This is definitely not manufacturer approved! The bearing cups on a Shimano XT Hollowtech II bottom bracket have "DO NOT DISASSEMBLE" written on them. Why? I don't know? Probably because they want you to buy a whole new set of cups for 30 quid or so instead of a couple of the standard bearings they hide for a fiver or so (try your local bearing supplier or eBay)?

If you want to ignore Shimano's instructions? Here's how. This is done on an XT setup but others are similar. Obviously I doubt any warranty would be honoured if you do this? You proceed at your own risk!

 

You'll need two 6805 bearings (dimensions 25x37x7mm) - the more sealed and the better quality - the better.

tools needed

  • 5mm allen key
  • Hollowtech II Install Spanner & Tool
  • Small flat screwdriver
  • Hammer
  • Punch or suitable drift
  • Headset press (or threaded bar and suitable washers/spacers)
  • Supports (couple of short lengths of 3x2 wood are fine) for holding the cups while knocking bearings out
  • Teflon grease
  • Copper grease
  • Rags
  • (rubber mallet)
  • (Stanley knife)
1. Remove the plastic cap from the non-drive side end of the axle with the install tool. Undo the two 5mm clamp bolts. Remove the non-drive side crank.

2. Remove the drive sidecrank by pulling it out. A tap on the other end of the axle with a rubber mallet may be required?

3. Remove the bottom bracket cups using the Hollowtech II Install Spanner. Note: the non-drive side has a standard thread. The drive side has a left handed thread. The cups usually have markings on them to help with this! Remember what spacers you have on which side.

4. Prise the plastic covers off the cups. Be careful! There is a rubber seal underneath which you don't want to damage!

 

5. Prise the seals off the bearings. Be careful not to damage or bend them.

 

6. Support the cups and knock out the bearings from the back. Work your way gradually around the bearing slowly until it pops out. This stage will take a bit of proper hammer usage!

Give the cups a good clean.

Give the thread in the frame a good clean.

 

7. Refit the cups to the frame. Don't forget the plastic central sleeve inbetween them and the spacers. Use copper grease on the threads. Remember which way each tightens from step 3?

 

8. Make sure the bearings are well packed with grease. I usually prise the seals off with the tip of a stanley knife then pack them with good quality Teflon grease.

9. Smear a coating of grease inside the cups where the new bearings will sit.

10. One at a time - press the new bearings into the cups. I use a headset press and one of the old bearings (see picture) to do this but you could easily and cheaply make your own press with some threaded bar etc from a DIY store.

11. Smear the bearing tops with grease and then re-insert the rubber seals and the plastic covers.

12. Push the drive side crank back through (don't forget to put the chain round it!). Grease the splines and then attach the non-drive side crank. Insert the plastic cap and tighten it up using the install tool. Nip up the two allen bolts (not too tight) alternating between the two.

Comments   

0 #11 CJ 2014-01-31 03:36
PS. THIS IS NOT A SIMPLE BEARING SWAP.

You actually need a 25 x 37 x 6 bearing - still called a 6805 N

The cover in STEP 4 has a shoulder that is 1mm. If you use a 25 x 37 x 7 the cover will not full seat all the way down :(
+1 #10 CJ 2014-01-30 02:35
Do you remove one of the new 6805 seals and reuse the seal from STEP 5?

I am asking because the seal seems to have a very specific raised center section.

I have fully sealed 6805 stainless bearings I am going to install. Can I leave them sealed and re-use the covers from STEP 4. If so would your recommend putting grease on the outside of the bearing seal between the bearing the the cover from STEP 4?
0 #9 Administrator 2013-10-21 15:10
The spacer I was referring to is the plastic cover being removed in step 4 above. This actually presses inside the bearing making it fit the crank axle.


Sorry for any confusion in terminology.
0 #8 STEVEN MC DIARMID 2013-10-18 19:18
when you say spacer do you mean the long plastic tube inside the bb ? is the spacer in any of the pics above?
0 #7 Administrator 2013-10-02 07:26
Quoting stengis40:
I just tried this refurb without success as these 6805 bearings have a 25mm centre and the hollowtech crank shaft is 24mm, the extra 1mm causes a bad wobble on crank. I held my old bearings against the new ones and the difference is clear , I then looked up the make of the old ones and they have a 24mm centre that fits perfectly on shaft with no play,not sure why these 6805 bearings are suitable? am I doing something wrong? the ones that worked for me were made by enduro and size is 24x37x7 , hope this helps anyone and any feedback would be good,cheers

Did you have the plastic spacer in? The crank shaft does not sit directly on the bearing in a standard set up. However you can get bearings that remove the need for the spacer. If these have previously been fitted to you BB it would explain the difference?
0 #6 STEVEN MC DIARMID 2013-10-01 20:09
I just tried this refurb without success as these 6805 bearings have a 25mm centre and the hollowtech crank shaft is 24mm, the extra 1mm causes a bad wobble on crank. I held my old bearings against the new ones and the difference is clear , I then looked up the make of the old ones and they have a 24mm centre that fits perfectly on shaft with no play,not sure why these 6805 bearings are suitable? am I doing something wrong? the ones that worked for me were made by enduro and size is 24x37x7 , hope this helps anyone and any feedback would be good,cheers
-1 #5 Owen 2013-07-19 16:36
Thanks for the article.

I just tried this with a RaceFace X-Type bottom bracket. Sadly, the RaceFace BB has a smaller diameter hole at the back of the bearings, so there is no way to access the inner race of the bearings from the rear of the cup with a punch or drift. I can think of no reason why it's designed like that, other than to prevent the removal and replacement of the bearings and to deliberately render the whole thing useless once the original bearings are worn and to force you to buy a complete new bottom bracket.

I elected to buy a Shimano XT bottom bracket instead and looking at the cups, I can see the inner edge of the bearings from the back and should be able to replace them as per your instructions when the time comes. :-)
0 #4 Stewart 2011-03-04 14:06
Nice Article, I was struggling at stage 6 tapping the old bearings out. I then used the bottom bracket spanner to hold the cup, held the spanner in place under foot and then tapped the bearings out quite easily .

Seen the bearings on ebay for a couple of pounds each so aint spending
0 #3 Stuart Smith 2010-07-14 12:59
www.enduroforkseals.com/sitebuildercontent/sitebuilderfiles/hollowtech2a.pdf
0 #2 Stuart Smith 2010-07-14 12:56
I have just ordered some new bearings (not arrived yet) for my HT2 BB from EnduroForkSeals, $25 (inc. deliv):

www.enduroforkseals.com/sitebuildercontent/sitebuilderfiles/hollowtech2a.pdf

The instructions say that you no longer need the outer plastic seals, as the bearings are sized to fit direct on the crank axel.

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