance by having their valve faces pounded repeatedly into their valve seats for tens of thousands of miles. This ongoing operation pounds a groove into the face of the valve where it makes contact with the cylinder head on the valve seat. As the valve face has the groove pounded into it takes up valve clearance up at the top of the stem. The valve 'settles' into the head, if you will. When this occurs and clearance is taken up a valve adjustment becomes necessary.

With four valve heads and a lighter valve with a lighter valve spring and a smaller valve face, maintenance increase. Less force, less weight, less damage over time. This is one of the primary drivers in extended maintenance windows in all vehicles since the mid '80's.

Valves loosen at the stem, depending on what is pushing down on the stem the wear is a variable. If you have a rocker hitting a point on stem directly it will pound it down ever so slightly creating concave point at the end of the stem. If it is a shim and bucket valve train the force is distributed across the entire top of the stem and wears down CONSIDERABLY slower.

Hope this helps, cheers.

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