snips...

Easier still is to use an aircraft vac. pump and small toothed belt.
Ian.

Not really Ian. Aircraft vacuum pumps have no provision for bearings
of any kind. A toothed belt chain or any other kind of belt drive
will produce a side load on the vacuum pump shaft. They normally drive off

the

accessory gear case on the back of an aircraft engine. That means you
must machine a mounting block and a properly supported auxiliary shaft
to mount the aircraft vacuum pump. Its been done. Back in 1991
Tim England had a Velocity with a GM 4.3L V6 at OSH with a Singer
sewing machine flat belt drive aircraft vacuum pump. I got a picture
of this around here someplace but cannot find it right at the moment.

In the mean time here is the bearing requirements for a belt drive.

Paul Lamar

Tom Kendall wrote:

Hey Paul, the drawing and torque numbers you posted can be a bit misleading
since we're talking about driving just the vacuum pump and other accessories
(like an alternator or water pump).  The drawing is referring to side loads
to carry the entire engine output.  For the accessories, the side loads are
very small fractions of the 900 lbs cited.  Use whatever horse power each
accessory requires to determine the side load due to torsion.

But it's a bit more complicated than that because each accessory is an
"overhung" shaft arrangement, meaning that both bearings are to one side of
the radial belt load instead of straddling it.  Also, belt tension will be
through different angles for different belt arrangements.  If somebody has a
specific proposal, post it and I'll give her a shot on what the bearing
loads will be.  I'll need the angle the belt is making contact through, and
two of the following three : rpm, power, or torque needed for the accessory.
List all of the accessories on any one belt, along with the requirements for
each.

I agree fully Tom. Its just the drawing I had. Yes you need two bearings
in the adapter. Or a two row ball bearing like a water pump bearing.
Something similar to this.

Paul Lamar
 
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