I posted this on the bicycle mechanics forum. I thought I'd also post it here, looking for more feedback. What I'm looking for is how to do this properly.



I changed the chain rings on my bike recently. I put a 47T inner ring on in place of the 42T that was on it. The thing is, it is very close to the chain stay (~1mm) and if the frame flexes (accelerating, cornering, etc) that ring will scrape the chain stay. Yes, the bike has a very tight rear triangle.

Is tried shimming but found it VERY difficult to do well. Is shimming is a bad idea? Here is a flat-pattern sketch of the shim I made and installed. The central cruciform structure holds the four leaves together and prevents friction form skewing the leaves during installation.

To use it, you place it on the end of the spindle and temporarily hold it in place with a crank bolt through the central hole while you "fold on the dotted lines". Each of the four arms folds down along the square, tapered bottom bracket spindle. You remove the bolt and install the crank over the newly formed shim. As you install and tighten the crank bolt, the four arms of the shim cinch down against the spindle.



I made one from 0.009" thick aluminum. The five holes were punched not drilled. The central hole was opened up with a conical Dremel grinder bit. It was not drilled because the foil is too thin. I installed it and it worked beautifully on the very first try. Remember, this is a foil, so you cut it freehand with a scissors. Total time invested in design, fabrication and installation was about 15 - 30 minutes.

.

The bottom bracket is a Phil Wood. It has already been set to the left about as far as I am comfortable doing - the left retaining ring is flush with BB shell, the right retaining ring protrudes two full turns of the threads, approx. 0.05".

The spindle is 113 mm long. The bottom bracket shell is 68 mm wide.

I am not averse to buying a new Phil BB with a longer spindle but they do cost $200. What I worry about with that option is spending the cash but not solving the problem.

If I do buy a wider spindle I might have chain line problems. I think the next step i to ensure the chain rings and freewheel are properly aligned.

Could it be a crank problem? Is the square-sided socket mis-shapen, stretched or something? It is a vintage Campagnolo NR crank but is new to me (my first use of this crank). Could it be a different taper than my spindle?

What should I do?

I went to the Phil Wood web site and read the installation instructions. It says the retaining ring design allows for protrusions of up to 5 mm (0.20")!!! Mine might be different than what he is currently selling. I bought this very soon after he first started to marketed them (~1974). When I bought it, it did not have instructions (that I recall).

I took my entire bottom bracket apart today to work on this. The Phil Wood bottom bracket has been in this bike, unattended, for more than 30 years and it is still FLAWLESS! That is called, "getting your money's worth".

To work on the chaing ring to stay spacing problem, I installed the drive side bottom bracket lock ring to it's minimum depth leaving a full 5 mm / 0.20" protrusion (allowed per instructions on Phil Wood's web site). This allows the cartridge to protrude the maximum allowable amount and maximizes the clearance between the ring and the stay. In this configuration I have 0.125" clearance which is more than enough. I am happy again.

I may or may not adjust the cartridge inboard a smidge as the large chain ring lines up with the second of the six rear cogs.

Maybe I should just call Phil Wood and get a custom spindle machined for a new BB cartridge. I could do it in titanium this time.

<several months time elapses>

Well, after several months of riding with the shimmed crank, I've given up on it. Here's my problem with it. The shim did not move uniformly during crank bolt tightening. The legs of the shim were unevenly placed inside the taper.

This means the crank was tilted relative to the axis of the bottom bracket spindle. Because of this, it behaved as if it was bent. I measured the deflection at the tip of the 49T chainring. It was 0.09" (almost 1/8"). That's a lot - too much.

The chain would rub on the front derailleur cage unless the cage was perfectly aligned. This means I was constantly fiddling with the lever to adjust the cage. What a pain! Who needs it, not me.

I am going to direct-mount the crank and go back to the 42T inner chainring so nothing rubs. I will figure out what I need and buy appropriate parts.

It is a bit of a puzzle, though. If I just move the crank outboard (reposition BB cartridge in BB shell or buy a BB with a longer spindle), it will adversely affect chainline. Perhaps I need to move both the BB spindle and the freewheel outboard. The freewheel can be moved with a spacer. The BB cartridge can be moved by moving the lock rings.

I made some additional measurements last night, too. I found the BB spindle is only 113 mm long, not the 120 mm I was expecting. The BB shell is 67 mm, not the 68 mm I expected.

If I go with a wider spindle it will certainly affect chainline. Which I will have to deal with.

I think what I'll do today is just put everything back to original equipment - 42/52 chainrings and 5 speed freewheel. I'll be sure to get the freewheel aligned with the chainrings. Once, that's done I can rethink this whole situation.

The geometry of this frame is so tight, you are limited on which chainrings you can use! I may be limited to using a 5 speed freewheel, too. Who'da thunk it?


Okay, so everything is back to original equipment now. I took it for a short little spin. It rides more solidly now. The chain doesn't rub the front derailleir cage. It shifts better, is less sensitive and shifts more easily between gears on a five speed freewheel, as opposed to a six. This is how it was made to work.

I have 42/52T chainrings and a Suntour Pro Compe freewheel back on it (14, 17, 19, 21, 24T). The gear ratios cover a wider range. The shift pattern between successive gears is decent but not great. I've put a brand new, drilled Regina Oro chain on it.

I'll keep working on it but this time, I'm going to do it right.

Cup-and-spindle BB...cup-and-spindle BB...cup-and-spindle BB

-Kurt

The real question is....why the hell would you need a 47t ring on the inside?!?!

If you really have to have the 47t inner chainring, then I would just use a longer spindle to move the cranks away from the frame. Get another 2 mm or so and that should solve most of your frame-flexing-into-the-cranks problem. You have a freewheel in the back with a rear derailleur, so moving the chainline 2 mm outboard shouldn't be a real big deal. If you're worried about it, take it out of the spacers on the drive side on the rear wheel, redish the wheel over 2 mm, and things are back to perfect.

I'm all for homemade shims on bikes, but it sounds like you're overthinking the problem. The "right way" that you're trying to do things doesn't use shims.

LOLOLOL!!!

Okay, there is an honest, legitimate answer. It is to get half-step gearing. A three tooth difference in the front makes for a sweet half-step shifting sequence. So, I had a 47/50T front ring pair.

At one time, I had a 42/45 front ring pair but it looked really strange to have such a small outer chainring.

If you want to do this right, it is actually quite tricky. The spindle I have is rather old and is only 113 mm long. 2mm more would be 115 mm which Phil Wood does not make. Then there's the issue of chain line, and the issue of a spacer moving the freewheel too close to the seat stay,...

It's reassembled the way it designed to be used - 42/52T X 14-24T with a good chain*. I think I'll ride it this way for a while.


* Did I really pay $80 for a Regina Oro chain? I must be misremembering the price.

The spacers on freewheels/clusters will fit ove the fixed cup to shim it out. Make sure you have enough space on the left side for the lock ring to fit on. Use the metal spacers rather than plastic.

What are the spacers to which you refer? There is no spacer between my freewheel and the hub. Are you referring to the spacer on the axle?

IMHO.....It appears that you are set on half-step which I really liked as a young man. If you don't need the high gears of the 52 ring I would suggest you go back to the 45/42. I don't spend near as much time looking at my bike as I do riding it......I didn't care for the looks either but it gave me the gears that I needed keep my cadence in the area I was riding at the time and I also actually had 10 gears to choose from with the 5 cog freewheel.

The big advantage to these new cassettes is you can pick the gear range that you need in the rear and it makes little difference on chain ring choice. Half-step is really an obsolete choice with modern or even semi-modern drive trains.

Not so with his sealed, big-buckaroo, Phil BB.

-Kurt

Fwiw, a longer Phil axle/BB wouldn't set you back $200 as you already have the rings. We're talking more in the range of $90:

https://www.lickbike.com/productpage....=%270155-25%27

Neal

You haven't said what manufacturer/model your crankarms are. If pre-1994 Campagnolo standard taper (Campy, of course, but also Sugino Mighty and Suntour Superbe, more or less) or a JIS-taper type, then: you could also simply buy one of the cheaper JIS-taper cartridge BBs; I like IRD ($40-55), but Shimano also makes them (more plastic than I'm comfortable with). With a JIS taper, you'd want a shorter BB than would be "double chainring spec" for a Campagnolo-standard crankset -- like 113 instead of 115; but for a true JIS-standard crank, I'd go for 116 if you have a 113 now. With a cartridge BB like this, you could shim the fixed cup. I'd recommend a steel shim for this, such as the Sturmey-Archer sprocket shim at 1.5 mm thick. As discussed above, not an option for the Phil BB, but the other cartridge units have a fixed cup with a flange.

If you have an ISO crankset (old French, maybe even new French, or post-1994 Campy), then I don't recommend the above; though others might.

This is all vintage 1975 stuff, all of it. The bottom bracket is a Phil Wood. The crank is a Campagnolo Record. The rear derailleur is a Nuovo Record. This freewheel is a Suntour Pro Compe (I also have a 14-22T Dura Ace 5 speed). The chain is a drilled Regina Oro. The frame is spaced in the rear at 120 mm.

All the original equipment gear listed installs and lines up with zero problems. It's when I try to "upgrade" to six speeds that the difficulties arise.

I understand and agree with this 100% but I'm going to leave it the way it is for a while.

I am going to research what it takes to do this right. I was thinking that one of the "right way" solutions would be to buy a triple crank which yields high top gears and a low, low bottom end. That is what prompted all this research into chainlines, etc. I'd still like to do this.

Hopefully, it does not require me to buy a "new" vintage bicycle. On second thought,...

I took the bike for a bit of a ride; I just got back. It was just about perfect exactly the way it is, the way it was meant to be.

I was thinking about this issue while riding. I feel like I am re-living the late 70-s and early 80's - trying to figure out how to get more gear ratios out of my "ten speed".

Any input on the adviseability of a triple crank would be very welcome.