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1. 02:34 AM - Re: Airbox for 912S (Richard Holder)
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| Subject: | Re: Airbox for 912S |
On 05/09/2020 16:01, Steven Pitt wrote
> <stevenwpitt@me.com>
>
> Now I have a dilemma. I have measured the diameter of
> the inner carburettor at 45mm. The airbox outer tube is
> 48/49mm - the inner diameter 39 and 42mm (these
> measurements after my fix - several layers of bid to
> strengthen the orifices after they collapsed under the
> tightness of the worm driven band).
>
> I have never had a problem with the carburettors and
> never given any thought to a mismatch between the two
> diameters. I was always aware the the box was poorly
> finished and the air intakes were easy to crush, but
> with the bolt holding the box to the engine frame it
> had never departed giving me an inflight issue.
>
> It is also notable that the two orifices were not the
> same size even before the collapse.
>
> The only way I can see to equalise the two is to
> rebuild the airbox as per Dave Ps suggestion - cut the
> ends off - find an aluminium tube with inside diameter
> of 45mm and bond that in with bid. Anyone got any tube
> to that size?
>
> Anyone else wishing to add any advice before I carve
> the boxes up. Also what is the airbox made from? It
> looks like chopped strand mat fibreglass.
Steven, just seen this.
When my airbox tubes compressed I used short lengths of
steel exhaust pipe with the correct OD (to match the carb
inlet OD).
I dremelled away enough of the original fibreglass to get
the exhaust tube (ET) to fit nicely using the carbs as the
locational template. I drilled a few holes in the ET to
allow keying. I then resined (with a filler) in the ETs
without worrying about the actual orifice size.
When the resin had gone off I dremelled out all the
surplus resin on the inside leaving it reasonably smooth.
Much stronger than the original, and as the air passage is
now much larger than it was the engine runs less rich !
And I can do the Jubillee clips up tight. I bought short
lengths of silicone hose with ID to match the carb inlet.
Not patented !
Richard
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