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Old 12-08-2005, 05:07 PM   #1
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Default Engine Rotation Direction

Hey everybody, one of my first posts so bear with me and I think I've got it in the right section.

I'm curious which way the engine rotates, when viewed from the flywheel to the harmonic balancer, rear to front? I believe it rotates counter-clockwise, ccw. Do all engines rotate in the same direction? Are they all ccw? I've heard some imports and boat motors go cw, but I'm asking for in general American motors, small-blocks, ls1/2/6,etc.

Here's a little of why I'm thinking:
If you view the car moving forward from the left hand (driver) side, the wheel rotates ccw. This means the axle when viewed from the drivers' side rotates ccw. If you look at the driveshaft from rear-front, it will be moving ccw also. Then at the transmission, the gear will be moving ccw as well. This means the countergear will move cw, the input gear ccw, and the flywheel/crank ccw. I'm basing my views on either rear->front or on the drivers' side.

Is this correct? Does the crank move ccw?

The reason I'm asking is because in Fred Puhn's How to Make your Car Handle, he has a picture showing an axle torque going ccw and unloading the rear right wheel and loading the left rear. The explanation is that that is why the right rear breaks loose first when you gas it. I'm fine with that, but he also shows the engine torque as going cw. But if the motor goes ccw, why does he show it as going cw?
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Old 12-08-2005, 05:21 PM   #2
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um....im confused but in short, when viewing the motor from the FRONT of the car, the motor rotates clockwise. When viewed from the back, it rotates counter clockwise. By any chance, would you happen to have that picture you speak of?? I'd like to check it out.

Edit - I see what you're saying now....I would believe that it does rotate ccw.
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Old 12-08-2005, 05:52 PM   #3
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Quote:
The explanation is that that is why the right rear breaks loose first when you gas it. I'm fine with that, but he also shows the engine torque as going cw. But if the motor goes ccw, why does he show it as going cw?
Whichever way the crank turns, you are going to "torque" the chassis the other way.

It's the old "for every action there is an equal and opposite reaction" situation.
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Old 12-08-2005, 06:24 PM   #4
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I recall reading about an old circle track trick where the engine rotation would be changed on some tracks for chassis torque. I can’t remember the details of why they did this, or what they did to the drive train to convert the rotation. Interesting to think about this though.
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Old 12-08-2005, 07:05 PM   #5
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mdrew,

I have the answer, but I'll give you guys a few hints. I was pretty floored
when I read this...some things you just never think about!

RE: Engine rotation

Why would running NASCAR in the opposite direction on a high bank oval
cause potentially dangerous conditions?

The clue is touched upon in "NO-Option-2002"'s post.
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Old 12-08-2005, 08:12 PM   #6
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It unloads the outside front tire? Gyroscopic effects?
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Old 12-09-2005, 08:09 AM   #7
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You could open the hood with the engine running and look at the belts or pulleys to determine engine rotation direction.

NO-OPTION-2002 is correct about torque reaction. With a longitudinal engine like a Camaro, if you rev the engine in neutral the left front fender raises. That is the reaction to engine torque produced in the opposite direction.

To quote Dave Segal, of Milliken Reasearch Associates: (emphasis added)

"Conventional front-engine, rear-wheel-drive cars with live axles are subject to wheel load changes due to drive torque. This is most apparent when accelerating hard in a low gear. With a conventional counterclockwise-turning driveshaft (as viewed from the rear), no special torque reaction members in the suspension and an open differential, the right rear tire spins first.

The problem occurs because the driveshaft torque must be reacted by a change in rear axle wheel loads with the left rear increasing and the right rear decreasing. However, solving for the changes in wheel load is compounded by the fact that the driveshaft torque must also be reacted by the chassis through the engine mounts. This requires that a moment reacting the driveshaft torque be produced at the front of the car due to chassis roll."


On a CCW (left turns) oval track, engine torque reaction raises the left front and therefore loads the right front (outside) tire under acceleration. That's just the opposite of what you'd like to happen. Some sprint cars may use reverse rotation engines which plant the inside tire and may even raise the outside tire if torque and bite are high enough.

Smokey Yunick ran some reverse rotation engines (Hudson's, I believe) early in NASCAR racing before that was outlawed. Reverse rotation would certainly help unload the highly loaded outside tire on a banked track, so you would have to readjust the suspension loading. For a couple of reasons including engine rotation direction and right side weight bias on road courses, which are predominately RIGHT, Nextel Cup cars unload the left front enough in left turns to carry it after it clips a 2 inch high curb.

Quote:
Originally Posted by Adrenaline_Z

RE: Engine rotation

Why would running NASCAR in the opposite direction on a high bank oval
cause potentially dangerous conditions?
Ah, the dreaded Coriolis Effect.
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Last edited by Old SStroker; 12-09-2005 at 11:22 AM..
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Old 12-09-2005, 11:22 AM   #8
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Z-

What Mr. SStroker said……other than that, I’m not coming up with anything. But I haven’t had my caffeine yet either. I don’t function well prior to sugar and caffeine…

SStroker-

It was Smokey. I can’t believe I forgot where I heard it. Do you recall what he did to the drive train for the reverse rotation? Damn that guy was smart, and way ahead of his time…..
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Old 12-09-2005, 11:25 AM   #9
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Quote:
Originally Posted by mdrew
Z-

What Mr. SStroker said……other than that, I’m not coming up with anything. But I haven’t had my caffeine yet either. I don’t function well prior to sugar and caffeine…

SStroker-

It was Smokey. I can’t believe I forgot where I heard it. Do you recall what he did to the drive train for the reverse rotation? Damn that guy was smart, and way ahead of his time…..
Smokey flipped the rear axle upside down. Drive shaft was a little high, but some floorpan surgery fixed that. He was especially way ahead of the inspectors.
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Old 12-09-2005, 11:33 AM   #10
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Marine reverse rotation engines are available
(twin inboards, you want one of the props to
spin opposite the other so the back end doesn't
want to skate to the right by paddlewheel
action).

I know they have a reverse cam, swap the plug
wires around on the distributor, don't know about
the water pump & oil pump. But that ought to be
about it, for a marine reverse SBC/BBC like what
I am talking about.

There were some cars like old Volvos that were
"reverse" all the way back to the diff, the pinion
was I think above instead of below the axle line.
That would be some work, to do at a high power
level (not Volvo 4-cyl power). Wonder if you can
put the center section upside down and the gears
in backwards on a Ford 9"?
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Old 12-09-2005, 11:46 AM   #11
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Yeah, you can't argue with the SSTroker boys.

Jon is pretty much on the ball again!
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Old 12-09-2005, 11:53 AM   #12
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Quote:
Originally Posted by Adrenaline_Z
Yeah, you can't argue with the SSTroker boys.

Jon is pretty much on the ball again!
I was kidding on the Coriolis bit. Depending on the latitude and vehicle speed it amounts to maybe .001 g. Even "Smoke" might not be able to feel that.

Of course just reversing track direction without moving to RH drive would probably require flush race seats.
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Old 12-09-2005, 01:38 PM   #13
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Quote:
I was kidding on the Coriolis bit.
As long as you don't tell me water will drain in the opposite direction according
to your position from the equator, I'll forgive you. :-)
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Old 12-09-2005, 02:31 PM   #14
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Red face

I was just reading this and thought "bet its outlawed from NASCAR because of Smokey."

go figure
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Old 12-09-2005, 03:00 PM   #15
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off topic...

There are/were two stroke diesel engines that could reverse direction by starting them backwards. They basically ran either way.
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Old 12-09-2005, 03:18 PM   #16
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Quote:
Originally Posted by Adrenaline_Z
As long as you don't tell me water will drain in the opposite direction according
to your position from the equator, I'll forgive you. :-)
It's a tough experiment to control, and the container you are draining needs to be very large and very accurately made, but I believe, given those conditions, water will drain CW in the northern hemisphere. But wait, there's more: why do hurricanes rotate CCW in the Northern hemisphere? I used to think it was because they were female, or named aftrer females who are often contrary, but even when given male names, or Greek letter names, they continue to spin CCW. Another theory blown away, right? Or is Coriolis still applicable? How?

On topic: My take on engine rotation is because it's easier for a right handed person to crank start CW rotation (viewed from front). Right-handed early vehicle engine designers probably outnumbered the southpaws.

Ever notice than many older European aircraft engines spin their props the opposite way from those originating here in the Colonies?
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Old 12-09-2005, 03:29 PM   #17
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I need to say a big thank you to everyone for replying so well and quickly. You guys have cleared some up, but I still have one question: If the crank & driveshaft both move ccw when viewed rear->front, why do their torque reactions go the opposite way. Up front, the chassis responds to the force put into it by lifting the left and planting the right, but in the back the axle responds to the force put into it by lifting the right and planting the left. The forces are rotating in the same directions and planting opposite sides!
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Old 12-09-2005, 03:38 PM   #18
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Quote:
Originally Posted by Adnectere
I need to say a big thank you to everyone for replying so well and quickly. You guys have cleared some up, but I still have one question: If the crank & driveshaft both move ccw when viewed rear->front, why do their torque reactions go the opposite way. Up front, the chassis responds to the force put into it by lifting the left and planting the right, but in the back the axle responds to the force put into it by lifting the right and planting the left. The forces are rotating in the same directions and planting opposite sides!
Seems logical. Lift front left = down rear right
Every action has an equal an opposite reaction. So sum of the forces = zero. But, you can't add forces where ever you'd like to. sum of the moments have to equal zero too. (unless it is motion)
Quote:
Originally Posted by Old SStroker
On topic: My take on engine rotation is because it's easier for a right handed person to crank start CW rotation (viewed from front). Right-handed early vehicle engine designers probably outnumbered the southpaws.

Ever notice than many older European aircraft engines spin their props the opposite way from those originating here in the Colonies?
showing your age in this post
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Old 12-09-2005, 03:48 PM   #19
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If you think of the rear wheels' rotation being resisted by the vehicle's inertia, effectively locking them, then a live rear axle assembly will try to rotate as a unit in concert with the driveshaft, thus lifting the right wheel/compressing the right side spring.
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Old 12-09-2005, 03:51 PM   #20
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Good replies again. OldSStroker, that's very insightful about the hand-cranking. I like that explanation, it makes good sense.

Maybe you're (Treyz28) right about the sum of the forces. I was thinking of two individual forces:#1 the torque on the engine mounts and the chassis lifting up front and then #2 the driveshaft's torque on the axle in the rear. Maybe they're both just part of the same sum. That makes pretty good sense when I think about it holistically.

Something in my brain isn't clicking though. -Lashes the gerbils to run faster- If the chassis up front responding is because of the engine mounts being torqued, then that opposite/equal/reaction should finish there. There isn't torque through the engine mounts being applied to the axle.

The transmission mounts have no torque because of the driveshaft? It doesn't move? Or is it just stuck via the flywheel to the motor so tight that they move together and the force goes through the engine mounts (but not the tranny mounts?)?

I need stronger gerbils or a larger diameter wheel for them to run in.
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Old 12-09-2005, 03:51 PM
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