Yo Kelly,
Attached are a couple of pix of the bolt shanks and
a digital Vernier Caliper which should settle the size issues. The early
12A & 13B bolts has a short thread, and are slightly thicker in the
shank than the the later 12A & 13B bolts, which have a MUCH longer
thread.
The reason Mazda use an M10 x 1.0 thread is so that
the thread will lock under the light tension (27 Ft Lbs). The shank of both bolts is not thick enough to take an M10
x1.0 thread and have sufficient depth. Additionally, they are too
thick to take a 3/8" UNF thread.
The only feasible alternative is to turn the bolts
into studs (see pic), and use an M 10 x 1.25 thread. It's not a
full thread, but is good enough if done in a lathe with a die holder so
that the thread is square to the shank. To make sure it locks, I put
some LOW strength loctite on the thread. I've done several thousand kms
with this motor (half an REW Cosmo engine with 9.7:1 rotor) in the RX7
Mule, and the stud method seems to have stood up to the
rigors.
Other single rotor motors are now in the
process of being assembled, fitted and tested in a couple of Turbocharged
Sports Sedans, and Jet Skis. However, I wouldn't think about
using this threaded stud method in an aircraft though - I'd want a FULL
depth thread.
I did find some cylinder head bolts of a locally
(Australian) manufactured engine that are the correct length, but are
M 10 x 1.25 thread, which do the job. However, they
require the threads in the front housing to be drilled out, tapped and
helicoiled back to M10 x 1.25 - a rather tedious and time consuming task,
and I'm not convinced that the threads will lock with only 27 Ft Lbs
torque.
So I'm currently having some bolts made for both
REW and Renesis single rotor applications (some of the Renesis bolts are
different lengths to the REW because of the side exhaust ports, which just
complicates matters). I should have them available in about 6 weeks or
so. This all should have happened over 12 months ago, but I became
exceedingly ill and nearly "passed over" a couple of times last year. I'm
just getting back into harness now.
Cheers,
Leon