i have a 2005 pt cruiser that had a new engine recently put in. its only got 50,000 miles on engine and body. so now the car makes a loud knock noise when i hit bumps or take turns. it comes from the front end. i have replaced the engine mounts and that didnt fix it, i also checked the wheel bearings and those seemed ok. the knock sounds heavy. does anyone know what it could possibly be please?

Might be an upper strut mount/bushing. Might be a ball joint. Might also be a sway bar end link, although that usually makes a smaller clicking sound rather than a big clunk. Might just need an alignment. Most likely suspension related.

A few things you can try:
Grab the front or back of either front tire and try to rock it back and forth. If it doesn't go anywhere, you can probably rule out ball joints as the culprit. Try it on both tires. If there's play or "floppiness" in either wheel, you may have a bad ball joint, or a bad pushing on one of your control arms. A lot of times if you have a bad control arm bushing you'll also experience feedback through the steering wheel along with the clunk. Control arms on FWD cars like the PT cruiser aren't bad to replace at all, definitely driveway repair material.

You can also have someone bounce the front end of the car up and down while you try to pinpoint the source of the sound by ear. Don't get your head smashed. Listen specifically at the upper strut bushing, and down near the hub. If you think you've found the general area, start feeling parts to see if any of them are moving in sync with the clunk. You can feel a sway bar end link click, for instance, and you can definitely feel a control arm clunk.

Don't PT Cruisers have suspension issues...quite common.

IIRC, they used the same struts from a Neon and threw them on the PT Cruisers.