francophile 

Hard to believe tolerances would make 1/32" (0.8mm) so important, but I bow to those who may've dealt with this before.

Pics of bike and problem bars below. Buying new bars are an option here but they need to look the same, have 1" clamp site and measure ~21" tip to tip (most I've found are 24")

Short story: Need clever suggestions to adapt 15/16" (23.8mm) bars into a 1" (25.4mm) stem. Gotta solve in 3-4 days either with new bars or a shim with some longevity.

Long story: A respected acquaintance approached me for advice on his wife's early late 60's / early '70s Royce Union 5-speed bike he wanted to fix up for his daughter to use at college (heirloom?). I offered to help him service the BB/headset/hubs and replace the bars which are rusted to hell. Got a smoking deal on eBay for NOS vintage English cruiser bars that are an exact match, but listed incorrectly as 1" clamp size (actually 15/16"). I was hoping to get by, but the headset clamp shows how much that ~1mm matters.

The bike has to be done by Friday and local shops are limited on any vintage parts, and the co-op doesn't have matching bars.

Advice?

Pics, because, honestly, it's a cool bike. I almost bought it for $30 a few weeks back, got to work on it either way.

thumpism 

Generic shim stock, otherwise known as Coke can. It was good enough for Greg LeMond's famous Tour TT win. You can see the red under the aero bar clamps.

francophile 

I was considering this if I couldn't find another solution, but seemed like it would take a couple rotations to get the correct thickness.

Soody

Cola can stock is good bling . Saves money on anodized bottle cage bolts. Scissors made to cut Alum or a good craft/roofing knife from an art/ hardware shop will make it easy.

Pompiere

With the color of that bike, a Dr. Pepper can might look better.

thumpism 

I was thinking Mountain Dew or Sundrop.

francophile 

I think he was talking about the bike in the top post, not the one @Soody posted (love that electric lime green!)

Thanks for all the feedbacks, folks. I really appreciate it. I'll give this a go later today. Gotta swing by a friend's LBS to pull the ancient Shimano freewheel today - requires FW20 I don't have and I can't hotpot it or repack the hubs, it's the last major task on the bike. I figured I'd see if there are any thin alloy shims that might work there or maybe a replacement bar, but I'm still coming home armed with a Dr Pepper can just in case I figure I can re-sell the vintage bar on eBay for at least 50% more than I snatched it for.

Something really weird about this bike. I tore down the BB and we found two dead bees and a huge pile of what looked like very shriveled rice in the captive bearing rings and throughout the BB cavity. Not just a couple, more like a couple hundred pieces. I figured someone dumped some rice down the seat tube to soak up moisture until I got to repacking the headset last night, and found even more in there, again, stuck in the captive bearings. On closer inspection, it may be some kind of flower seeds?

zukahn1 

A lot of better stocked shops should have some bar shims around 7/8" to "1 is pretty common but 15/16" to 1" not as easy to find. For this size you will likely need to make a shim if you no comfortable with a pop can you can buy assorted shim stock at a bigger hardware or auto parts supply store or individual pieces in some places or order it from amazon . For this you will basically need a small 6 inch piece of .003 inch stock to cut to size.

Amazon.com: Precision Brand Carbon Steel 1008 Shim Stock Assortment, Full Hard Temper, AISI 1008/AISI 1010, ASTM A109 for Chemistry, 0.001", 0.0015", 0.002", 0.003", 0.004", 0.005", 0.006", 0.007", 0.008", 0.010", 0.012",/0.015" Thick, 6" Width, 12"

Velognome 

Beer cans make the best shim stock

old's'cool

If you want to make a more professional job, well stocked hobby stores and machine shop supply stores will have exact 1/32" shim stock in brass and maybe other materials. Well stocked hardware stores will have larger sheets of 1/32" aluminum. You will be spending several dollars for either option. You could also try a metal supply shop or scrap metal dealer, and see if you can just scrounge a small scrap. I would recommend sticking with the softer materials, i.e. brass, aluminum, or copper, as carbon steel or stainless steel will not work so well on a 1/2" radius.
To shape the piece, first cut to the desired width but keep the full length (or at least 4-5", so you have a little extra to work with. Pre-calculate the required final length (pi*ID = 3.14*0.96875") and mark it on your strip. Then find something a little smaller than 15/16" to use as a mandrel, e.g. a ~3/4" dia. ratchet handle or piece of 1/2" nominal gas pipe; clamp this in a vise, and wrap the strip around one turn plus a bit. Tweak as necessary by hand or with different diameter mandrels until you have a complete loop with the diameter close to desired. Then cut the loop off just slightly shorter (~1/32") than what you marked, and you have a shim ready to use. End result will be as robust as you could wish for.
Shim stock thinner than 1/32" will obviously work also, if a little less elegantly, but in that case, shoot for something that factors close to an integer into 1/32", e.g. 1/64", 1/96", 1/128", e.g. Then you can have an integer number of wraps. I assume the math is obvious, but let me know if clarification is needed.

uncle uncle

Yes, because, by default, you must empty them first.

francophile 

@zukahn1 @old's'cool thanks for the constructive advice, we don't have a ton of easily-accessible hobby shops nearby but I have a ton of scrap metal, and in particular, some alloy crutches that I think may work perfect to cut and split for a shim. May even be thin enough for some snips to work through it.

thumpism 

I don't know. Using a crutch to repair a bicycle may bring on some undesirable cosmic realignment. Don't say we didn't warn you.

old's'cool

The crutch material will be a highly hardened grade of aluminum alloy and consequently difficult to work with; also, I'd be surprised if it's as thin as 1/32"; but, give it a shot. You could anneal it over a gentle flame; but I'm not equipped to give you specific instructions for that.

southpawboston

^^ This exactly. I used brass sheet stock from Blick Art Supply, which I'm lucky enough to work two block from. You'll need 0.8mm stock, or 0.03". In my case I needed to shim 25.4 bars to 26.0, so I went with 0.01" stock, which is approximately 0.3mm. It was very inexpensive (a few dollars) and was enough to make several very nice shims. I liked the color of the brass against the aluminum so much I decided to make the shim wider than the hbar clamp so it would show: