Steve,
The bing 64 has a 50mm OD inlet for the filter or airbox attachment. The bore
is nominally 36mm.
The airbox (aka really cheap polyester chop and glass bit from Europa) have ends
that attach to the carb are 50 mm tapering up 52 mm ish. The chop on some of
these is so bad I had to reinforce it for the pop rivets on the nutplate it
shattered so bad.
Jeff Roberts was the first I had seen modify his airbox due to cracking. It
appeared
he used a piece of two inch aluminum tubing and slid it into the well ground
out holes in his airbox and aligned the tubes with his carbs and allowed
the floxed tubes to cure, then wrapped the glass around the tube outside the
rubber tube to final bond the outside of his tubing.
I copied Jeffs later on using the 1 7/8 inch aluminum tube left over from the
main
pitch rod. I ground out the cracked airbox and inserted the 1 7/8 (47.6 mm)
tube with flox and Redux (any epoxy will do) and then wrapped layers of bid
around until I was about 50 mm or 1 15/16 inches diameter. Then shaped to get
an easy fit of my two inch rubber hose. I was OK with this method since the
connecting hose allowed the two inlets on the bing carb inlet sufficient clean
air for normal operation. On a later aircraft I used 2 inch tube. The hose
clamp clearly compressed the hose more on the carb side than on the inlet box
with the two inch tube.
Epoxy sticks to just about anything but oil and grease so it will make a good
repair
bond to the clean and roughed up polyester without a problem of bonding.
Remember to rough up the aluminum as usual also.
So you have two methods, either an innie or outie method.
Note: The airbox does not have to be really smooth on the inside. It is a
plenum
not a tuned inlet. The bing carb sucks air rather than ram air entering the
carb on the 912S. The transition humps and bumps should be minimized but just
make both ends about the same and all will be fine. Remember, the bing has
an inlet on the inside above and below the bore so make sure they can get
reasonably
clear air...
Of course Rotax wants you to buy their $1000 intake plenum. The only problem is
it tends to lack support and since it hangs on the carb, it cracks those
expensive
43mm rubber carb manifold to carb flange. Support the inlet plenum, that
supports the carb and those rubber carb flange adapters last almost forever.
Just my opinion,
Best Regards to Mary also,
Bud Yerly
Best Regards,
Bud Yerly
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