So, my original question was going to be how an internal combustion engines always spin in the correct direction. I figured that one out (the starter spins in it in the proper direction to begin with, and it runs on from there).
Then I got to thinking a little more - if I spin the engine backwards (maybe wiring the starter backwards?), would the forward gears now run the car in reverse? Meaning I’d have 4-5 reverse gears and one very low forward gear?
A four-cycle engine requires a new camshaft to run backwards, because the intake would become the exhaust if you just spin the engine backwards.
There used to be kits to put Corvair engines in Volkswagens, but the engines didn’t spin the same direction. On earlier VWs, the ring gear in the transaxle could be flipped to get the car to go with four forward and one reverse gear, but it caused the ring gear to run backwards from the way it was supposed to run. The good kit included a camshaft for the Corvair engine so it would run in the VW direction.
no. all car engines nowadays are 4-stroke cycle, and they will not run in the “reverse” direction unless you change the camshaft and ignition timing.
now, with 2-stroke cycle engines, some types (reed-valve, side-ported) will run equally well in either direction. Other types (rotor intake) will run great in one direction but only marginally in the other direction. a different type (blower-scavenged, closed crankcase) will run either direction if you change parts around (e.g. the older Detroit Diesels.)
According to an old car talk puzzler, this was true of the original 2-stroke Saabs, but was probably true for many other 2-stroke cars.
Another use for custom cams that make 4-stroke engines run in reverse is for twin-engine boats where you want two identical more or less off-the-shelf car engines, but want the screws turning in opposite directions.
One car that could be run in reverse was the “Frisky” (I’m not making the name up!) - my great uncle has one that he was given by the manufacturer in I would think the fifties or sixties. My mother learned the basics of driving on it when she was around five or six.
Also, semi-related to the OP, another person in my family has a Locost (effectively a home built Lotus 7) where the gear box is from a motorbike. If you’re not aware, motorbike gears don’t have reverse so while I’m not certain exactly how the car is setup somewhere there is a reverse gear in the drivetrain, separate from teh gear box, that effectively means the car has six reverse gears and can certainly hit three figures in reverse if called upon to do so!
Some older engines (mostly diesels probably) could be lugged down too slow, nearly stall, and then start running backwards. You’d end up with six reverse gears and one forward. Breathing through the exhaust and blowing out the air cleaner1
Was actually a common story with some early two cylinder John Deere diesels. They later redesigned the camshaft to keep that from happening.
If I remember correctly, the early to mid 1970s Yamaha 200 motorcycle (2-stroke engine) would occasionally get spun by the starter in reverse, and the porting was such that the engine would run backwards. You always wanted to let the clutch out easy and check how the bike wanted to move before taking off, just in case the engine was running backwards.
Flipping a leaf-sprung rear end on say, a '60s Ford Falcon or similar car wouldn’t be too hard. You’d have to have spring perches and shock attachment points cut off, moved, and rewelded. You might have to rerun some brake line. Bleeding the brakes would be a bitch after, however. The bleeder screws would now be on the bottom of the cylinders so you’d have to flip the car over so the air in the cylinders would be at the top. The gears in the diff would still be running the right way.
Did this in a couple mid 70’s full size Chevy demo derby cars. Besides rewelding all the attach points, you also have to reverse the brakes so the automatic adjusters don’t over tighten the brake shoes. It’s strange driving a car capable of 100 mph in reverse but has a max speed of about 20 going forward.