[Closed] Boardman BB30 bearing tip

Hello,

This post is only intended to help people with a little information. It is totally up to you if you believe it or not. Very few special tools needed.

About 4 months ago I bought a Boardman MTB Pro. I knew at the time some people have had problems with the BB30, even to the point of having bikes replaced by Halfords and the problem comes back !

At the 400 mile point, my BB became tighter (more than it was when new) and the bearings became notchy. I have a basic engineering and mechanical background, so with a little web searching and fiddling, I found the problem with my BB30. Basically the BB has been machined too tight for the bearing. A standard bearing fit for this sized bearing, as stated by bearing manufacturers, is about 12 microns, my Boardman is 50 microns! This is too tight for the bearings and is causing the stiff and notchy crank.

So here is my fix that will be carried out in the next few days when the bearings and tools come in.

PLEASE NOTE, I HAVE NOT DONE THE WORK ON MY BIKE YET AND IF YOU DO WHAT I AM INTENDING, YOU WILL LOSE YOUR WARRANTY. YOU DO THIS JOB AT YOUR OWN RISK !!

OK, now that's out the way.

First fit a 10mm allen key into the non driven side of the FSA Comet crank and undo the bolt in the normal anti clockwise direction. Ignore the outer retaining nut that has holes in it. As somebody that has never seen this type of self extraction crank, this outer ring is just a retaining nut that gives the 10mm crank bolt something to push against for the self extracting crank action. As you undo the 10mm allen key, you will find that the crank is automatically pulled off its shaft splines.

Once the crank is removed, you need to drift the shaft out of the bearings. I found that a rubber 'dead blow hammer' was not enough. I placed a brass block onto the shaft and gave the shaft a few swift blows with a normal steel hammer. The bearing fitment onto the shaft was very tight on my bike, so required this extra force.

Once the shaft is removed with the driven crank attached, you will find that the bearings still feel notchy giving the impression of bad bearings.

The bearings at this point now need removing. I used a short length of 10mm steel bar with the end edges ground off so it was smooth and would not damage the bearing seats. You will need to give the bearings a few swift blows at about four points to move it away from the cir-clip. Once the bearing is off the cir-clip, you will be able to remove the cir-clip from it's groove easily. It is very soft so I don't think you would need the proper cir-clip pliers, maybe just two very small flat end screw drivers? I used an old pair of long nose pliers that I ground the tips to points. The cir-clips will not come out the BB at this point as the bearings stop them. This does not matter as all you are trying to do is get access to all sides of the bearings so they can be GENTLY drifted out with the smooth ended bar and hammer. Make SURE you hit the bearing on all side EVENLY until the bearings fall out.

You may well now find the bearings 'seem' perfect and not notchy at all. If you clean the outer race of the bearing and BB bearing seats and measure them with an ACCURATE digital vernier gauge, you should find the bearing seats are about 0.002" smaller than the outer race of the bearings. That is your problem and no amount of bearing replacement, Halfords queueing or even whole bike replacements will fix this (assuming all the Boardman bike frames are machined the same).

What you now need to do is buy a small bore cylinder honing tool like the 'Draper brake cylinder hone 25mm - 57mm honing tool 56244'. These can be bought for under £10 from 'that' auction site! You will also need to buy two new bearings, part number 6806-2RS. I am told that some bearing manufactures call them 6106-2RS (don't know why) The size of the bearings are 42mm x 30mm x 7mm and have two rubber seals (2RS). I have bought SKF bearings at £18.50 each from my local bearing specialist, but much cheaper bearings can be bought from 'that' auction site for as little as £2 each! (but the cheaper ones will be of a lower quality).

With the bearings and cir-clips now removed, you must clean the bearing seats with a cloth and hone the seats with the honing tool. THIS WILL VOID YOUR WARRANTY! Fit the honing tool into a drill set to a slow speed. Lubricate one bearing seat with light oil, like WD-40. Compress the honing tool stones and put the tool into the BB making sure the stones are fully flat within the bore. Now simply start the drill and VERY GENTLY move the honing tool back and forth while turning to remove material from the bearing seat. Make sure you keep the stones lubricated and do not move the tool back and for too much. You must keep the stones nice and flat on the bearing seat. Periodically remove the tool, clean the oil off and measure the bearing seat.

You are looking for a -12 micron bore (0.0005"). That is to say the BB bearing seat needs to be 12 microns (1/2 a thou) SMALLER than the external diameter of the bearing you have. You will need a digital calliper to measure this.

Once you have honed the bearing seats to the correct size, you can clean the bearing seats and cir-clips with meths or other cleaner that will not leave an oil residue. Refit the cir-clips. Remove the rubber seals from the bearings and pack the bearings with a thick sticky grease and refit the seals. Clean the outside of the bearings with the cleaner you used for the seats and cir-clips.

You now need to refit the bearings. You will need to use a bearing retaining compound like 'Locktite 641'. This is a medium strength retainer that will allow for disassembly. USING A RETAINING COMPOUND ON THE BEARINGS WILL VOID YOUR WARRANTY!

you will now find that the refitting of the bearings will not need any special tools. Just make SURE you tap the bearing home gently, making sure you use ALL sides of the bearing evenly. DO NOT HIT THE INNER RACE! or scratch the bearing seat. Wipe off the excess bearing retainer and allow the retainer to dry according to the brand you have.

Then simply push the driven crank shaft and its spacers back through the bearings until fully home. You may find that the crank shaft is a little tight. Do not force it in, simply polish it with 800 grit wet and dry paper (used wet) until the crank is a nice snug fit in the bearings. It may be a good idea to test fit the crank on the new bearings before fitting the bearings? It must not be loose and do not use retaining compound on the shaft. Then wind on the 'pre-tension' nut onto the back of the non driven crank, refit the alloy spacer making sure it is the right way around. Push the non driven crank onto its splines and do up the 10mm allen key bolt to a tension of 40 foot pounds. If you don't have a torque wrench, 40 foot pounds would be quite hand tight with a long (6" or 150mm) allen key.

Job done.

ALL THE ABOVE WORK WILL VOID YOUR WARRANTY AND IT IS ONLY MY OPINION, AT YOUR OWN RISK.