Bought a frame a while ago, SH but unused by previous owner. Came with headset cups installed, and bearings in a box. Top bearing wouldn't drop in.
Looked like the cup had a flat spot, so I knocked it out and pressed another one. Bearing dropped in fine to the other one when not in the frame, but once installed was a very tight fit, needed a tap with a hammer to seat, and felt super tight once in.
My theory is that the HT is slightly undersized.
Went to a bike shop, asked if they could do head tube reaming, guy looked confused, went into the workshop, came back out and asked if I meant facing. I said no and told the whole story, and he said it's not something they do.
Does my diagnosis sound reasonable, and was the shop just a bit rubbish? Should I expect to be able to find a shop that can do it? Tools seem available but expensive.
Or should I just get some 240 grit out?
Yes, absolutely. Head tube reaming (and facing) is a standard, essential frame-prep step to ensure the bore is perfectly round, the correct diameter, and the faces are completely parallel. It’s exactly what you need if you're dealing with tight headset installation, alignment issues, or paint overspray.
How you approach it just depends entirely on the frame material:
Steel & Titanium: Prime candidates. Steel often warps slightly from welding heat or gets choked up with powder coat overspray, so a ream cleans it right up. Ti can also be reamed, though it takes a lot of cutting fluid and slow, steady pressure because the metal is so tough.
Aluminum: Can be done, but you have to be incredibly careful. Aluminum is soft, so the cutters bite fast. If you take off even a fraction too much material, you'll ruin the tight interference fit needed to keep press-fit cups from creaking or slipping.
Carbon Fiber: Do not ream. Carbon frames either use molded-in aluminum inserts or are precisely molded for integrated bearings (where they drop straight into the frame). Running a metal-cutting reamer through raw carbon will fray the fibers and ruin the structure. If there's paint or epoxy buildup in a carbon shell, clean it up gently by hand with fine-grit sandpaper instead.
A quick tip if you're doing it yourself: Reaming tools are strictly directional. Only turn the tool clockwise, both while cutting and when pulling the tool out. Turning it backward even a fraction of a turn can instantly dull or chip the cutting teeth.
- Because proper head tube facing/reaming kits (like Park Tool or Cyclus) cost a fortune and require specific pilots for EC, ZS, or IS standards, it’s usually one of those rare jobs that is well worth paying a decent local bike shop a few quid to do for you.
You can possibly get a smaller bearing; 52mm can be replaced with 51.9 and 51.8 for example
It isn't really standard prep for most shops - it should have been done at the factory, ideally on a machine that was stiffer and more accurate than hand tools.
I've only made steel frames, and the head tubes generally heat deform in two ways. The holes ovalise, and also the tube slightly bends like a banana when viewed side on.
Your tight spot is most likely to be caused by it being ovalised, probably tight front-back but ok side to side.
Is there any evidence of the ends being reamed / faced at the factory, or all covered in paint? Paint can just be carefully cleaned off with a file or abrasive paper
At a pinch you can make a workable bodge and just file the outside of the cups at the tight spot so they aren't deforming onto the bearing when pressed in. I did this with a couple of early proto home made frames in preference to making the already thin tube too thin in places by reaming what would have been required. All depends hack bike Vs something fancy.
It isn't really standard prep for most shops - it should have been done at the factory
This. What frame is having the problem?
Your average bike shop probably doesn’t have these tools or the know-how to use them judging by the few I’ve worked in (head mechanic didn’t know which way a hacksaw blade usually goes). As said,weld-pull can ovalise or bend a tube, but you’d expect this to be sorted out at the factory rather than at a bike shop. I’d be looking for a specialist frame repair or frame builder to do this.
I remember having a crank brother headset on a steel frame that was just impossibly tight , got another headset and no problem, wonder if it’s a clash of the nominals.
IIRC Crank Bros headsets cups were made of steel so didn't "give" in the same way that an aluminium one does. It was certainly possible to shatter them.
Thanks all, really useful info (and some AI nonsense I didn't bother reading)
It's a Marin Alcatraz, nothing fancy, Ali 44mm top cup. I tried another cup with the same results. I'll knock the top cup out again and put a Vernier on it later, guessing it should be around 43.8 or so?
The head tube bore should be pretty much bang on 44mm - I've just checked a new bare steel head tube that isn't in a frame (supplied read machined).
To be honest I've only got a bore reamer for 1 ⅛". I've made three frames with those 44mm tubes and got away with just facing so the ends were parallel and flat (raw bores were ok with Hope cups and the bearings still dropped in).
for sure. I had a Giant that used to eat headsets. I realised one cup was at a slight angle to the other, Ended up getting it reamed, faced and a Hope BB installed. That was years ago though, so dont recall who did it.
Note sure where you are based OP but I happened to notice that 18 Bikes have this on their website.
edit- link https://www.18bikes.co.uk/workshop-job-ream-and-face-head-tube.html
...essential frame-prep...
As With BBs, Brake mounts and seat tubes; facing and reaming used to be a thing that LBS workshops seemed to think they "had to do" rather than measuring before deciding if any material removal was required.
I remember a mate who'd had his BB shell "faced" three times to the extent that it was almost 1mm short (~67mm), Why? because the shop owned the tools for facing and he kept knackering BBs so it must require facing yet again... IIRC we persuaded him to just fit a UN52 (this is back in the days of square taper) and the plastic NDS Cup took up the generally crap fit/alignment (of the threads not the end faces) and basically solved the issue. I also remember a mate having his brake mounts (IS) faced by a shop, He'd only gone in for a bleed/fresh pads service, after which he had to run extra washers to get his rear calliper centred again.
Hence I'm always cautious when people just designate any sort of irreversible process as "Essential" without any sort of measurement/inspection/diagnostic to measure the defect they think they're fixing.
Just remember the old adage; 'Measure twice, cut once' because its much harder to put material back once you've removed it.
Ben of https://www.kinetics-online.co.uk/ faced/reamed the head tube, bottom bracket, seat tube and rear disc mount onbthe cove hummer frame that I bought from Merlin (cheap) way back in 2013.
Everything needed faced/reamed, I tried to find my thread from 2013 as it has pics of the work and amount of material removed/weight saved but stw search says “No”
I use a 43.95mm reamer for zs44/ec44.
Its normally the frame out of round or undersized, however if the headset cup is oversized I would turn it down in the lathe to get the correct interference fit if required.
