Engines running "backwards"


My Son asked me this morning . . . and I can’t answer . . . why do Honda engines rotate in the reverse of most, and do any others? Rocketman


Lets see pistons go up and down or down and up, how do they run backwards???


Most FWD cars have the engine on the passenger side and the clutch/transmission on the driver side. This means the engine runs in the “normal” direction. Hondas tend to reverse that and that means the engine has to run in the opposite direction. The crankshaft turns the same direction but the power is taken off of the other end of the engine on Hondas.

On the older air cooled single overhead cam Honda four cylinder motorcycles, the power was taken off the center of the crank so that the right half of the engine ran standard rotation but the left half of the engine turned backwards. Yet, it was a one piece crankshaft so in reference to the rider, the entire crank turned forwards (same direction that the wheels turned).

Old two cylinder John Deere tractors also turned reverse rotation because the clutch/power takeoff was on the right side of the tractor.


Rocketman is referring to the direction of engine crankshaft rotation, if I have it the right way round the majority of engines are left hand or counterclockwise rotation. Honda engines are right hand or clockwise rotoation ~ though even that isn’t consistent.

BTW - Engine rotation is at the flywheel or output end, not the front pulley.


“Why do Honda engines rotate in the reverse of most?” was my question, not the movement of the pistons. I was referring to the rotation of the crankshaft. Rocketman


That one was easy, wasn’t it? A little more difficult one would be, “Why do (did) some distributors turn clockwise, and some counter-clockwise?”


well, maybe location,gear tooth cut,again location. and so on ,you can make and design anything, to turn in the intended direction,you so choose. not difficult.

hope that helps


Some tractor pull vehicles have two or more, otherwise identical, engines that run in opposite directions and are linked by a crossbox.


Yeah, and now you’ve got me going, I didn’t know the answer but natural curiousity caused me to Google to virtual blindness. Not a single reference…gah !

Maybe an email to Honda will uncover the answer, I’m sure they didn’t do it because they thought it was a good idea. Though it might be an evolutionary extension of their motorcycle engines which also turn backwards.


I think that Rolls Royce Merlin engines used in North American P-51 Mustangs as well as in Supermarine Spitfires turned reverse and a gear reduction unit made the prop turn normal rotation.

Home built airplanes that use air cooled Volkswagon engines need props pitched for reverse rotation because the bell housing is used as an engine mount on the firewall and the prop is attached to the end of the engine that normally holds the fan belt pulley.


FWIW, several vintage engines would get out of tune and run backwards with no damage.


I remember an outboard motor–I think it was a Neptune–that would run either direction. This was a 2 cycle, one cylinder engine and to back out of the dock, one put the starter rope in the notch and turned the flywheel in one direction. To go the other way, the other notch on the flywheel was used and the flywheel was turned in the other direction. If one shut the motor off and as it kicked back hit the throttle again, the boat motor would run in the opposite direction without being restarted.

It also seems to me that Chevrolet made a V-8 marine engine and the crankshaft turned the opposite direction of the automobile V-8 engine. I think I remember reading about a person using this engine to convert a Chevrolet Corvair to a V-8. The crankshaft had to turn in the opposite direction from a regular Chevrolet V-8 for this installation.


I have seen diesel boat motors start backwards. Then you see everyone freak out and shut everything down as it is sucking water into the exhaust.


Kids ask the darndest things . . . I usually make something up . . . but this kinda got me curious too. There has got to be a reason beyond “we just want to do it”. I’ll keep looking and let you know if I find out. Rocketman


That’s probably a Detroit, It happens with trucks too. Really funky having 13 reverse gears and 1 forward.



I’m pretty sure GM 350 V8s can be set up to turn either direction, and the marine version is often reversed on one of 2 engines in a boat. One prop goes clockwise and the other counter-clockwise. This keeps the high torque from rocking the boat when you really hit the throttles.

If you think about it, if the cams have symmetric lobes, you would not have to change much to get any engine to run backwards. The distributor and the oil pump might have to be changed, maybe reroute the belts, but nothing major.


This was an excellent opportunity to explain that there is no “backwards”. It is merely a perception with no basis in physics.

You can always tell a French helicopter 'cause their main rotors turn opposite everybody elses.


Hi MB . . . that’s why I put “backwards” in quotation marks . . . what is frontwards anyway? I suppose my English professor friend might have corrected me to say . . . “opposite the majority of many late model engines”. Rocketman


Yes, but how did you explain it to your son?

An optimist says the glass is half full.
A pessimist says the glass is half empty.
An engineer says the glass is the wrong size.

It’s all a matter of perspective.


You would still need a camshaft ground for reverse rotation. On a dual overhead cam engine, it may be possible to rephase the cams for reverse rotation.

There was a radio control model airplane four stroke engine a while back that you reversed simply by interchanging the exhaust pipe and the carburettor. The intake and exhaust valves on this engine were identical. I suppose that could be done on an auto engine but exhaust valves tend to be smaller than intake valves and I’m sure the performance would suffer if they were used as intake valves and the intakes were used as exhaust valves.