I just spent some time looking on the internet for negative comments
about JB Weld. I did not find any. One testimonial, a guy repaired
a gouged cylinder wall and ran the engine for several hundred
hours. Tear down showed no change or deterioration in the JB
Weld. Also, JB weld claims the product is good to 500 degrees.
Based on what I have learned today, I think my skepticism about JB
Weld was misplaced. Jerry
Jerry,
If your considering manufacturing P-ports, you might consider a
slightly
tapered shrink fit of the tube within the housing with some high
temp epoxy
to take up and imperfections in the machining.i.e. heat-up the
housing and
freeze the tube - his would take some experimentation to find the most
suitable size whereby you can still get the tube inside the housing
and this
would all need to be done on a CNC for the accuracy needed.
This would be the most ideal method of sealing, but how practical it
would
be I'm unsure!
Just a suggestion, as it's something I'm considering..
George ( down under)
Hi George;
I did my Pports as you are suggesting with the inserts all the way
through with
match tapered (smaller towards the inside of the housing) insert and
bored hole
and an interference (hot rotor-cold insert) press fit with epoxy on the
prepared insert
bored hole.
One advantage is that it should never fall into the engine.
One disadvantage is that the 2" ID is rounded to 2.125" on the rotor
surface - I am
not too concerned about the slightly reduced apex seal support as the
edges are
beveled to soften the apex seal landing back onto the rotor surface.
This measuring and fitting took significantly longer by hand using a
basic mill, lathe,
digitial calipers and sandpaper...and lots of measurements.
The interference can be figured out easily enough looking up the
material and
temperature differential you plan to use between the housings and
inserts.
One press fit did take a little more convincing with a mallet and wood
block ;)
I machined the inserts as well, finding the correct sized tubing could
save a lot of work.
Without starting an epoxy war...
One of my biggest concerns is the ability of any epoxy to bond to
aluminum with less than Boeing processes.
Any bond can fail for a variety of reasons - poor surface prep, surface
contamination, poor epoxy prep,
differential thermal expansion at temp, chemical resistance, vibration,
thermal stability at higher temp (say 300F),
epoxy cure shrinkage, and for northern residents - differential thermal
shrinkage over the winter months.
In any case, some sort of mechanical assistance/backup to the epoxy is
not a bad idea - threading, brazing,
welding, press fit, pins, extra mechanical bond area (grooves, etc...)
to insure the insert does not fall into the
engine catastrophically without warning. A leak would be annoying, but
hopefully less dramatic and with warnings...
Take a look at an interesting article by Bill Husa regarding bonding:
http://www.oriontechnologies.net/Documents/bonding.pdf
To summarize - sanding the aluminum surface with epoxy already on the
surface may help adhesion by removing
and preventing the oxide layer from reforming.
Cheers
Cary
Cary,
I was thinking of a slight taper on both ends with the tube being
mechanically locked into position and the thin high temp epoxy only
being a
( surface imperfections) void filler, in the tapers and of course the
water
cavity.
This would be extremely difficult to do as your measurements would
need to
be exact AND you would get only one go at it.
The benefit would be that you would never have to worry about the tube
moving either way.
I have looked at the threaded inserts, as done by X-Treme Rotaries, but
others suggested that it wasn't optimum.
Is nothing ever easy!!
George ( down under)
Anodizing or etching improves the bond but IMHO it is not necessary.
However some very small groves on the OD of the tubing
about .020 inches deep would also lock it into the housing.
If one were worried about the bond use some JB weld to
bond three pieces of .065 thick aluminum together that
have roughly two square inches of contact area. Say two inches
long by 1 inches wide. Say something like this.
Hole
__________________
^ ___________________
__________________ ^
^ -------------- Hole
Hole
You need three pieces to load the bond in pure shear to emulated
the pure shear the tube would experience in the bored housing.
Two pieces would cause a peeling action due to out of axis
loads.
Then use this and an engine hoist to pick up something heavy.
My guess is the aluminum will fail before the bond shears.
Paul Lamar ...No rotor no motor.
Hi Paul,
I agree with you regarding the strength of the bond on a large surface
area such as these inserts.
I don't mean to scare anyone. No need to do a double shear test.
The largest stress this insert will see is differential expansion -
unless you drop the engine on the intake.
I only mentioned the mechanical backup because we should be thinking
about all failure modes - a
straight through insert should consider this failure mode as should
filling the sideports.
My most likely failure mode is leaks...
Cheers
Cary
As I mentioned to George a little tig tact to the out
side part of the rotor housing should be OK if you want
a mechanical connection. Actually the intake side of the engine
runs very cool so there is not a lot of differential expansion
going on. Another way of doing it is weld a flange around
the tube and use a couple of 10-32 machine screws.
That is what Everett Hatch did.
Paul Lamar ...No rotor no motor.
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