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I just purchased a new aluminum MTB frame. The headset is a standard "NECO, 142, 1-1/8” AHEAD". The BB is ... I'm not sure, but is internal and threaded.

How do I determine if I need to face or ream my new frame, before pressing in headset cups and installing the BB?

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Have you asked the manufacturer what they recommend? Threaded bottom bracket, almost certainly not, headset, quite likely not, even if they have been painted over:… (Just a comment, because that doesn't actually answer the "how can I tell" question.) – armb Sep 26 '13 at 10:02
Did your purchase the frame only, or is this an assembled bike? – DWGKNZ Sep 27 '13 at 2:19
@DWGKNZ, it is a frame only. – Vorac Sep 27 '13 at 7:37
Lol, to the close vote: how does the question that I linked to, answer the question "should I face my frame?" – Vorac Sep 27 '13 at 7:38
I read that pro team mechanics face and drill a hole at bottom bracket (to let water leak out). But they probably also keep tyre in cellars, so I'm not sure what they're doing exactly. – imel96 Oct 16 '13 at 22:28
up vote 1 down vote accepted

If your bottom bracket is a sealed cartridge unit it's less important. If you're using a bottom bracket that has loose ball bearings and a spindle it's very important. Mostly the same advice goes for headsets. All this is less important than back in the day when all BBs and headsets had exposed and floating bearings inside.

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I asked at the LBS and was answered.

The frame was apparently faced at the factory, pre-painting. There was a depression several mm long along the weld. They told me not to give it a sweat.

Short depressions are not problem, at most it could allow moisture inside. But re-facing the frame could remove too much material e.g. if the depression is a couple of mm deep, the 2mm of material have to be removed.

On the other hand, when can improper facing BE a problem is when there is an elevated section, or if half or more of the area is depressed. Then, when the cups are inserted, they will tilt, the axis will not be straight, and the bearings, axis and cranks will suffer elevated stresses.

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An elevated section is exactly the reason to have a head tube faced. Head tube reamers/facers align themselves against the inner surface of the head tube at the top and bottom of the tube. If there is an elevated or irregular section on the lip, the blades shave it off so that it is perfectly square to the steering axis (i.e. it doesn't simply smooth it out.) – WTHarper Oct 16 '13 at 13:18

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