Valve Adjustment on Mazda Millennia with Miller Cycle Engine

The Mazda Millenia S 2.3L is not a difficult to repair car. By that I mean that service or repair of the Millenia 2.3L does not require any special tools or knowledge beyond that which a good mechanic will already possess. It is; however, a very time consuming car to repair, that along with sky high parts prices, makes it a very expensive car to repair. This valve adjustment will set you back almost $900 and take 2 to 4 days.

What’s this a picture of? It a jumbled mess! You can’t tell what’s going on. There are connectors and hoses and solenoids and brackets and harnesses in a big heap. All of this stuff blocks access to the valve covers and must be removed before doing a valve adjustment.

a jumble of wires, hoses, and cables

Next the pipes and valves for the supercharger must be removed. 41 seals, gaskets and o-rings are required to do a valve adjust.

intercooler and intake ducting

With all of that out of the way we can now see the supercharger and, of course, the valve shims and cams.


The valve clearance is the distance between the cam lobe and the valve shim when the tip of the valve lobe is pointing away from the shim. The clearance is measured using feeler gauges, which are thin strips of metal marked with their thickness in thousandths of an inch. The feeler gauges are tried one at a time until one is found that matches the gap between the lobe and the shim. If the clearance is found to be wrong, the shim is removed and measured. If the clearance is too great, desired clearance is subtracted from the actual clearance and added to the current shim thickness to calculate the correct thickness. If the clearance is too small, the current clearance is subtracted from the desired clearance and subtracted from the current shim size. For most cars we have a supply of shims on hand, but for the Millenia, the correct shim must be ordered from the dealer, which means the engine will have to sit apart for 2 days while we wait for the shims to arrive.

camshaft and shim buckets

These are two of the ignition coils. The one on the left was wet with motor oil from a leak from the spark tube seal. The coil was still working OK and the leak that had been soaking it was being fixed. We cleaned the oil up to prevent any further damage and moved it to the front bank where it would be easier to replace if it did develop a problem.

Two ignition coils. One is oily