THE BOXER
BRIEF !
THE ENGINE BUILD....
OCTOBER 2015 QUestions ...
1) Where do Corvair cases/heads/parts come from? Are
they all from the 1960's? How do you confirm that they are
"airworthy.
There are a few ways that we use to confirm the
use and airworthiness of a particular corvair engine part.
We will tackle the two parts you mentioned above today.
The majority of the heads and cases are from cars built from
1964 to 1969. For those building their own engines there
is a listing of the model number most appropriate for aircraft
use. We have a list of those in our Teardown
Manual.
Initial condition: If you are tearing down an engine core
that came from a running engine and/or the engine turns over
easily, good compression, and clean, there may be higher odds of
finding core parts in good condition. Once stripped down,
you can begin the cleaning of the individual parts and start
looking for....
CASE: Once the case is apart and the
engine model code is verified to be usable for the conversion
get your cleaning supplies (purple power spray bottle and a
stiff britle brush) and begin soaking and cleaning the grime off
the case. I will soak the parts and come back every
fifteen minutes and spray down the part for the whole day and
toward the end of the day wash the parts off. This lets
the spray soap do its work. Other options are taking
the case to NAPA or similar machine shops and having the case
professionally cleaned... As you clean the case you will
notice more about it. On the case we look for hammered out
main bearing saddles (not to typical) and highly scored cam
bearing surfaces. The other thing we look for are damaged
lifter bores. We have run into many cases that have
factory repairs, welding or lifter sleeves, but the quality of
the work will be good. If you have concerns shoot us a
picture. We have orginal drawings and dimensions so we can
check out bearing saddles for out-of-round and more.
For the most part the cases hold up real well. Head
studs can be bad, bent, corroded and more and we have to remove
and replace them.
HEADS: On the end of the heads is the
casting number. Verify the appropriate head for the engine
you want to build. We typically use any of the late model
95 HP or 110 HP heads. However, we have capabilitied here
to modify some early heads for custom work and have several
engines flying with them. Again, it is best to
dissassemble the heads and valve assemblies for a proper
cleaning. We look very closely at the combustion chamber
for any signs of corossion and overheating. (pitting or
deap imprints from the head gaskets) We usually have to
set up our mill and flycut the chamber bores slightly to reset
the gasket area. If the heads are really nice and the
seats look good will will normally leave them in place. If
there is any question about the seats we replace the intake
seats with deaper seats. New bronze guides and a three
angle valve cut with new stainless valves and springs bring the
heads back to good condition. If requested we also mill
off the original carburetor pad and weld on intake pipes for our
manifold. We process lots of heads here at the shop.
It is not a job for the untrained....dont let that stop you from
learning though :)
SEPTEMBER 2015 Questions....
Do you recommend regular oil analysis for the Spyder
engine?
An oil anysis is typically a situation where you
send an oil sample to a lab and they respond with results of
amount and types of materials found in the oil. If the
copper content is high it may be a sign of premature bearing
wear. If bronze is high - maybe guide wear and so on.
I have not done these types of tests because I usually open the
filter after an oil change and look at the pleats - or wash the
material onto a clean paper and look it over. By running a
small magnet over the material you can determine if there is
metal wear. Non-ferous material can be checked by color
and type of material. I find that an analysis will
only find something I can spot in the filter inspection.
I dont recomend using oil analysis before the first 100 hours
because there is a lot of initial break-in wear that will give
you false results. If you establish a base line and
monitor from there then it is a good procedure. Because of
the kind of flying and maintenance I do I don't perform oil
analysis on my planes. One reason is becasue sometimes I
change the kind of oil I am using to check cooling and
lubrication properties and its hard to have a base line when you
change the oil type midstream.
Is it reasonable to convert the 100HP Spyder to the
120HP version? Do you have any details/recommendations for such
a conversion?
There are some major differences between the two
engines, however, it is an easy conversion. Take the 100
off the mount and bolt the 120 on! The 120 has a
new, counterweighted and stroked crankshaft, new design rods,
and new design pistons. Is is much more cost effective to
build a 120 and then swap out. We will pro rate any of our
engines for exchange or come up with a equitable exchange with
any customer of ours or even with people changing from a
competitor design to ours. All of the auxiliary or
FWF parts are similar between the two engines and don't have to
be changed. What can you expect as part of the exchange?
You will probably have to change out the propeller or change
pitch but not absolutely necessary (depending on installation).
Expect that CHT's would be slightly higher on climbouts -
however you could get to altitude more quickly and then throttle
back to cruise configuration where temps will stabilize.
Any given power setting will give you higher performance however
remember that the airplane will perform the same at same RPM
(with same prop).
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