Hot take: I don’t always remove and replace sealed bearings during an overhaul.
“A bearing is only as good as its mount.” I learned this at UBI in 1997. We were learning about chasing and facing and frame prep and it has stuck with me ever since. This was taught in reference to bottom bracket and headsets and making sure the frame surfaces were clean, parallel and met the correct specifications. It ensures there’s no misalignment and that the bearings can be properly tensioned with no tight spots due to races being out of phase. This also applies to a bearing bore for a sealed bearing.
For example, in overhauling a hub, the bearing bore is machined to a specific tolerance for an interference fit. Not only can this fit can be damaged if the bearing is not removed cleanly, but also just from repeated removal. Damage or wear can create a loose fit that will eventually result in the hub or part needing to be replaced. Most sealed bearings can be flushed and re-lubricated, extending the life of the bearing. The time to replace a bearing? If it has developed play. Pretty simple, right? (After some long-winded technical talk, of course).
So, when I overhaul any hub, BB or headset with sealed bearings, I don’t always pull and replace the bearings. First I check for play in the bearing. If there is none then I remove the seals and flush the bearings and re-lube. Done carefully, this process will not damage the seal and will extend the life of the bearing and component in which it’s housed. I also look for any evidence the bearing is seized. Corrosion around the seat and on the axle will indicate this. If there is corrosion, cleaning and removing the bearings will ensure there is no damage behind them.
When it comes to replacement, I avoid a slide hammer if at all possible. There are techniques to help remove a sealed bearing cleanly using a slide hammer but you can’t always use them appropriately on a bike. It is very easy to get off line with a slide hammer and pull the bearing out at an angle which will cause damage. Additionally, the expanding collets used with slide hammers have a lip designed to get behind the bearing and there’s not always clearance for this. Forcing them into the part can cause serious damage. I prefer a press and drift method for removal. This ensures the bearing is being pushed from the seat in line with the bore.
Sealed bearings can be overhauled and serviced without unnecessary removal. It should be assessed on a case by case basis. Yes, removal and replacement is often faster, but with the possibility of damage it’s a worthwhile trade off to be a little more thoughtful in the process. Thanks for letting me nerd out on this one! Let me know your take, or if there’s anything you’d like me to deep dive into next.