AMD has had to reposition the usual AM3 mounting holes, so while our Asus Crosshair VI Hero test board included the usual plastic cooler mounting arms, if your cooler requires a backplate with threaded holes, as do most AMD socket coolers, especially AIO liquid coolers, then you'll need to purchase/obtain a new backplate with the correct mounting hole spacing.
Click to enlarge - AM4 vs previous AMD backplate
One way round this is if, like us, you have a spare old AMD board and the Ryzen-capable board you want to use has both sets of mounting holes like our Crosshair VI Hero does i.e. both AM3+ and AM4 mounting holes.
Click to enlarge - AM4 backplate in AM4 mounting holes (left); AM3 backplate in an AM4 motherboard, which works fine (right)
AMD backplates are also readily available on well-known auction sites. This way, you can use the standard AMD mounting screws, ensuring any mounting plates will line up with the standard backplate too. The most likely course for transplanting an old or AM4-incompatible cooler is to reach out to the manufacturer. Some are offering free adaptors, while some like Corsair are demanding a small fee.
Click to enlarge
We tried an AM3+ backplate on the Crosshair VI Hero and were able to successfully fit an NZXT Kraken X42 cooler using the normal AM3+ mounting gear. The standard plastic socket mounts are back as standard, which is why some coolers are already listed as being compatible with AM4.
This obviously won't be the case with anything that uses a proprietary backplate, such as that for EKWB's waterblocks and Predator AIO liquid coolers. Here's its replacement backplate that's AM4-compatible, with instructions here and Predator owners should see the EK-XLC Predator AMD AM4 upgrade kit.
The Ryzen 7 1800X and 1700X are slated not to come equipped with a cooler - AMD told us this last week. However, there is a trio of new top-down coolers available, but these will either come with later Ryzen models that haven't been confirmed or only available through system integrators in pre- or custom-built systems. There's the Wraith Max, Wraith Spire, and Wraith Stealth - the latter likely to be included with the lower-wattage 65W parts, while the Max and Spire will feature RGB ring lighting.