ProtoConVert

So if i remember the tech highlights cd that was goin around a few months ago, there was this interactive simulation that reported a compression test...

what exactly do the results of this test indicate about the engine and its components, like what is a low compression symptomatic of, and are the types of problems with low compression fixable w/o a rebuild?

eccles

Checking the compression on a rotary is not as straightforward as a piston engine, because the measuring point (the spark plug hole) is exposed to three separate compression surfaces per rotor revolution.

In the absence of the genuine Mazda megabuck diagnostic tool, the best substitute for the backyard mechanic is a regular compression tester with the non-return valve removed. This will give a series of pulse readings as the engine is cranked, which allows you to compare the compression of the three surfaces rather than just showing the single best compression.

Remove the plug leads from all four plugs, and remove the leading plug from each rotor. Insert the gauge into one of the leading plug holes and crank the engine for several seconds as you observe the gauge, then switch to the other rotor and repeat.

If one surface has lower compression than the other two on the same rotor, this generally indicates a problem with a side seal; if two are low and one is high, this generally indicates a problem with the apex seal between those two surfaces; if all three are low (compared to the other rotor), you've probably ingested something solid and lunched all three apex seals on that rotor.

If the seal problems are due to physical damage, you're looking at a full rebuild. When rebuilding, it's worthwhile replacing all the seals unless they're very new and undamaged - it's just not worthwhile scrimping on seals to save a few bucks.

If the sealing problem is due to a stuck seal, it's possible that a dose of upper cylinder lube or marvel mystery oil may restore them, but this is rarely the case.