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PostPosted: Thu Jul 03, 2014 6:30 am 
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I have an Outland mtb frame built used in 2005 with subject cranks from 2004 or 2005. I decided to clean it up real good after 9 years. Removing the cranks was pretty straightforward, but leaves me a bit perplexed. #1 - that end cap thingie on the left side, requiring a special tool (Park BBT-10 for example) - what the heck does that do, anyway? It's like a glorified dust cap that requires a special tool to remove. I used a screwdriver and a hammer to bang it around a couple strokes to loosen it, then undid the rest of the way with my fingers. #2 - after crank removal, I popped out the black plastic "dustcaps" with a pocket knife, removed the thin inner washers, cleaned everything up, added some grease, etc. I noticed that these black caps cover the bearings completely on the inside of the BB.

So, I guess my questions are...

1) The BB sealed bearings are behind the black plastic "dustcap" on both sides, then the crank slides through it and mates with the opposite side. Does this plastic thing then rotate along with the sealed bearings? If not, is the axle just rotating on this plastic sleeve on both ends? Yes, I'm a dolt, but for the life of me I couldn't figure out what good the bearings do when they're completely covered by the black plastic thing.

2) What useful purpose does the screw-in cap on the left crank arm serve? The allen bolts seem to bind the left and right arms together, and of course there's the little pre-load schmee-load washer on the inside of the left arm, but I can't fathom why I needed to (supposedly) get a special tool just to basically hand-torque this cap before tightening the allen bolts.

OK, I'm an old school cones and races guy, so have some sympathy.


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Posted: Thu Jul 03, 2014 6:30 am 


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PostPosted: Thu Jul 03, 2014 6:49 am 
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The special cap is there to sell special tools. If you were to buy a specific high quality set of tools for every bb 'standard' on the market, you would be out thousands of dollars...


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PostPosted: Thu Jul 03, 2014 6:55 am 
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The plasic cap sets the bearing preload. It doesn't need a lot of torque, which is why the Shimano tool is just a small serrated plastic wheel with an interface to the cap. I usually use a small coin if I have to adjust the preload out on the trail.

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PostPosted: Thu Jul 03, 2014 5:56 pm 
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Thanks, yes, I understand the whole "special tool" profit center. This one could just be a flat screwdriver interface or an allen key, and @Marin that's a great tip to just use a coin out on the trail.

I still don't comprehend how the axle spins on the BB bearings. I guess the black plastic bearing cap has to spin with the bearings, but just seems like a lot of extra friction in the design.


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PostPosted: Fri Jul 04, 2014 1:15 pm 
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Location: Midlands, United Kingdom
The preload cap goes nowhere near the bearings...

The axle that goes across is in a tightish fit to the two inner bearing races, the inner faces of the cranks are tightened to the outer faces of the inner races, it works the same as pretty much any other BB, it's just the bearings are further apart.

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PostPosted: Fri Jul 04, 2014 6:14 pm 
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Don't want to dwell on it, guess I'll look at it again next time. Neither the spindle nor the crank arms directly contact the bearings - contact is via the black plastic bearing cap. This cap is a pretty tight fit into the BB cup and it just seemed like the cap edge has to rub against the BB cup when the crank spins. Perhaps I'm not explaining it very well. I'm used to the Campy UT design on my road bike, where it's clear that the cranks are spinning directly on the BB bearings without any cap/seal in between.

Bottom line though is it's back together nice and clean, and spins fine.


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PostPosted: Tue Jul 08, 2014 7:58 pm 
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Location: North Augusta, SC
You must not ride the bike much if you're still using the same BB after 9 years! I only get about 2yrs on mine, I do ride a lot of creek crossings though.

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Posted: Tue Jul 08, 2014 7:58 pm 


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PostPosted: Tue Jul 08, 2014 10:13 pm 
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Very dry here, it's been through a lot of mud but never submerged the BB. Rode it quite a bit prior to 4 years ago but I flipped back to mostly road riding since then. BB still seemed to be in good shape but the old Outland rear suspension has developed too much side to side play in the bushing under the BB. That's actually why I pulled the cranks, so I could better diagnose the suspension issue, but I'll save that topic for another thread... I'd have to take most of the rear end apart to service that one bushing... has been a fun bike to ride though. The original virtual pivot point design.


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