If the new engine is identical to the old, I don't see a problem. If you are going with a more powerful engine, the old transmission might not have strong enough internal parts to hold up, and you could blow out your transmission.

But you old transmission won't hurt your new engine.

Won't bother it. If old engine was shot, the new engine might have enough more power to quicken the demise of a worn transmission. But a worn transmission won't hurt a new motor.

Car parts age together. Put a new engine in the vehicle and with the more power and torque it could affect all of the drive components. You best ask a mechanic, a professional, for advise.

Put that new engine in and replace the trans whenever you are ready. Be sure to unbolt the torque converter before pulling the engine.

Could not fit right

I want to put a new engine in my Ram 1500 2001. But i dont want to put a new transmission in right now. (In a month or 2) I'm wondering if my old transmission might mess up my new engine some how if yes how?