jonwvara 

I've got an old Moto Super Mirage--my rainy-day bike--that I've run as a singlespeed for the past couple of years. The problem is that all my rides end with a 1 mile grind up 10% grade on dirt. Since I hate to walk with a bike, I had the singlespeed geared so that I could barely, and I mean barely, drag my butt up the hill. For me, that's a 42-20 gear, which means meant I was seriously undergeared everywhere else. I spent a lot of time coasting on gentle downhills.
So I reconfigured it this winter as a 3 speed--a 42-tooth chainring in front and a cobbled-together 14-18-28 cassette in back. The idea is basically to have a flat and downhill high gear, a rolling-terrain middle gear, and a low bailout up-the-big-hill-to-home gear.
Okay, all that's prelude and probably not of interest to anyone but me. Here's the problem: the limit screws in the short-cage Suntour Cyclone rear derailleur aren't long enough to limit the derailleur travel to just those three rear cogs (which basically straddle the middle of the cassette for a good chainline). I thought I could easily just replace the 10 mm long screws (4 mm diameter) with 15 mm screws and be good to go, but the threading is different. Standard 4 mm screws are .70 pitch, and according to the guy at the big wholesale fastener shop I talked to, the limit screws I have are .50 pitch. He said they're not manufactured, as far as he knows.
Is he full of crap? Should I be able to find a 4 mm x 15 screw with a .50 pitch out there somewhere? Without one, my options are to insert some sort of a shim--although I can't picture a good way to do that--or to run a tap through the threaded holes in the derailleur body so they'll accept .70 screws. Or I could just shift real carefully so as not to go off the cogs. (That wouldn't necessarily be so awful, because the chain would go onto a stack of spacers at either end, rather than into the spokes or the rear dropout.) I'd much rather find the right screw. I'm not fond of tapping things out unless there's no other option--it seems so crude and final.
All suggestions/solutions will be gratefully received.
Jon V

jgedwa

If you are proficient with a tap, I think that is a good and simple solution.

If you are not, it is not that hard to learn. Go slower than you think you should. Back the tap out frequently, and use some sort of oil. And do not do it in the cold (a reminder I could have used a couple of days ago when I snapped off a cold -and therefore more brittle- tap).

Tapping pressed steel is a snap. Aluminum is pie. Surely the RD body is one or the other.

let us know how this works. I think your idea to use longer limit screws to reduce the range of the RD is a clever one.

jim

jgedwa

Thought more about this.

Putting a shim on the body so that the screw makes contact earlier would also work just fine, if you could cook up a good reliable way to adhere the shim. Epoxy under a thin aluminum or brass shim? Solder steel to steel? Or aluminum to aluminum? What other options are there?

Hmmm, the more I think about this, the more I like the tapping idea.

jim

rschleicher

I've got a possibly easier idea - just not sure if it will work. If your three cogs are in the positions that are nearest to the wheel, then it is just the "low gear" limit screw that prevents derailing on the inside. This should be more or less at the normal position, if your three cogs are where the three "lowest gear" cogs would normally have been. So, your remaining problem is to keep the derrailleur from coming off on the outside, by "relaxing" too far. See if you can adjust the shifter cable (i.e., remove slack from it while the derrailleur is on your high gear) such that the fully-relaxed position of the shifter cable and lever is still pulling in the rear derrailleur. In other words, you are keeping the cable tight enough to hold the high gear, with no slack.

jonwvara 

I'm beginning to suspect that retapping is the way to go. I know it's not hard--I've done it before and have the taps. I'd thought about trying to secure a shim with epoxy, but it's too sloppy a solution--not to mention unreliable. I'd thought about the idea of fine-tuning the cable tension so it reaches maximum tension with the derailleur in the proper position, doing away with the need for the limit screw, but that's sort of fussy and also unreliable--cable stretch, thermal expansion and contraction, that kind of thing. Plus the three cogs are pretty much in the middle of the cassette, so there's a lot of space in the "relaxed" position below the 14-tooth cog. There's no clean solution to that except a longer limit screw.
JV

jonwvara 

Just reread the suggestion about adusting cable tension. I'd misunderstood it at first. Yes, possibly that would work to keep it from falling of the outer cog. Again, though, that would be a pretty finick adjustment and subject to problems due to cable stretch, etc.
Where's the tap and die set?
JV

jgedwa

Has anyone else ever done the "limit screw extension" fix that the OP originally suggested? I have not heard of anyone doing this, but it makes perfect sense to me, and so I am eager to hear if it works.

Do it and let us know if it works!

poopncow

1. How old is that derailleur? Looking at this 76 cyclone, it almost look possible to have the limit screw heads on the inside of the derailleur. i.e. have the head of the screw bottom on the stops on the derailleur. This will but you the thickness of the screw head. Crazy?

2. I know for sure that you can't just run a 4mm .7 pitch tap thru the existing hole. You'll have to drill out all the existing threads first. Then you find the next size thread that uses a tap drill that is bigger than the hole you just drilled, drill it and then tap it. That is if there is still meat left on the derailleur.

3. A company called K&S makes "capillary" brass, aluminum or SS tubing. They come in very small sizes. what you can do is to get a oiece of brass tubing that just sleeves over the screw, cut off a small piece and epoxy that on as an entention. K&S brass tubing is available at good hardware stores, hobby stores (gas powered model cars and airplanes) and some craft/art supply stores (even michaels)

4. You can't solder alum

that should keep you busy for a while

cinco

I can't say that this is an issue which has come up in my wold before. I just went through my usual process of wandering around, looking at everything, and trying to get ideas and I'm stumped. My best suggestion is to put a small blob of solder on the end of the screw but you may have to break out the files and clean up the threads/blob-diameter before it'll go back in. I normally love square peg/round hole problems, but geez .

silversmith

Why not slip a couple of more cogs on?

infinityeye

I agree, thats a pretty big jump between cogs for an old cyclone to handle. What is the purpose? Just to have it this way (something I totally understand!)? It might not work so great in practice though.

jonwvara 

QUOTE 1. How old is that derailleur? Looking at this 76 cyclone, it almost look possible to have the limit screw heads on the inside of the derailleur. i.e. have the head of the screw bottom on the stops on the derailleur. This will but you the thickness of the screw head. Crazy?

No, not crazy. I'd thought of reversing the screw, and it might work. There's physically room for it, but it would be hard to get it started because there's no finger space. You could probably do it with a hemostat or something. I think the thickness of the screw head might make the screw long enough, too. It would then be difficult to adjust, though, because the screw head would be inacessible. One option would be to use a hacksaw blade or needle file to cut a slot for a small slotted screwdriver in the flat end of the screw (the part of the screw that would be facing upward once the screw was reversed, if you follow me). That would allow for adjustment. That's the best option I can think of, and the one I was planning to try if no one knew where to find longer screws. It's beginning to look like I'll be giving it a try.

Just a thought: Does anyone know if Suntour used longer 4 mm screws with the same threading on other parts? A lot of b-limit screws, etc., seem to be that same 4mm screw with the .50 threading. If they used a longer screw somewhere, maybe I could salvage one somewhere...
JV

jonwvara 

Quote
I agree, thats a pretty big jump between cogs for an old cyclone to handle. What is the purpose? Just to have it this way (something I totally understand!)? It might not work so great in practice though.

You and Silversmith are right, more cogs would be an easy fix. But yes, I just feel like running it with three speeds. It's one of those experiments in self-discipline or minimalism or some arbitrary thing like that. As far as derailleur capacity, I'm pretty sure the Cyclone will handle it okay. Since there's only a single 42 tooth chainring, the total range is only 14 teeth (14 to 28). And it ought to handle the 10-tooth jump from 18 to 28. I once used the same exact derailleur with a Shimano Megarange freewheel, and it moved the chain from the 24 tooth cog directly up to the 34 tooth cog with no problem at all.
JV

cudak888 

Have you tried checking other derailers for similar stop screws? Perhaps the long stops from the Campag NRs are of the correct diameter and pitch.

-Kurt

jonwvara 

For those who expressed interest, I think I've come up with a solution to the too-short-limit-screws problem. I looked over some tables of bolt and screw dimensions and found out that a standard #8 machine screw (non-metric) is a bit larger than a standard 4 mm screw--just about the diameter of the threads. Comparing the two screws, you can see that there really is a slight size difference. My plan is to re-tap the old holes for the #8 screws--there should be plenty of metal to do that. I may not quite get the full depth of the threads, but I don't think that will be a problem. I'm going to experiment with it for fit on an old busted Suntour vgt luxe before I try it on the Cyclone.
The only complicating factor is that #8 screws come in National Coarse threading (32 tpi) and National Fine (36 tpi). I'd prefer to use the fine thread because that would allow for finer adjustment of the limit screw, although that probably wouldn't matter much. Anyway, all three of the hardware stores I went to today had the #8 screws and even the tap, but only in coarse thread. I may just end up going with coarse, but I'm going to wait a bit and see if I find a fine-thread tap and a few screws. I'll post an update when I actually get around to retapping the holes.
Thanks to everyone for their suggestions.
JV

jonwvara 

Final resolution of the limit screw problem--after finding that #8 fine-thread machine screws are impossible to find--although they're a size that's supposed to exist--I decided against retapping altogether and just reversed the high-gear limit screw in its hole so I gain the thickness of the head. It took a little fiddling to get it to thread in--I used needle-nose pliers. After determining that I could thread it in a good part of its length and still limit travel as much as I needed to, I took the screw out again and carefully cut a slot in the blunt end. That lets me adjust the screw with a small slotted screwdriver. The slot isn't especially robust, so I squeeze the derailleur springs so the screw isn't under load when I twist it.
Only had to do that with the high-gear screw, as it turns out. The low-gear limit screw is turned almost all the way in, but is just long enough without reversing it. Everything seems okay--the derailleur easily handles the shift between the 14, 18, and 28-tooth cogs and doesn't shift off at either end. I haven't had a chance to ride it yet--it's been below zero here for several days--but I don't expect any technical issues at this point. Whether it's a pointless experiment in gearing remains to be seen.
JV

Avast

13 years later, thank you for that! I needed the metric screw size to get a longer screw, but the 'head in' trick got me there!

jonwvara 

You're welcome!

Looking back on it, that three-speed cog was kind of a crazy idea--my current solution to the big hill is a two-speed freewheel with 20-28 cogs and a 44-36 double crank. No derailler or chain tensioner needed since the 44-20 and 36-28 combinations have the same total tooth counts, though I have to stop and move the chain over by hand.

agnewton

Here, Here! Thanks Again!

This thread is full of good information. I've got a stripped hole for a Suntour Cyclone front derailleur limit screw and have been trying to answer some of the same questions. The derailleur is from '78. I've concluded that it's an M4-0.5mm pitch screw/ hole. Your BF thread has confirmed that I (and your previous LBS guy) aren't totally nuts. The threaded portion is 11.34mm and total length (with screw head) is 14.7 mm.

Did you (or anyone) ever try to re-tap with the coarser thread (M4-0.7mm)? Was the the adjustment with the coarser thread still OK (could you tell there was a difference)? One of the other historic BF threads (https://www.bikeforums.net/bicycle-m...ng-screws.html) recommended a helicoil as an option for stripped threads. I've found one that is M4, but with the coarser threading (M4-0.7mm not M4-0.5mm). I have not been able to find a helicoil with the finer threading (M4-0.5mm). Do they exist? Does anyone have a better source/ better mousetrap for this problem?

I like your current set-up and admire your previous, minimalist effort. If you want to try approach #1 again, you could try these fasteners I found in the amazon: https://www.amazon.com/0-5mm-Pitch-T.../dp/B07BFMZ8NF They seem plenty long and with the correct diameter and thread pitch.

Miele Man

Another thing that might work if you need a longer limit bolt of the same size and threading is to use a Dropout Adjusting Bolt. I discovered years ago that many of those are the same size and threading of derailleur bolts. I first discovered that when looking for a longer B-bolt.

Cheers

agnewton

Yeah. That would work.

DiegoFrogs

I was digging around on McMaster-Carr's website while reading this, and came across part number 90751A119. They make them in a few other lengths. Those are 16 mm long.

Edit: I'll bring the spares with me after I finish building the time machine...

nicam49

Did you know that these limit screws have a groove running the length of the thread which is filled with some glue-like substance, which I NOW realise is there and acts as a locking mechanism. Who knew! In the misguided process of cleaning the threads, I've gone and removed it, so now there's nothing to prevent the screws from being vibrated out. A search for replacement limit screws has brought me to this site, so..... Hello! If possible I'll post a pic of the offending article..

SJX426 

Instead of focusing on the RD, why not move the chain line further out with a longer spindle. Then adjust the cable on the RD to "bottom out" on the shifter, using the shifter stop as your limit controlling stop. Us an inline cable adjuster to dial it in.

ctmullins 

Maybe a tiny squirt of silicone?