RX7Club.com - Mazda RX7 Forum - quick ? will a manual engine and auto

It totally depends on the engine!

Obviously, manual transmissions have flywheels, while automatics have flexplates (the torque converter acts as a flywheel). However, the transmission in both cases will pilot into the back of the crankshaft. On Mazdas, the torque converter pilot uses the same hole that the transmission input shaft pilots into, so there is no problem.

However, on many cars, the torque converter pilots into a fairly large hole in the back of the crank, while the pilot bearing for the manual trans goes into a second, smaller, deeper hole. In many cases (mainly American cars from the late 60's and 70's, some 80's) engines destined for automatics may not have the hole drilled for the manual trans's pilot bushing. That is where you run into trouble and need to remove the crankshaft and have the new hole drilled (it is NOT something you can do with a hand drill!).

And then there are other weirdball things, like many Toyotas and Mitsubishis (and Saturns!) that do not even have pilot bushings at all, they just trust that the input shaft is going to be concentric with the crank! And Neons (and maybe others?) that have done away with flywheels on manual trans cars. (Huh?) They use a "modular" clutch assembly that is flywheel, pressure plate, and clutch disc all rolled into one, and it bolts to a flexplate just like a torque converter. Actually more convenient this way, since you don't have to worry about the finish on the flywheel when you replace the clutch, since it is getting replaced all in one shebang.

If it's for a rotary, these are kind of a special case, since the flywheel is kinda part of the crank assembly, so you need to get the correct flywheel to fit the *engine*. Thus if you are thinking of getting an automatic engine for your FD, you need to ensure it's an FD engine (no-brainer) and use your existing flywheel. If possible, this would be a great opportunity to put a lightweight flywheel in, because it bolts on to the rear counterweight from an automatic car.