Finn Lassen wrote:

I finally pulled the engine off the airplane.

1) Another broken tension bolt (this time #17 in loosening sequence, the
other one was #8).

2) Blowby. The only evidence of blowby (into water jacket) was between
bolts #16 and 18 at center housing. I'm at a bit of a loss to explain
why. It's not near the broken tension bolts nor does the edge of the
channel/groove appear broken.

3) Both the inner and outer waterjacket o-rings are in good shape, still
soft. The white (teflon) bands are separated from the O-ring, though.
Probably not an issue when in place. Those were Mazda stock o-rings.

4) There is carbon build-up on rotors and on rotor housings near the
"hump". I've been running too rich in the low RPM range.

5) Oil pump chain way out of spec: 5/8" slack or more (limit 3/8").

These are just first impressions. Need to do cleaning and a more
thorough inspection. Haven't looked at oil scraper o-rings yet.

On the subject of tension bolts. I watched Bruce's overhaul video and I
don't recall chasing the threads on the bolts and housings when I last
overhauled the engine. So it's possible that the actual tension on the
bolts were not equal even though they were tightened to the same value.

Finn

Don't get the idea this is a real problem folks. Finn was warned about
removing the bolts and coating them with RTV last summer when Perry Mick
broke a bolt. He failed to do that. It is caused by running the engine
at a constant, high HP, high RPM that may happen to coincide with
a violin string type of resonant condition in the tension bolt.
The exact resonant frequency of course is determined by the torque on the
bolt and the resulting tension on the bolt. The RTV coating
damps this vibration.

This used to be a well known occurrence in Mazda racing engines but since 
Mazda changed the design of the bolts and people starting coating them 
with RTV the problem went away according to Mazdatrix. It is now almost
unheard of in Mazda racing engines.

Paul Lamar
 
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