jonwvara 

My PX-10 project hit a snag this afternoon when I realized that the bottom end of the down tube doesn't end flush with the inside of the bottom bracket shell, but extends about 4 mm into the shell. As a result, there's not enough clearance to insert the French threaded VO cartridge bottom bracket I bought last week.

The solution, I guess, would be to grind off the troublesome end of the tube with a dremel tool. I'd probably do that if I had a dremel tool. Instead, I guess I'll use a French threaded cup-and-cone Sugino BB that I have on hand. I'd prefer a Stronglight BB, of course, but I don't have one.

Either way, I've also got to have the BB shell chased and faced. Whatever was in there for a cup before the frame came to me didn't thread in as far as the Sugino cup I have. It runs out of useable threading a couple of turns before the rim seats against the shell. I think Onion River Sports in Montpelier has a French BB cutter. (I know that some say it's always a good idea to chase and face before building up an old frame, but I have been known to skip that step if it's not absolutely needed.)

I've never seen this protruding-tube issue before, but I'm guessing it was pretty common during the Bike Boom, when the Peugeot factory was slamming out frames like there was no tomorrow. Except that now it is tomorrow

eschlwc

another reson to prefer motobécane. B^)

3alarmer 

...
...I've been unable over the years to get French cutters for my BB threading tool with a pilot pin, which is what you really want. But you can buy just a standard industrial HS steel tap for this on Amazon for mot too much money. You only need one, and because there are already a lot of threads cut in the shell, you have reasonable chances of getting it in straight if you are careful and deliberate. I've only used mine for cleaning up threads, but it ought to cut deeper into the shell just fine if you get that tube out of your way.

The other option is to use a reamer to oversize it and thread Italian, but it's a lot more work.

thumpism 

My '78 PX10 had a similar issue except that it was the seat tube and not the down tube that intruded. At least the factory was versatile enough to produce both versions. I was installing a plastic BB sleeve that would not fit, so used a Dremel. I still have that original bottom bracket but recall mine being British thread instead of French. Ski Rack in Burlington might have the tap you need.

nashvillebill

Harbor Fright--er, Harbor Freight--has Dremel copies very cheap, they should work good enough to get you through this project and maybe a few more.

FBinNY 

I can't believe how the art of using a FILE has gone the way of Damascus steel (at least here on BF).

A half round mill bastard


will make short work of this job faster and far cheaper than using a Dremel.

If the OP can't afford a file, he can buy some medium grit sand paper and wrap it around a piece of pipe or dowel rod.

As for the threads, it may not be as bad as it seems. BBs of that era often had raised areas for the thread, and relief toward the center of the shell. Failing that it's far easier to grind off some thread from cups so they seat flush. There's still plenty left to engage the good threads. To figure out how much to remove, thread the cups in until they bottom, measure the cap, and grind 1mm more than that off the lead and you're good to go.

gugie 

+1

It's sad that you had to post a picture of one as well!

3alarmer 

nashvillebill

Well I do agree that the proper use of a file is a lost art, and a file is cheaper than a Dremel, but I dunno about faster, a Dremel with a good cutting wheel is pretty quick!

Besides, don't we all need an excuse to buy yet another power tool?

FBinNY 

This job calls for about 6 hard strokes with a file. Having done similar jobs a few times, I assure you that I could file it before you could plug in the Dremel and select and chuck the cutter.

That's not to mention the space limitations that make using a Dremel to cut the tube back to the inside wall of the shell awkward.

BTW - if you're going to use power tools, a 1-5/16" hole saw is faster. Grease the OD and use the shell to guide the cutter.

repechage

While he plugged Binford, that looks a lot like a Milwaukee Hole Hawg.

Bad Lag

A mill bastard file is unsurpassed on the end grain of wood. It will leave the end grain smooth and polished in a way that is almost impossible (or impossibly slow) with sandpaper.

Camilo

Even though I have a dremel and use it quite a bit, I would have thought "file" first just because it would look like a simple job for a round file, and it's certainly easier to be careful with a file.

I have a bunch of files, and even know a needle from a round from a three square and know what the card is for. 8-) But I was born in the early 50s and took shop class in junior high. Actually, I inherited most of them from my grandfather when I got his tools when he died. It seems I need to use my mill file every time I cut a carbon fiber steer tube just to even up my crappy cutting.

jonwvara 

I like files. I have a lot of them, and I know how to use them pretty well (although I'm not a maestro of the file like some). I'd use a file if just one corner of the tube was causing the interference. But we're talking about removing 4 mm of material across the entire end of a piece of tubing. No matter what anyone says, that's not going to happen with six hard strokes of a file. And yes, of course I could grind away at the cups rather than having the BB shell chased. But I have an aversion to unnecessarily modifying previously undamaged original parts.

My concern about attacking the protruding 4 mm of tube end with a file is that on every stroke of the file--more likely 600 of them than 6--the teeth of the file are going to come within a couple of mm of the threads on either side of the shell. I'm not sure I can do that consistently without bunging them up. Some duct tape might help, but then again it might not.

I'll likely end up taking this job to a local machine shop. Another option is to try running 1 1/4 hole saw through the opening--carefully and at low speed, again with some tape wrapped around the non-toothed body of the hole saw to protect the threading. That should give me just about the clearance I need. I'd feel better about trying that if I already had a fine-toothed hole saw, though.

EDIT: FBinNY, when I first read your post I missed your hole-saw suggestion. So we're on the same page there. I'd initially thought that a 1 5/16 would be a little big, but doing the conversion it comes out to 33.375mm. The actual opening in the shell--measuring from the tops of the threads--is 33.90 or so. That's a close fit but it likely will work. Plenty of grease on the hole-saw body should help. Goodbye to the inner ends of the rivets holding on the outside-of-the-BB serial number plate.

JohnDThompson 

Both my Viscount frames had this, except it was all four tubes (down tube, seat tube, and both chainstays) that extended into the shell. I had to file them all down before I could ream the shell to tap Italian threads.

jonwvara 

So it's not some French thing....

headset

On my PX I shortened the VO adjustable cup rather than risk damage to the bottom bracket. Not a lot of French taps around or skilled mechanics who even know what a French threaded bottom bracket is. No problems is 4 yrs of use. The bottom bracket is the disposable part, not the frame.

T-Mar

When the tubes aren't mitred, I'd rather have them protruding into the shell than not. When they are protruding into the shell, you have a stronger joint due to a higher percentage of engagement with the tube collars on the shell. This is why good frames have mitred tubes. There's 100% engagement and maximum strength, provided you get full penetration of the brazing material.

If you have problems finding someone to cut French threads another option is to have the shell reamed and threaded to Italian standard, which is far more common.

vtchuck

If Onion River isn't up to the job, I'd bet Old Spokes Home could help you out.

Lamberts & Viscounts that used the the sealed bearing BB usually had protruding tubes as well.

fietsbob

good braze bond of tube to BB shell has maximum surface .. a good thing , I suppose..


Maybe a Dremel? flex shaft die grinder¿, if using a file is not your skill set

rhm

@jonwvara, I don't think the file is as dangerous as all that, especially if you're working on a bare frame (no components attached). Get a big half round file, set the main triangle of the frame on the back porch with the BB just off the edge over the steps, sit on the main triangle to hold it steady, and file downward with pretty good force. I don't think it'll take very long.

jonwvara 

Yes, Old Spokes Home definitely has the taps. Onion River is much closer to me, but I just learned that they don't have the right taps. Or maybe they do have them, but just can't find them. I guess I'll be driving to Burlington after all.

Lascauxcaveman 

That's pretty much the exact method I imagined when the file was first suggested upthread. Since you can do one side, the flip the bike, then do the other side, you could attack it at a slight angle that would make dinging the threads less likely. It's a tight space to work in, and would require a lot of fast short strokes, but definitely doable.

I like the Dremel-style tool option better, probably just because I have one and use it on a lot of stuff. You can get a full kit with grinding stones, cutoff wheels, etc for about $30 at both HF or Costco, probably a few other places.

FBinNY 

No it's a production manufacturing thing.

The other ends of the tubes have to meet other parts, ie. head tube or frame ends, so the BB shell is where they take up errors. Given the choice to err short or long, most better builders prefer to go long rather than have a weak joint.

Back when we imported Italian frames, they used to run a specially made hole saw through the BB to clean up the tubes before tapping. On those frames, we'd see thread marks on the ends of the chainstays, proving they originally extended into the shell.

--------

Re, the hole saw. 1-5/16" hole saws are rare and may be pricey. OTOH- a 1-1/4 saw wont work without some help. If you just try to run it through the cutting forces will cam it over to the unsupported side, and you'll strike out. To make it do your job, make a pad covering the lower 1/3rd of the BB shell, to support the cutter and hold it just shy of rubbing the high side. This way it'll cut the tube more flush and not cam over.

Wilfred Laurier

My old CCM had the same problem and, while I got comfortable and settled in for hours of tedius grinding with my dremel, it wound up taking less than a minute. It had English threads, though, so I was able to have a set of taps run through to clean it up.