"Del Johnson wrote:
I just read the note on Flinns melting engine mounts and
realized that I
might be going down the same road. I just finished, with the
help of a
friend the welding of the engine mounts for the Glastar. The
front portion
of the engine is supported by an aluminum plate that attaches
between the
block and the oil pan. <snip>
Let me take this one step at a time.
First here are some of your pictures.
The basic steel tube structure looks excellent. You can save a lot of
weight by going to a Schertz Beam type mount. The difference is the
Schertz Beam requires a custom oil pan and is mounted under
the oil pan flange and not on top of the oil pan flange.
The original was made from 1 by 2 rectangular 4130 tubing
0.065 wall but a 4130 steel channel could be used if you ware willing to
brace it up to the engine.
Paul Lamar
Here is a better picture showing the pan bolt spacers.
If a 4130 steel channel is used these can be done away with.
Note the notch in the oil pan to accommodate the Schertz Beam
mounted below the oil pan flange and NOT above the flange.
<snip>
Those 6 small bolts that go into the block look awful small and short in
thread length? I realize most of the weight is downward. In a I'm not
going to be doing aerobatics in the Glastar so it is less of an issue than
with the RV folks. I don't have any 'warm fuzzy' feeling about the method
of mounting it. Side bracing using steel channel would allow tying into
some large bolts off of the bell housing mount and/or the intake manifold
studs.
If I went with Channel Steel and bracing, what size/thickness is
recommended?
Well if you brace it there is no vertical bending load to speak of so a 4130
sheet channel formed up about 2.25 inches wide and one inch deep
should be over kill .050 thick. Each one of those 6 mm screws should take
about 2500 pounds each in shear at a stress level of 60,000 psi.
About the same as a 1/4 inch screw. Six times 2500 pounds is
15,000 pounds so I would not worry too much about them.
Paul Lamar
But you're worrying about a 900# bending load on my 3/8" bolts (22500+ pounds strength).
Actually my bolts sit in a 1/2" OD steel tube, and with the new Barry mounts those will sit in a
3/4" steel tube. Paul, one of these days you'll have to learn that it's not all black and white:
there is a range of "workable" in-between "ideal" and "doomed to failure". Maybe then you'll stop
unnecessarily alarming people.
Finn
Where did you get 22500+ pounds strength?
The area of a 3/8 bolt is .110 square inches.
At 150,000 psi that is 12,000 pounds shear strength.
Not 22,500 pounds.
That is the shear strength of the 3/8 bolt not its bending strength.
The fact that the bolts are in a 1/2 inch steel tube has little to
do with it. The weld integrity between that tube and the wall thickness of
the long top and bottom motor mount tubes have a lot more to do with
it.
Finn it takes a life threatening event to get your attention.
We have seen that over and over again in the last four years.
Mere words don't seem to affect you. I frankly don't care
if you kill yourself. :-) Just don't do it in a rotary powered
airplane.
Maybe someday you will use that excellent brain of yours to study
space frames and you will then understand how stupid that motor
mount design really is.
Paul Lamar
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