I’ve broken down this fork setup into cleaning/preparation and installation. If your forks are sticking and you need to just get that resolved jump down to the installation. If your forks are blasted with dirt after some initial runs, then start from the top. These steps were submitted by Chris Haertel who has a ton of experience with both the VMX450 and the new MM450 bikes by Atomik. Thanks again Chris!
4. Slide off the seals, bushes and cap keeping in order and checking to make sure everything is as it should be according to the instructions. Make sure part no 0446A and 0447C are installed correctly. One of mine was upside down. Photo 5
5. (OPTIONAL, but it helps!) Polish the shafts until mirror finish. I have a bench grinder with a big polishing wheel, does it quick and easy.
10. Pour some oil into the tube and start to work the shaft. Push the shaft all the way in and fill with oil. Work the shaft to bleed the air and repeat filling ( always filling to the top with the shaft compressed ) until all the air has gone. Pull the shaft out and fit the spring and the top cap. Photo 10
11. Pushing the fork up and down on the bench should feel smooth with no sticking. Start tightening the lower cap until you can feel resistance in the shaft and back off slightly from there. All good if you can tighten it fully. Five to ten runs on a track jumping will bed them in and you’ll be able to fully tighten them. Give them a wash down with some detergent and dry off. It’s normal for them to weep slightly to start with, just wipe with a cloth, as they bed in this improves. Keep them clean wiping them over and they will last a long time. Change the oil often will help as the bodies aren’t hard anodized and will wear. Hope that’s some help. You don’t have to do the polishing but it does make them slide better. I use 40 wt in mine to start with. Maybe try 30 and work up if required as I hammer mine pretty hard.
Next assemble the forks into the clamps tightening only the top two screws. Next with the front wheel in place push the front end through its full travel and release several times. There should be no sticking. Tighten the lower triple. clamp screws lightly and check again for binding. Nip up don’t over tighten. Next I tighten only one axle clamp screw. I don’t blueprint my forks as I find the above method works well without resorting to sandpaper. The forks are usually bedded in after a several runs I find. Oh and with the sticky forks after a big crash ( rarely happens they are just tweaked in the clamps ) this is what I do with the lower screws on the triple clamps and even one axle clamp screw loose push the forks through their range several times, they should feel smooth with no sticking. I then nip up the lower triple clamp bolts and try again.
If the forks start to bind I usually just back the lower bolts ofF 1/4 turn. I always leave one lower axle clamp loose as well. This gives me forks that work well, are ultra smooth, last a long time between seal changes and never stick . I change the oil every 5 to 10 hrs use depending on running conditions. About every 40 hours or when the forks start to leak or develop excessive slop I change the pistons, seals, and bushings and if the shafts look good re polish and reassemble. Try 60 wt oil at this point. I find it best almost always once the forks have some time on them.
(NOTE: Atomik sells an Option Front Axle Set for MM450 and VMX450. “The Option Front Axle uses two end bolts that capture the fork dropouts and prevents the front forks from wanting to spread…which can lead to binding in the front suspension and decreased performance.”)