Thanks Lynn for the technical info; I had not seen been to that
website before … Racing Beat I am well aware of. Actually I bought one of their
double alternator pulleys, which they claim reduces rpm by 20% … other than
aluminum instead of steel it is same diameter of existing pulley. I’d like to
change it anyway for the small weight gain and what-if due to belt breakage …
but I can’t get the nut off … any hints?
Jeff
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Lynn Hanover
Sent: Monday, December 01, 2008 9:46 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Hot first flight
Thanks
to you all for the congratulatory comments … attached is a picture of expansion
tank and preflight roll-out … the orange line is fuel return; the brass is
pressure gauge pickup and snifter valve installation.
After
reading Eds' email I now know why the water temperature was so high. I
installed a thermostat with the onset of cold weather, but I couldn't use the
original Mazda thermostat because my temperature bulb protrudes across the
bypass hole. Originally the bypass hole was plugged and there was no
thermostat; however, I removed the bypass plug and used a non-Mazda thermostat
!! … so that's why the underside of the Mazda thermostat is so long! Thanks Ed
for setting me straight and based on your comment about 20% loss of efficiency,
I could possibly see 230F x 0.8 or as low as 184F on next flight … that would
be great! For now the thermostat is gone and bypass is re-plugged.
Closer
examination of the belt and rubber deposits on underside of top cowling suggests
the belt got jammed in the pulley and cut by friction.
I
tried again last night to remove the alternator pulley nut … what's the secret?
Left-hand thread? Loctite or what? It's so tight I'm afraid of damaging
something trying to get it off.
Jeff
Belt failures are in modern times, a very rare occurrence. Dual
or multiple belt installations are generally found where a single belt would be
operating at close to maximum capability and so are servicing the same pulleys.
Multiple belts servicing some different pulleys are not in this class.
For same pulley installations multiple belts need to be matched
sets. The Government uses thousands of sets of matched belts for large diesel
trucks. Some with 3 or 4 belts each.This is not a redundant system designed for
reliability. In any case where a belt is run to death, or rock damaged, the
remaining belt(s) will often fail in the same instant by ingesting pieces of
the failing belt, it that is not the case, the remaining belt(s) will fail just
from operating close to their load limit. In every case, one must
assume that the companion belt has suffered some damage, and it wont match the
length of any single belt installed along side it, so it (they) remaining belts
should be discarded.
If there is not an obvious FOD cause for the failure, the
installation should be checked carefully for alignment, tension and
stiffness (rigidity) at high RPM. Also with accessories loaded and unloaded.
The crank nose on the rotary is a weak point, and can fail right
at the front main bearing if the belts are over tensioned. Note the mass of
pulleys found on some years of the cars. The single or double pulley in small
diameter mounted close to the front cover, is less prone to failure just from
the lever arm difference. On assembly it is common to torque the pulley bolt to
95 foot pounds as this stiffens the stack of items clamped in place by the
bolt. You must then check crank end play at the same torque, as some end play
is used up when this is done. There is a belt length that fits between the
water pump and crank pulley with the race pulley set, that fits perfectly with
no idler. I discarded the first such belt after three years, although there was
no sign of wear at all, other than the writing was gone.
Also: From Mazda Competition,