Mechanical advice- headset bearings

I took my BMC in last week for a headset job, both lower and upper bearings needed serviced. They called me early in the week and let me know they’re having a hard time sourcing bearings, but they have some that seem to be close. I thought he explained they had a shorter stack height which I took as being thinner. Today when I picked it up I could see a gap between the bearings and top cap. The mechanic that did the job wasn’t there, but they insisted that mechanically it was fine. I attested that moisture and sweat at the very least could get in there. I was not happy. I still reluctantly paid my full service bill and took the bike. What do you guys think? Is it safe?

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Hmmm. I sent the pic to another mechanic and he wasn’t so sure?! Honestly these manufacturers design their products to be used and serviced one way. I wonder what BMC would think?

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It looks like there is one of two things that could be wrong with the bearing. The first is the bearing could just be taller than the original one. If they were able to find a bearing with the correct OD, ID and seat angle but not the same thickness it will just protrude from the frame like this. You still have the same amount of contact within the frame its just sticking out causing that gap. you are right though, water is now able to get straight into the bearing and will not only get dirty quickly but will eventually cause it to fail sooner just from contaminants getting. So in my opinion safe but ugly and bad for bearing life

The other possibility is they the bearing has the right thickness but the wrong seat angle causing it to not fully sit in its proper place. This could cause damage because instead of the bearing sitting flat, a corner of it would be pressing into the frame (or headset cup) and could cause damage from riding. Unless you have the old bearing and can confirm which situation it is I’d hold off on riding. If you still have the old bearing it should say the sizes on the outer race. If that’s worn off they are easy enough to measure and order yourself.


Thanks for that Chris and Joel as well.

I believe it is the first issue Chris, as when we were having a hard time finding one he suggested one with a difference thickness, I took that as going the other way, thinner some how. That is the angle they were going with as well when I picked it up. I mean it’s fully possible it’s option two as well.

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WTF, I cant see that your old bearings were so bad that they wouldnt have been better pulling the seals repaking and reusing until they could find rhe right bearing.

Can we play the guessing game of where we shouldn’t send our bike’s.

I would check with BMC and lull the bearing to at least make sure the angles are correct.


This is what I have gathered so far. They sold me a-

|Cane Creek BAA1132 | OD: 52 x ID 40 x H: 6.5 x A:36°x45°| BAA1132
|Cane Creek BAA1131 | OD: 41.8 x ID: 30 x H: 6.5 x A:36°x45°| BAA1131

I can’t find too much information on BMC teammachine bearings, but from what I’ve gathered so far they take a-

|Headset Bearing - 1.5" | MH-P16K | OD:52 x ID:40 x H:7 x A:36°| MH-P16K
|Headset Bearing - 11/8" | MH-P03 | OD:41 x ID:30.1 x H:6.5 x A:45°| MH-P03

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That is brutal. I would absolutely talk to the owner of the shop and complain. Putting in the wrong bearing is completely unacceptable for any bike let alone a high-end one. I’ve had that happen to me twice already and I now ask a shop to record part numbers for bearings when I drop off my bike. But unless I’m in a big hurry I do it myself.

I did a quick google on BMC and it is easy to find specs for the bearings. I typically order bearings for our bikes from Aire Velo in the UK. Shipping isn’t too bad and they have ~everything. And I usually order two sets whenever putting in an order so I have a spare.


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Thanks Kevin, that is one of the bearings I just ordered from the link I put above. Thanks for another source. Good to know it looks like I found one of the right one, if we both came up with that with a quick search.

It gets even worse. I wanted to give it a short test ride around my house and the headset just keeps coming loose, tightened it up with a multi tool and five minutes later completely loose. Limped it home. The owner of the shop was there when I picked it up and said they were just trying to do the best with the parts they had, and offered little recourse. And fully charged for the bearings and instal. And I really can’t afford that not that anyone can. They did offer to instal the bearings I ordered when they arrive for no charge but I think I am still stuck paying for the ones they installed.

surprising the bike shop you went to could not have done the correct thing and search for the right bearings. Im no mechanical engineer, but there is a reason they need specific bearings, tolerances are so small it will damage your bike. The bike shop should know this and not put the wrong parts in. Would this be allowed in a car? I would have my mechanics head and the shop owners! Don’t stand for it. I hate it, but social media is powerful.

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Have an update on the bearing fiasco.

Following the trail on forums and any lead I had, I tracked down the top and bottom BMC Teammachine 2019 headset bearings. After speaking with some local mechanics (thanks Tim!) I decided to bring the bike back to the shop who installed the wrong bearings as they said they would swap out the wrong ones with the ones I ordered and would refund the cost of the incorrect ones. I was apprehensive, but this made the most financial sense.

That is when the preverbal well depended. The bearings I ordered, the ones I swore were correct were not. To be clear the bottom was correct, its quite common (1.5) 52x40x7 36x45. But the top bearing was shorter than the old bearing we pulled out (H). Scrambling, I took apart the old top bearing, lightly sanded down the cups to remove some rust, made sure all the bearings were in tact in the nylon sleeve and added new grease. This is when I finally noticed, the top bearing had a what I understood as a gap, a lip in it. I wasn’t sure if the lip was supposed to be there or if the old bearing was just damaged.

So back to the bike store, I brought the new ones I ordered, and the OEM ones I tried to restore. The bottom installed fine as expected but the top did not. I mentioned the strange ‘gap’ lip to the mechanic and he wasn’t too sure. He tried the new top bearing I ordered but it still didn’t fit. He called me up and we had two options now, we can keep looking for the correct top, or we could re-install the old one refurbished up. He realized that lip, that movement I found in the old top is supposed to be there. It’s described as a ‘campy’ bearing with lip when you find them online. It fits into the steerer and that gap compresses I suppose? It creates that perfect flat top while also providing enough compression? I am still muddy.

Super long story short, we re-installed the old ones until the correct ones can be found. I finally heard back from BMC this weekend and they confirmed the correct bearing for this frame.

TOP: MR155 Headset Bearing (from BMC)