Facing a bottom bracket - is it necessary on a new frame?

Big Dave

I'm building up a bike using a new frame as the basis. I'm undecided as to what bottom bracket and chainset to go for but one thing I have seen mentioned in a lot of forums is the need to get the bottom bracket shell faced before fitting. Some people swear by this, others think it isn't necessary. I'll probably go for an external BB as I've fitted them before and know how to do it.

Given that the frame I'm building is new and hasn't been crashed/ trashed/ dropped etc do I really need to get my LBS to face the bottom bracket shell? Yes, it has some paint on the outside edges but if the paint buildup is likely to cause any problems could I not just remove the paint from the offending area myself and be done with it? The last bike I built had a steel eccentric bb housing so getting it faced wasn't something I even considered.

Any comments, advice, rants etc greatly appreciated.

ohlala!

I've just finished building my bike using new frame and didn't face the BB shell. It works fine for me as it's a square taper BB. External bottom brackets have to have the BB shell exactly paralel.

If I were you I would maybe try and sand down the paint using a fine sand paper like a 400 grit or so and then finish it of with a 1000 grit paper just to make it look good cosmetically. Then install the BB cups and the whole crankset assembly. If it is paralel the chain ring should have no side to side or up and down motion when you spin the cranks.

Have you googled about homemade BB facing tool? just in case.

Big Dave

Thanks for your feedback. To be honest I'm tempted to go for a square taper BB as I at least know that will work. My LBS doesn't inspire confidence when it comes to certain tasks and seeing as I don't want to have to buy a hideously expensive tool to face the BB shell the tried and tested route may be best.

I did check google for DIY facing tools but nothing came up. Perhaps somebody somewhere has tried it and the results were too disastrous to publish online...

dennisn

Seems to me that there was some discussion of this a while back. If I remember correctly
it was never really made clear whether facing did anything at all because the threads
in the shell are what hold things in place and if they are not parallel with each other and perpendicular to the frame then all the facing in the world won't help the bb go in
perpendicular to the frame as I'm guessing it should. In other words I think it's all in the threading. Key words in all this being "I think". Anyone??????

Dennis Noward

alfablue

What Dennis says makes sense, you could risk it, worst that could happen is premature wear of the BB cups - £25 to replace (Ultegra).

I got my LBS to face the shell, because I was supposed to, cost £15. The tool costs about £300 I think.

Wooliferkins

While expensive BB facing tools are not as expensive as quoted Cyclus are around £100. I am always amazed how non parallel shell faces often are.

dennisn

Wooliferkins wrote:

While expensive BB facing tools are not as expensive as quoted Cyclus are around £100. I am always amazed how non parallel shell faces often are.

I guess what I'm trying to say is that parallel faces don't mean that the bb is going to be in
right. i.e. perpendicular to the frame. It would seem to me that that is a function of the threads holding it. If they aren't right......?

Monty Dog

Modern machining lessens the need for facing in comparison to traditional small scale manufacture - many new frames come pre-faced.

GavH

I replaced my BB with a new HT2 type and didn't get the shell faced. My LBS reckoned in most cases it simply wasn't necessary. As has already been mentioned, premature wear and replacement of a BB which costs £15-25 is the worst case scenario. Sanding it won't make any difference because it needs to be uniform all the way around, hence the need for specialist tools. Moreover, all you might do is end up rubbing down to bare metal exposing it to rust.

Big Dave

Some interesting feedback guys.

Annoyingly I've just found out I need four new tyres for my car (and my boss won't accept me trying to do my job by bike) so my bottom bracket adventures will need to wait until next month.

There are some pretty good deals available on cranksets that come with external BBs so maybe I'll just risk it (funds permitting) and whack one on. If it ruins the bearings then I'll think about getting the frame faced.

geoff_ss

The shop where I bought my new frame last year checked the bottom bracket for me FOC. Apparently it was an unnecessary operation but at least I knew it was OK. I would have thought it worth doing particularly if the shop offers it as a free service.

btw the frame is a Kinesis Racelight TK08

Geoff

Mister W

I've fitted external BBs on two bikes and haven't faced the BB shells. The bearings are still running very well.

nicklouse

I did a Spesh carbon road bike about 6 months back ( alloy insert for the bb threads) it was WAY out.

I check all frames. Many new ones do not need it but some do.

if fitting a external bb to any old frame that has not had one fitted before gets done.

Dave Loasby

Is there that much flex in the cups to notice if the bb is out of square tho?
surely the cups will line up paralell with the threads regardless of the bb face?

Smokin Joe

Dave Loasby wrote:

Is there that much flex in the cups to notice if the bb is out of square tho?
surely the cups will line up paralell with the threads regardless of the bb face?

My thoughts too.

If the face is not parallel I would have thought that the cup will just butt against the proud section and leave whatever gap to the rest. Be interesting to hear if anyone who has never bothered to face the shell has had early bearing failure, I've never heard of it.

crankycrank

The ONLY time I have ever heard of a badly faced BB creating a problem was with my own cheap Bianchi steel bike from years ago. The Italian BB would constantly come loose no matter how much torque was applied to tighten it. Had it faced and the problem was solved. I've built a few more new bikes since then without facing the shell and haven't had any other problems. I believe the quality control has improved quite a bit over the years as well so it's even less of a problem now.

proto

It very much depends on the method of manufacture as to whether the BB cups needs facing or not. In the good old days of steel frames, the BB shell was usually a casting or a cheaper pressing which was faced and had the threads machined in before the frame was built. (lugless steel frames just used a threaded tube). Because of the heat applied to the components during brazing/soldering, there was a risk that the shell/tube could distort very slightly, thus making the threads not round and the ends not square/parallel. Thus the need for facing and thread chasing tools.

Aluminium frames, although not llugged, have a considerable amount of heat applied to them during manufacture (except my Vitus which is glued together!), and are even more prone to BB distortion during welding.

Carbon frames are bonded, using a metal (ti or alum) BB shell. Provided the shell is manufactured properly, and I'd be astonished if it wasn't, then the manufacturing method will have no detrimental effect on the integrity of the shell, thread or parallel/square-ness.

If the BB obviously hasn't been faced/chased by the manufacturer, my advice would be:

Steel frame: Chase threads and face BB shell

Alum frame: Chase threads and face BB shell

Carbon frame: Leave well alone. (but just clean up the end face with a smooth file to remove any resin/dings, but be gentle)

proto

crankycrank wrote:

The ONLY time I have ever heard of a badly faced BB creating a problem was with my own cheap Bianchi steel bike from years ago. The Italian BB would constantly come loose no matter how much torque was applied to tighten it. Had it faced and the problem was solved. I've built a few more new bikes since then without facing the shell and haven't had any other problems. I believe the quality control has improved quite a bit over the years as well so it's even less of a problem now.

Probably as much to do with the poorer design of Italian BB (both RH threads) as anything. But I'd have been very tempted to use Loctite Threadlock. It's a very good product, works well.

dennisn

Smokin Joe wrote:

Dave Loasby wrote:

Is there that much flex in the cups to notice if the bb is out of square tho?
surely the cups will line up paralell with the threads regardless of the bb face?

My thoughts too.

If the face is not parallel I would have thought that the cup will just butt against the proud section and leave whatever gap to the rest. Be interesting to hear if anyone who has never bothered to face the shell has had early bearing failure, I've never heard of it.

I'm with you guys. The threads are what guide the cups in. No matter what angle
the face is at. I would assume that the The Park tool(which threads in) would
make the face perpendicular to the threads, but still, in the end, the cups are guided in by the threads.

Big Dave

Just to update all you folks who took the time to respond to my initial post; I got hold of a cut price FSA crankset and bb from On One (their website is worth checking out for their FSA clearance as is the Planet X site) and the external bearings screwed in neatly first time around with no binding. A trial fit of the cranks seems to confirm that everything is running straight. I guess it is only time and the service life of the aforementioned bearings that will show if I'm lucky or foolhardy. So far so good though...

rnauth1418

BigDave

How has the external bracket worked out for you in the long term? I am in need to replace my broken internal BB. I would like to use an external Ultegra but I do not want to have to face my frame (financial concerns about the labor).

Thanks!!

cycleclinic

Facing a frame should cost about £10. It is a very quick proceedure and tools are nopt that expensive. external BB are good in the sense they are lighter but if durability is your thing then stick to square taper.

Also if you use a Token BB the plastic cups are removeable and the bearing used is a standard 6805 meaning that you can replace the bearings when they have worn out which is cheaper unless you go for the more expensive and more durable SKF bearings or similar.

hugenostrils

I wouldn't claim to be an expert on bikes and do not know what tolerances apply to bottom brackets.
However, the threads will hold the 2 halves approximately parallel but there is always a certain amount of play ( if there was no clearance it would be difficult to screw in). If the faces are not parallel the final tightening will put the 2 halves out of line. Whether this is significant is another matter and how far out of alignment depends on how far from parallel the faces are and the clearance in the threads.

k-dog

Holy gravedig but I agree - I wasn't getting great life out of BBs so I had my frame faced (£15) and they're lasting much better now.

ugo.santalucia

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19771120#p19771120]hugenostrils[/url] wrote:

I wouldn't claim to be an expert on bikes and do not know what tolerances apply to bottom brackets.
However, the threads will hold the 2 halves approximately parallel but there is always a certain amount of play ( if there was no clearance it would be difficult to screw in). If the faces are not parallel the final tightening will put the 2 halves out of line. Whether this is significant is another matter and how far out of alignment depends on how far from parallel the faces are and the clearance in the threads.

Finally someone talking sense... !