Shimano Bottom Brackets–Phil Wood Style
(Great for vintage Raleigh Twenties)
Since the original composition of this page, Shimano has replaced the UN72 bottom bracket with a revised (UN73) design, which (like the UN52 mentioned in this article (a.k.a. the current UN53)) does not have a removable mounting ring on the right side, but rather has the threads integrated into the shell (see pictures below). No problem! These bottom brackets can still be modified as discussed in this article per the UN52-specific information. UN72’s still turn up on ebay and in smaller shops, so I have left information on that model in situ. The only downside with the new UN73 design is that (unlike the UN72), the UN73 cannot have its cups removed and remaining cartridge unit paired with Phil Wood mounting rings threaded to “rare,” non-I.S.O. sizes (e.g. Raleigh (26 t.p.i.), Italian (wider shell, larger cup), French (both sides=right threads), or Swiss (both sides=left threads). If you have an older Raleigh with 26 t.p.i. threads, you can have a bike shop retap your bottom bracket shell to I.S.O. 24 t.p.i. and use common I.S.O. parts.
Secundum nota bene: By 19 April, 2007 Shimano discontinued the UN53 and UN73 bottom brackets and replaced them with the (according to Cambria Bikes) UN54 and UN74 models. No significant changes have been made (except some UN74’s have plastic mounting rings on the left side (The UN73’s had a metal ring). Rant alert: Given the fact that Shimano bottom brackets have stickers placed on the cartridge body post fabricatum, I can’t help but wonder whether this “new” model is the company’s attempt to recategorize current in-house inventory for tax purposes. Moreover, It is not going unnoticed that Shimano’s use of plastic parts has been moving up their heirarchy. Today’s UN74, with its integrated shell threading, plastic cup (and even hollow spindle) is the same bottom bracket as the UN52 units of years past (which was inferior to the UN72)–and some UN52’s had a metal left mounting cup! (conclude rant).
Traditional cup-and-cone bottom brackets are great (though, as of 2007, increasingly scarce), but equally great, more durable and maintenance free are Shimano (or Sugino, Nashbar, FSA, etc.) cartridge bottom brackets. With the Shimano unit, all you have to do is identify the proper spindle length you need, pop one in with a ratchet-wrench mounted tool, and ride worry-free for thousands of miles. No pin tools, no spanners, no lockrings, no frequent fine-tuning adjustments or tear-downs for regreasing. Even if (as some might claim, though I have never seen it) a Shimano cartridge unit blows up earlier than, say, a high-end Phil Wood “crank axle” (a.k.a. Gucci-speak for “cartridge bottom bracket,” you can buy at least four Shimano UN73’s for the price of one Phil Wood, and probably seven UN53’s (which have a solid spindle, (usually) a plastic cup on the left side, but the same bearings as a UN73) for the same price. Despite the ne plus ultra status of Phil Wood crank axles, it is unlikely that more than two Shimano bottom brackets will poop-out before one Phil Wood (By the way, John S. Allen has a Raleigh Twenty on its third Phil Wood bottom bracket, so Phil units are not completely, as the industry likes to say, “bomb proof.” It is worth noting, however, that John Allen is not your average cyclist).
But there may be times when a Phil Wood bottom bracket might seem a better fit for your application than an off-the-shelf Shimano. For instance, if you want to obtain two-sided chainline adjustment (to keep your bikes “Q” factor down by using the shortest possible bottom bracket spindle length, or to compensate for an offset chainline after you upgrade or swap out parts), you may want a Phil Wood crank axle. Or if your bike has an unusually wide bottom bracket shell (as on a vintage Raleigh Twenty, with its 76mm (vs. 68mm standard) wide bottom bracket shell), you may want a Phil Wood unit, for Phil Wood’s mounting rings do not have shoulders, and allow a custom fit unobtainable by the standard-width, single-shouldered, Shimano units.
Not so! It’s easy to replicate the features of a Phil Wood bottom bracket by grinding the shoulder off a Shimano UN52, UN53, UN72, or UN73. The UN72 (now discontinued) even has two removable mounting rings–just like a Phil Wood (the “adjustable” mounting ring has no shoulder and is unattached when you buy the unit; the fixed mounting ring (with the shoulder) may be removed by placing the bottom bracket in a pipe vice and removed with a punch) The UN52/3’s and UN73’s, by contrast, have an integrally threaded and shouldered (right) mounting side and an adjustable (left) side, and therefore only the adjustable (left) side is removable. Still, any of these models may be modified with little fuss.
But why modify a Shimano bottom bracket instead of buying a Phil Wood? Cost! Do the math. Or, if you have a wad of cash in your pocket, just buy the Phil Wood crank axle and go surf somewhere else. The math follows:
Phil Wood option:
Phil Wood “crank axle” ($109.00), Phil Wood lockrings ($35.00 for ISO British; $40.00 for Raleigh 26 t.p.i.), Two (2) Phil -specific mounting tools ($30.00 for two consumer-grade tools). Harris Cyclery carries Phil Wood (et al.) here.
UN53 ($25.00) or UN73 ($40.00), Park BBT-2 installation tool ($12.oo, or $24.00 if you want two), and, if you don’t own one, a bench grinder (circa $50.00).
$174.00 for Phil Wood unit (more for specialty mounting rings) vs. $87.00 (for Shimano UN53 + one mounting tool & grinder (or $114.00 for UN73 + two mounting tools and grinder). If you have already have a grinder, subtract $50.00 from the Shimano option’s total cost ($37.00 to $64.00 total); and if you didn’t have a grinder, you now have one for your next modification(s). Believe me, you will find uses for it.
So then, how do I do it?
Phil Wood-y Shimano Cups
You will need:
a Shimano sealed cartridge bottom bracket (UN52/3/4, UN 73/4, or UN 72 bottom bracket, or whatever the corresponding numbers for these models are today (because I will tire of updates));
one or two Shimano bottom bracket installing wrench(es) (Park BBT-2); and
a bench grinder (don’t forget safety goggles + ear protection).
Note for Raleigh Twenty owners (unless you have a UN72):
If you are modifying a Raleigh Twenty, you must have the frame’s stock 26 t.p.i. shell tapped out to a standard English 24 tpi thread at your local bike shop, or find a UN72 (and pay an additional $70.00 through the nose for Phil Wood Raleigh 26 t.p.i. mounting rings and consumer grade tools). Assuming you are tapping out to I.S.O. 24 t.p.i., be sure to drive the taps in deep enough to accomodate the Shimano mounting rings, which are wider than the stock Twenty cups.
Pre-step for UN72 only:
(Really not necessary, and now somewhat obsolete) If you are modifying a UN72, and for some reason want both cups removed and/or loosened (either to use Phil mounting rings with the Shimano cartridge, or to use a Phil cartridge with Shimano rings), clamp the cartridge unit into the pipe vice part of a bench vice and use a punch to free the fixed cup. You may need to rap on the shoulder of the mounting ring, or on the inner part of the mounting ring itself to dislodge it. Regardless, take care not to damage the threads. Once you have freed the right side mounting ring, you must reseat it on the cartridge before you can continue with the modification.
Procedure for all models:
Put on your safety glasses and hearing protection, and turn on your bench grinder. Hold each end of the bottom bracket axle with one hand (two ends, two hands, just to clarify). Carefully touch the shouldered edge of the fixed side mounting ring to the grinder wheel. The cartridge should begin to spin quickly as you hold the axle ends–too quickly to actually grind off any metal. Now, use your thumb–the thumb holding the non-shouldered end–to slow the rotation of the cartridge just enough to allow the unit to spin and to remove metal from the lip. As long as the cartridge is spinning, the lip will wear away evenly. Do not, under any circumstances, let the threads touch the grinder wheel, or you may find yourself buying a replacement bottom bracket. When the shoulder has been ground flush with the cup, voila! You have a full-featured, Gucci Shimano cartridge bottom bracket allowing adjustable chainline or installation in a Raleigh Twenty.
When you install the modified bottom bracket in the frame, screw in one cup fairly far (the left ring if you are modifying a UN52). Then slip the unit into the shell and tighten it. Back the left side mounting ring out a bit, and tighten the “fixed” (right) side until you have the desired allignment (the reason for all this back and forth is to get the bottom bracket to settle in both mounting cups before any real torque is applied. Misalignment can cross-thread the bottom bracket; and if you have a Raleigh Twenty, with an already-comprimised set of threads (retapped), you will be thoroughly bummed to have come so far only to trash your frame in the final step.
Last update: 04-07