<VV> Running an engine without shrouds

Wed Sep 23 18:26:17 EDT 2015

Hi Bob,

You're welcome.

Please keep in mind that much of what I write is for general  reading.  
Others' may be in a similar situation to yours some  day.

As far as your engine stand ... it sounds very sturdy.   However, the 
danger is not so much how much weight it can support as it is the  geometry.  
Please keep in mind that I have not seen your stand.  Your  father may have 
built it with a running engine in mind so, again, this is for  the benefit of 
all.

Regarding the geometry, most stands are configured with a 3  point stance.  
My stand has 2 wheels fairly far apart at the back where the  motor mounts 
to the stand.  It also has 2 wheels at the front.   However, those wheels 
are much closer together.  It is close to a 3 point  footprint.  The area of 
concern is how high the center of gravity is and  how far apart the footprint 
is from side to side.  The stance/center of  gravity combined with the 
torque created by an accelerating or decelerating  motor can cause the rig to 
tip over.  The weight capacity of the stand is  irrelevant.  To further 
complicate things, the effective stance from side  to side is not the widest width 
of the wheels because the footprint is probably  a triangle.  To get a 
general idea of the effective width of the stand's  stance, draw imaginary lines 
from the back wheels to the front wheel or  wheels and then estimate where 
the center of gravity is for the system from  front to back.  It will 
probably be close to the center of the motor.   The width between the imaginary 
lines at the center of gravity is the effective  width of the system.  If you 
have the math background you can calculate the  kind of torque from the 
motor that can cause the stand and motor to tip  over.  It probably isn't that 
much.  Here are some suggestions  ....

1.  If you choose to run the motor on the stand, do not  accelerate the 
motor too fast.  Bring it up to speed slowly.

2.  Do not just let off on the gas too quickly  either.  Deceleration 
torque can be a problem too.  (Brake  horsepower/torque.)

3.  You can put some sandbags on the spread legs of the  stand to 
effectively lower the center of gravity.

4.  To avoid the "I should have listened to Doc." moment  after the fact, 
just don't run the motor on a stand.  Lower it to a pallet  and be safe.  I 
have no doubt that stand manufacturers put warnings on the  equipment that 
you shouldn't run an engine on the stand for just the reasons I  have 
discussed.

5.  Just in general, when you mount a motor to a stand  like this, try to 
get the axial center of mass of the motor as closely aligned  with the 
turning center of the stand as possible.  If the center of  mass of the motor is 
too far above the stand's turning axis the motor will want  to turn itself as 
soon as you remove the holding pin from the turning  point. This could 
cause the stand to tip over too.   If the  center of mass is too far below, you 
will have difficulty turning it 180  degrees. This is not too much of a 
problem with our diametrically opposed motors  but a V8 or water pumper 6 
cylinder could ruin your day if not properly  positioned.  Keep in mind that as 
you remove or add parts such as heads,  crankshafts, etc., the center of mass 
will change.  With our motors, if you  have the heads and cylinders removed 
from just one side, the system will want to  swing itself as well when let 
loose.

Be safe,

Doc
'60 Corvette, '61 Rampside, '62 Rampside, '64 Spyder coupe,  '65 
Greenbrier, '66 Canadian Corsa turbo coupe, '67 Nova SS, '68 Camaro  ragtop
~~~~~~~~~~~~~~~~~~~~~~~~~~~

In a message dated 9/23/2015 2:23:55 P.M. Pacific Daylight Time,  
bgilbert at gilberts-bc.ca writes:

Thanks  for the comprehensive reply. Much appreciated. 
It  will be mounted on an engine stand but not one purchased. It was made 
many  year ago by my father and it is VERY sturdy. The main bearing that 
holds the  engine is almost a foot in diameter  and was originally the hub from 
a  large bulldozer wheel. The frame is from thick walled 6 inch pipe. In 
past  lives it has supported heavy diesel engines; my father built things to 
last!   
The  stand will be in my garage right by the door with the dual exhausts 
supported  and extending about 8 feet outside the door.  
All  I want to do is run it for 15-20 minutes or so at 1500 RPM or so and 
make sure  that there are no leaks or anything else not as it should be 
before I remount  it in the UltraVan. Getting it in and out of the UltraVan is a 
lot more  difficult than a car due to the much tighter clearances in the 
UltraVan. I  just want to make sure that, before I put it in that I have done 
everything I  can to make sure it is going to be OK.  This is engine 
installation  number 3 in this vehicle and I really don’t want to do a  4th. 
Regards, 
Bob 

From:  RoboMan91324 at aol.com [mailto:RoboMan91324 at aol.com] 
Sent: September  23, 2015 10:11 AM
To: virtualvairs at corvair.org;  bgilbert at gilberts-bc.ca
Subject: Running an engine without shrouds  

Bob,

Yes you can.  ....  on the following assumptions.

You said "before I  install it."  I assume you are running it on a pallet 
or other test  bed.  If this is the case, I don't see how having the shrouds 
on or off  will make any difference.  Installed shrouding inside an engine  
compartment is designed to pull air from a particular direction and seal off 
 from other directions.  The engine being free of the engine compartment  
will allow the fan to suck from anywhere with or without shrouds.  With  the 
motor "hanging out there" the cooling may be better.

On that note, I assume  you are talking about motor to body sheet metal, 
right?  That assumes  that the other sheet metal between the heads, turkey 
roaster, etc. is  where it should be.

I assume you are not  going to run it under heavy load.  If this is the 
case, cooling needs  will be minimal anyway.  The thermostat controlled 
shrouding under the  motor will probably not be necessary for test purposes.

Keep in mind that the  shrouds are there to duct fresh air in from the top 
of the car or sides of the  FC so you aren't sucking up as much road debris. 
 In the summer,  the air from above is usually cooler than the air that 
might be pulled up  from just above a hot roadway.  Also, the factory system is 
designed to  minimize sucking in exhaust fumes.  While the exhaust fumes 
issue would  cause minimal problems for cooling, you don't want that stuff 
circulating  through your passenger compartment heating system which comes off 
the  motor.  Exhaust from running the motor for test purposes shouldn't be a 
 cooling issue but make sure you don't run the motor in an enclosed  
garage.  People die that way ... and quickly depending on the garage  volume.

Not to be morbid but  running a motor in an attached garage can be deadly 
to everyone in the house  and not just the garage.  This is especially the 
case with people (and  pets) already suffering from lung ailments.

Lastly, I don't know  what your test setup looks like.  If you try to run 
your motor on an  engine stand and give it a hardy goose of the gas, the rig 
might want to flip  over with resulting disaster to the motor, your knees, a 
fender, etc.   When the rotating mass (flywheel, crankshaft, etc.) wants to 
accelerate in one  direction, the "stationary" mass (block, heads, 
cylinders, etc.) wants to turn  in the other direction.  You have probably seen a 
motor in an engine  compartment tilt over when you give it a good shot of gas. 
 The only  thing keeping the engine from spinning wildly in the engine  
compartment are the motor mounts attached to the significant mass of the  car.  
A motor on the floor strapped on a pallet is much more stable than  one 
sitting up in the air on a stand that may be a bit wobbly to begin  with.

Be careful,

Doc

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~