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Re: [FlyRotary] Engine Failure modes was Re: [FlyRotary] E
Hi Ken,
SIDE HOUISNG WARPAGE
Just have a look at say the centre housing in
particular. The water gallery is about 1.5" away from the edge of the hole
where the E-Shaft goes through. It is also not of constant
thickness. So the main cooling on this area is the spill of oil out of the
rotors. Lose the cooling spill of oil from the rotor and as I
mentioned, they buckle like a belleville washer as this part gets
hot, and the outer part in contact with the coolant remains at the
constant temp of the coolant.
When the engine is stripped, most of the
scuffing is close around the hole. This is because the rotor is
slightly thicker close to the eccentric shaft. The rotor gear sits
slightly proud of the rotor side face and there is an equivalent raised land on
the other side of the rotor. In fact,
according to Mazda, standard clearance between the rotor and the side
housing is only 0.15 mm, which is about 6 thou for you SAE trained
people. So when the rotor gets hot and expands, and the side
housings buckle, it's "good night nurse!".
MACHINING
Over the years, I have had various people
machine my side housings. A Blanchard is ideal, but few
engineering shops here in OZ have such an animal, let alone know what
one is!!. Alternatively, for some time, I had a saw blade
specialist do them for me on a vertical "SNO" grinder (Vertical spindle, and a
horizontal oscillating magnetic table). This guy went to a lot of trouble
to get me a really fine surface finish, purchasing special fine grit
stones just for my job. and setting the spindle angle as close to vertical
for the final cut so that the surface wasn't dished. His table was
huge, and he used to do several housings at a time. Indeed,
from the witness marks on factory housings, I'm sure that this is the
way the factory do theirs.
However, most of the engineers over here just
use a conventional horizontal spindle surface grinder with an automatic
oscillating horizontal magnetic table. Several machine shops in Sydney do
this on a regular basis. There is also no reason that they couldn't
be machined in a lathe with a grinding attachment fitted to the tool
post. I have seen it done that way. Messy, but with the right
setup, it can be done. Obviously it needs a rather big lathe to
swing the housings.
In all cases, to do it accurately, this does
requires special care. It is imperative that the machined surfaces
are at exactly 90 degrees to the bore of the housings. . So for
competition engines, I use a special set of jigs to hold the end
housings, and are set up off the stationary gear bore holes.
Mostly, it will work fine by assuming the bore is square to the back
face. (Obviously it doesn't matter on the centre housing as the hole is
only a clearance hole). However, one bit of dirt, or a
bruise, or a piece of gasket can upset the whole shebang. The back
faces should therefore be carefully stoned with a large flat whetstone to
make sure that they are both clean and dead flat. In particular, ALL
the front cover gasket needs to be scrupulously removed from the front
housing.
Obviously, if the bore is not DEAD square to
the working face, then you end up with a bent motor, and the
eccentric shaft will run at an angle to the bearing bore. The rotors will
also run at an angle to the E-Shaft journals. The motor will then always
be slightly tight, not perform properly, and will forever burn oil
and just be a right bitch. I speak from personal experience!! So
each housing needs to have the bore-to-working-face angle checked after
machining. I have had some personal experience with engineers who are
either not scrupulously clean in their working habits, and/or just
rely on the bore being square to the back faces. Sometimes they are NOT.
I've even had the odd factory brand new housings that have been faulty in
this respect. Sometimes you can see this from the uneven wear on the
stationary gear bearings. The babbitt metal shows taper wear.
So assume NOTHING, trust NOBODY, check
EVERYTHING!!
NITRIDING
Yes, it is always advisable to re-nitride
once the surfaces have been machined. The factory nitriding case is
probably only about 6 - 8 thou and machining will remove most if not all of the
case. I've been successfully nitriding my housings since the early
'70s, even back in the twin dizzy engine days, and well before Mazda
started doing it in 1978. I must give credit to a New Zealand bloke by the
name of Billy Shiels who introduced me to the process in 1974. It gives a
really obdurate surface that is virtually immune to wear, and also ends up
slightly porous, which holds the oil very well.
***
One word of warning. ALWAYS replace ALL the
frost plugs and ALL the oil gallery plugs after nitriding. The heat causes
them to lose their tension. Otherwise, you will end up with a
milkshake in your sump, and it will leak out of all the oil
galleries!! Yes, it HAS happened to me - that's how I
know!!
***
The best process is "Gas Nitiriding" where
the housings are heated to cherry red in an atmosphere of ammonia and
allowed to cool slowly over a couple of days. My current heat treater only
does it on weekends. The housings go into the oven on Friday, and
they are allowed to cool slowly over ther weekend.. It is important that
the housings be placed vertically. If they are lain down flat, the
working faces will end up like great auntie's washboard!
Final preparation is to give them a good
hand lap with some Clover lapping paste. I normally lap two faces
together rather than use a dedicated lapping plate. Make sure you
scrupulously wash off the lapping paste and residue!! Hot soapy
water, a nail brush and some bottle brushes will do the job.
Make sure all the oil galleries are scrupulously clean.
You will also find that the surfaces grow slightly
when nitrided, so it is imperative to clean all threaded holes out
with a quality tap. MY current heat treater has some sort of paint that he
paints on to stop most of this, but it's a bit hard to get right down
inside the through bolt hole threads. So always scrupulously clean out ALL
threaded holes. Otherwise, you will have some REAL fun getting
correct torque settings!
Enjoy,
Leon
----- Original Message -----
Sent: Monday, December 20, 2004 5:10
PM
Subject: [FlyRotary] Re: Engine Failure
modes was Re: [FlyRotary] Engine damage thoughts
My experience has
been that there are 2 basic failure modes when oil pressure is
lost.
Hey leon
I never thought about the side housings
warping and causing the seizure but it makes sense, how and who machines
the side housings, do you blanchard grind them or lap them and do you have to
re nitride the housings after machining them???
I got them kind of housings stacked like cord
wood.
Ken
Welter
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