An extremely informative thread. I recently used @Derf's helpful YouTube video and valve clearance table document to check valve clearances while replacing a leaking valve cover gasket on my 2003 Vibe base model equipped with the 1.8L 1ZZ-FE engine, front wheel drive, and automatic transmission. Mileage at the time of inspection was 173,925. Here's my numbers, checked with a feeler gauge with the engine "cold":
Intake Cam (.0059–.0098")
Exhaust Cam (.0098–.0138")
There was only one valve (I2) that was significantly out of spec, although I had three others which were marginally (.0002") out of spec. The clearances on all valves — both those in spec and out — came in on the high end of the given tolerance range, which I initially found quite believable at the 174K mark according to the conventional wisdom of tolerances increasing with wear.
However, @djb383's earlier post in this thread indicates that the clearances on the "shim type" valve train on these DOHC engines actually
shrinks with wear, rather than growing over time, due to the wear point being the valve seat rather than the surfaces of the shims or cam lobes:
djb383 wrote: ↑Tue Dec 19, 2006 7:45 am
Let me see if I can explain away some of the mystery of a "shim type" adjustable valve train... Here's how it was explained to me. The shims and the cam lobes are extremely hard material and wear, between the two, is virtually nill with proper lubrication. What wears, is the valve seat itself, which is located on the combustion chamber side of the cylinder head. As the valve seat wears, the valve moves up farther into the head, closer to the cam, thus reducing the tolerance (gap) between the shim and the cam lobe. If this gap is reduced too much over time, the valve will be held slightly open and no will longer seal properly against the valve seat.
While this explanation makes perfect sense to my mind, how does it mesh with my clearance results from an original valve train at 174K miles, which indicates many valves at the max tolerance and a few just outside it? Wouldn't this indicate virtually no wear? After all, @joatmon's results from his Vibe at 128K had most of the valves right in the middle of the allowed range:
joatmon wrote: ↑Tue Dec 19, 2006 1:46 am
Today I checked my valve clearance. My 03 base has 128,625 miles on it, so I figured it was due. I had no performance or noise issues that made me think I needed a valve adjustment, but it had been on my list of things to check for a long time. The doc says that the tolerance for valve clearance is:Intake 0.15 - 0.25 mm (0.0059 - 0.0098 in.)Exhaust 0.25 - 0.35 mm (0.0098 - 0.0138 in)My feeler gauge set had increments in 1/1000th inch, and of the eight intake valves, one of them was at 0.007", the other seven were at 0.008". The eight exhaust valves were four at 0.011", four at 0.012". So, all 16 valves had clearances within spec, pretty much right in the middle of the acceptable range, so no need for adjustments in my engine at this time.
For sake of context, I run Pennzoil Ultra Platinum Synthetic 5W-30 motor oil at 5,000-7,500 mile oil change intervals and baby the car most of the time to feed my hypermiling addiction. Car gets 28 MPG in mixed driving with my wife behind the wheel and two kids in the backseat, I can usually pull about average 32-34 MPG in mixed driving with all four of us in the car when I'm behind the wheel, peaking at 36 MPG at 59 MPH.
The reason I'm asking about valve train wear is because I recently sprung a slight leak from the crankshaft front main seal, and am preparing to pull the serpentine belt and crankshaft pulley to replace it. If my valves are already on the high end of the tolerance range and additional wear will
INCREASE my measured clearance, I will take advantage of the overlap in work to pull the timing chain cover, replace the chain, and pull the camshafts as well to shim my valves to the mid-point or low end of the acceptable range.
However, if further wear will only serve to
DECREASE my current clearances, I'll save myself the headache and just slap in a new crankshaft seal. I'd love to hear more input from fellow Vibe owners regarding their experiences on this point and to see more valve clearance check results for sake of comparison.