<VV> Running an engine without shrouds

Thu Sep 24 11:11:01 EDT 2015

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

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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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