<VV> Running an engine without shrouds

Thu Sep 24 13:45:19 EDT 2015

Bob,

It is likely that if you accelerated and decelerated the motor gently on  
the stand, there would be no problem.  It depends on the accel/decel rate  
and the geometry of your rig.  Keep in mind that when first starting up a  
newly rebuilt motor, you could have run-away acceleration.  Doo-doo  happens.  
It's not necessarily too bad for the motor if you shut it down  quickly but 
it could flip the stand over.  However, better safe than  sorry.

It eases my mind that you chose to run it on the ground first.

To all, please understand that my concern isn't whether or not the stand is 
 robust enough to stay intact under the weight and torque of the motor.   
Bob's stand sounds like it is built to "take it."  My concern is whether or  
not the stand will remain upright.  The issue is Newton's third law of  
motion ....  a universally accepted law of physics.  It  states, "For every 
action (force, torque) there is an equal and opposite  reaction."  The motor 
creates torque to accelerate the rotating members  within the motor, 
(crankshaft, flywheel, etc.) Newton's third law dictates that  the rest of the motor 
will try to turn in the opposite direction.  This  includes what ever the 
motor is affixed to.  I.E., the stand.  An  extreme example of this would be a 
dragster. ... actually 2 examples.  The  torque exerted by the drive wheels 
on the ground will exert a reaction torque on  the vehicle which lifts the 
front of the vehicle off the ground.  Now for  the second and most pertinent 
example.  The dragster's motor is exerting a  torque along the axis of the 
vehicle as well.  If you do a search, you can  probably find a video where a 
dragster is doing a 1 wheel wheel-stand.  The  torque the drive wheels exert 
on the ground lifts the front up and the torque of  the motor on the motor 
mounts wants to flip the car over axially.  You  don't have drive wheels on 
the engine stand but you do have axial torques at  play.  

An assumption I made but didn't state previously is that the engine stand  
uses a pin or clamp to prevent the motor from spinning in relation to the 
stand  while you work on it.  If the pin is there and in place, the stand 
could  flip over.  If the pin isn't in place and you run the motor, the stand  
won't flip but the whole motor will start spinning in the "neck" of the  
stand.  Correction .... if there is no pin and the motor's axial center of  mass 
is mounted off center to the neck of the stand, the motor will spin in the  
neck AND possibly flip the stand as well.  Whatever rig you have to deliver 
 fuel to the carbs will whip around and do bad things too.

Motors are bolted to run-in beds and the beds are bolted to concrete  
floors for a reason.

Good luck with your motor.

Doc

PS: By any chance, do you have a pic of the stand?

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In a message dated 9/24/2015 8:11:10 A.M. Pacific Daylight Time,  
bgilbert at gilberts-bc.ca writes:

Hi  Doc, 
After  thinking about it some more, I’m fairly certain that the stand would 
take the  load and the torque BUT I am not absolutely certain. So rather 
than running  the risk of the engine crashing to the ground, damaging 
something – or worse -  possibly spewing gas everywhere I’m going to err on the 
conservative side and  start it on some 6X6 inch timbers on the floor. 
I’m  still going to use the stand to ease the assembly process. I have done 
that  several times over the years and it worked well. 
Thanks  for the advice. 
Regards, 
Bob 

From:  RoboMan91324 at aol.com [mailto:RoboMan91324 at aol.com] 
Sent: September  23, 2015 3:26 PM
To: bgilbert at gilberts-bc.ca;  virtualvairs at corvair.org
Subject: Re: Running an engine without  shrouds

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_ (mailto: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)  
[mailto:RoboMan91324 at aol.com]  
Sent: September 23, 2015 10:11 AM
To: _virtualvairs at corvair.org_ (mailto:virtualvairs at corvair.org) ; 
_bgilbert at gilberts-bc.ca_ (mailto: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

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