Originally Posted by
reddog3
I understand the "gibberish" part- no offense taken. I'm not an ME either, therefore might have a problem being understood. It's a bit difficult to explain in text , and maybe even harder to understand. Let's try a different approach.
If you follow "instructions" and seat both bearings into the shell... all is well until you push the spindle into the bearings. Since the spindle is an interference fit in the inner race, the bearings will be sideloaded (for lack of a better term) whether you push, or pull the spindle through.
If you support the inner race with your puller it pulls into the inner race only. If you follow "directions" you push, or pull the spindle in, but the bearing is only supported on the outer race in the shell. All the stress is on the balls. Once in place following "directions" there's no good way for correction to center the bearing. Same way for installation of the NDS. If you followed "directions" the NDS bearing would already be in place. Driving the spindle in would stress bearings on both sides.
I push the NDS bearing in after the crank spindle is set in the DS. Here's a part that may be tough to understand (as per your question.) I support both races because there's an interference fit on both the inner and outer races. To use one race or the other to seat the bearing would side- load the balls. As mentioned, the puller is supported on the outside of the DS spindle. Not doing so would sideload the DS bearing so one could pull in the other side. Doing do allows the DS bearing to float free, rather than using the shell to support the puller. Still clear as mud?
Problem is, well not really, you have to fashion your own puller set. If you do enough BB30/PF30 work, and you want them to run free, it's no biggee- about an hours worth of lathe time.
Nope...what you write, just isn't so. Oh you can do it your way which you probably have but there is no value added and in fact maybe worse. Pressing both bearings in place first and then installing the crank spindle is industry practice and a sound approach.
First there is no interference fit between spindle and ID of inner race...it is a slip fit with angular tolerance. Btw, I am a ME.
BB30 bore to bore cylindricity for all top frame makers in the industry accounts for outer to inner race bearing tolerance that allows for a tolerance of lack of co-axiality. So precise alignment or sharing the same axial centerline of both bearings isn't essential. Of course it needs to be close and most top frames are.
A little know fact among I would say most that think they know bicycles is....an English threaded BB will have greater axial bearing mismatch bearing to bearing centerline compared to BB30. This for example is one of the benefits of BB30, better agreement of bearing position side to side for lowest possible rotational friction.
As far as pressing in bearings goes...always press them in with pressure on the outer race. This is the ONLY way to do it to ensure the bearings aren't spoiled. Trying to press on both inner and outer races concurrently will create more harm than good. because any side load on the inner race with restraint to the outer race can damage the balls or races.
The biggest mistakes that techs make when installing BB30 are:
1. BB30 bores and bearing outer races aren't perfectly clean.
2. Loctite isn't used or wrong spec Loctite is used.
3. Bearings aren't pressed in absolutely straight aka orthogonal to bores which ensure proper bearing centerline agreement and seated fully to mating snap rings.
4. Crank preload is set wrong...either too loose aka play or too tight which will increase spindle drag and induce premature bearing wear. For wave washer cranks which account for a large percentage, the wave washer should be compressed to approx. 1/2 of its free standing height. This take careful selection of spacers based upon BB shell size/tolerance.
You don't have to or more importantly, you shouldn't use the spindle as a mandrel to promote alignment between bores as you propose.