mountaindave 

I recently got a 7s Shimano Tourney freewheel to update a Japanese-made Nashbar Sport EX for my wife and discovered an oddity about the freewheel - the threaded cog that locks everything together was spaced for a 6s frewheel, not a 7s. It was visibly noticeable. I couldn't get the freewheel in the frame with enough clearance for the seat stay.

Anybody else ever experience this? Why make the first position spacing so much bigger than the rest of the freewheel?

Bike tinker man

A photo & the exact Shimano part number would be helpful, I've a couple of these older ones myself & I'm trying to understand better what you are saying

ThermionicScott 

Someone else got bitten by this!

I bought one about a year ago, intending to convert my fiancee's bike to indexed shifting, but the first and second cogs were a full 1mm further apart than the rest, so it was impossible to set up. I ended up installing a spare 7-speed cassette wheel and life was good. I guess the QC on those freewheels isn't the best, or maybe it was just a bad batch where the wrong cogs were used.

ThermionicScott 

It's an MF-TZ21 freewheel, 14-28. Here's a picture, although it's hard to capture a 1mm difference with an iPhone:

dddd

The shifter's throw to the smallest cog position is actually much larger than the other cog's spacings, so it looks like the freewheels are being made such as to possibly take advantage of the added cable travel for a more-robust shifting to and from the smallest cog.
Note that most 7s hubs, including Shimano 7s freehubs leave at least 6mm of clearance between the face of the small cog and the toothed locknut surface, so likely that plenty of clearance is expected to be there.
On this same topic, note that this extra 2mm of clearance allows Shimano 7s freehubs (and many other 7s hubs) to be re-assembled with 2mm less spacing on both ends of the axle, making a 122mm over-locknut width with no re-dishing and no shortage of dropout clearance in most instances. So 7s on a 120mm or 121mm vintage frame is really no problem at all if the dropout is free of protruding hanger bolt/nut hardware or axle stop hardware.

Another weirdness I've come across a few times has to do with 5s freewheels, I've come across two different popular brands where the spacing is quite a bit wider than standard 5s.

The spacing was wide enough to cause severe "skating" when used with 8s chain, so these are apparently intended for use on the cheapest bikes where 7.9mm-wide chain is still in use. I suspect that again, more-robust shifting is sought, to make up for poor cabling, and possibly with a revised indexed thumb shifter of the plastic variety.

ThermionicScott 

^^ Intriguing hypothesis, but I couldn't get that freewheel to index properly, no matter what I tried -- I could get the largest 5 or 6 to work, or the smallest two or three, but never all 7. This was with brand-new Shimano 7-speed shifters, Shimano RD, new cable/housing. My vote is still that some doofus accidentally mixed some 14T cogs from the 6-speed hopper into the 7-speed FW bin.

My 6-speed MF-TZ20 from about the same timeframe has fairly even spacing from top to bottom, and now that I compare the two, the 14T cogs look identical. Hmm...

mountaindave 

Thanks for the photo, TS, that's exactly it and I can clearly see the spacing difference.

Your argument makes sense, dddd, but unfortunately does nothing to help an indexed C&V 7s. Fortunately for me the only question was one of fit, not of indexing. The bike has a pre-SIS 600 drivetrain.

My solution was to set my calipers to 5mm spacing and spend 10 minutes on the disc grinder. Presto! Proper spacing.

dddd

That's really fortunate that your freewheel has a threaded small cog!

For years, Shimano's HG freewheels used a proprietary lockring that was a royal pain to remove and to re-install to a reasonable level of tightness.

So I'm guessing that if your hub and frame gave sufficient clearance, that your shifter would in fact index this thing properly, given that the last shift throws enough cable to let the derailer come into hard contact with the hi-limit screw even with somewhat friction-plagued cabling.

And what exact shifter and derailer are you dealing with on the Nashbar Special? An original 7s freewheel installation should have left considerable room to spare for a freewheel perhaps 1mm wider than expected! Any other changes? Original wheels/hubs?

As I mentioned, there appear to be some new 5s index-spacing freewheel standards out there, but this would be the first I've seen in a 7s version.

mountaindave 

My wife's bike was formerly a 6s friction setup. It's still friction, but now 7s. I have yet to see if I need to redish the wheel - I'm hoping this is enough to prevent that.

I went through this ordeal with an '85 Specialized Allez last summer, but I used a new Suntour freewheel. It had no such spacing issues, but was larger overall than the 6s FW it replaced and the wheel needed spacers moved around and thus a redishing. I was hoping that a Shimano FW would be thinner.

dddd

Suntour 7s freewheels are narrower between the largest and smallest cogs than are Shimano 7s freewheels, but only slightly, and both brands position the largest cog in about the same position off of the seating surface at the base of the hub's threads.

Bike tinker man

Very interesting reading & situation.

I've three of these freewheels two are fitted, & one is new, I've now checked the two on the bikes & their spacing is the same between 1st & 2nd cog, but the bike which is stripped down, the freewheel is badly worn so I've purchased a replacement, & both these (old & new) there is a difference in the spacing as mentioned between 1 & 2 cogs both being Shimano ? The two fitted are both index operated, this rebuild is friction.

mobilemail

I just paired a Sunrace 7speed freewheel with 600 shifters with no issues. It appears the surname quality may be better than the old days.

mountaindave 

As the cycling world seems to have given up on low-normal derailleurs, this will work for the average derailleur. But if an unsuspecting Joe happens to have a low-normal derailleur, this won't work. Highly unlikely as I believe most low-normals came out after the introduction of 8 speed and they were not put on department store junk with 7 speed equipment. I have one on a 9s "comfort bike" with a mega-range cassette and I simply love it. Makes the shifters really easy to use - large button of the click-shifter equals larger gear for both front and rear. Can't dump three gears at a time, but with the spring pulling the derailleur down, it's still just as easy to shift down.

But I digress...

dddd

Speaking of low-normal derailers, these will work very poorly with Shimano's asymmetric-spaced SIS-7 freewheels or cassettes, since the SIS-7 shifter's own cable-travel asymmetry is effected at the wrong end of the cog stack when the low-normal derailer moves backwards in response to cable movements!

Little known fact is that Shimano's SIS-7 spacing has from the beginning used 3.1mm spacers for all but the 2-3position (that's between the 2nd and 3rd-smallest cogs). The 2-3 position spacer is fully 3.3mm, intended as an aid to shifting as the cable feeds nearly all the way out and when spring tension is thus at a minimum.

As for the last 2 cogs (smallest, 1-2 position), the spacer here is "normal" 3.1mm, but the cable throw from the SIS-7 shifter is much greater, more like 3.5mm, so only the hi-limit screw can set the indexing over the smallest cog.
All of this is to preserve the indexing accuracy as the derailer spring's tension falls off toward the small end of the cog stack.

I note that all other SIS cog sets from Shimano use symmetric spacing, including 5, 6, 8, 9, 10 and 11-speed freewheels/cassettes.

Here then is a main reason why SIS-7 shifting tends to be so robust in terms of being relatively insensitive to old, neglected cabling, and why low-normal derailers don't work right with SIS-7 drivetrains.
One can, however, position the black 2-3 spacer at the other end, in the 5-6 position! This will restore proper indexing on cassettes (only) where the cog spacers are all of the same diameter (thus does't work on freewheels).
Noting again that "2-3" refers here to the 2nd and 3rd-smallest cogs, and that "5-6" refers to the 5th and 6th smallest cogs (per old-time freewheel-building convention!).

mountaindave 

With the cheap-o FW we described, the spacer is built into the smallest cog, so you're stuck with that spacing... unless you treat it to an evening with a sand paper disc in the bench grinder...

dddd

I was only referring to the 2-3 position spacer needing to switched for use with a low-normal derailer, since you mentioned low-normal.

But like I said, it doesn't easily apply to freewheels, only to cassettes, since the spacers are different diameters at opposite ends of a freewheel.

Darth Lefty 

I'm going to spend this post to add the word SHIMERGO to this thread because it has interesting relevant information.