Freewheel Question??
 

On a bike with friction downtube shifters, can 6 and 7 speed freewheels be used interchangeably without having to adjust the rear derailleur limit screws? Thanks.

I wouldn't think so...

The 7 was made to fit where the 6 went, but it is slightly wider. You probably will have overshift issues on the 6 if you adjust the stops to work on the 7. you may also need an additional washer to space out the axle nut on the axle, if the seventh cog hits the frame.

Thanks for the info.

Oddly enough, when I swapped my old Suntour New Winner 6spd for a new IRD 7spd, I didn't need to re-adjust anything. It worked right out of the box. I was quite surprised.

There's 6 speed and 6 speed Ultra.
2 different spacings.

I recently installed a 6 from a mid 80's Diamondback onto a 91 TREK 820 and didn't HAVE to touch anything, but it has friction shifters thay had been set "good enough".
(This bike is going to be a give away, so it's getting my worst parts).

When six-speed freewheels were introduced, some designs were one cog wider than the then-universal 5-speeds. Other designs used six cogs squished into (almost) the space of 5 thanks to thinner spacers. The wide design required more severe dishing of the rear wheel, and eventually led to the wider 126 mm over-locknut-dimension for rear hubs to ameliorate this. With 126 mm becoming universal, it was now possible to make seven-speed freewheels simply by adding outboard threads to the smallest cog of the "squished" six and screwing the seventh cog down on top of it. Voilà: seven in the space of a wide six (more or less.)

So depending on which six-speed you are comparing, the seven will, or will not, run without changing the derailleur stops. It's easy to tell which you have: just place them side-by-side on the bench and see which is taller. Sometimes you will find that a seven is just a little taller (less than a whole cog+spacer) than the six. (Just as a nine-speed Campy cassette is just enough taller than an 8 that it won't fit on an 8-speed hub even if you grind the dogs down to fit the splines.)

If your seven and six are not exact width matches you won't be able to swap them back and forth on the same wheel at will. You will have to space any given hub for one or the other (and then re-centre the rim.) But you can build one wheel with the six and one with the seven. Swapping wheels is easier than swapping freewheels. You will have to adjust the low-gear (inner) stop on the derailleur each time you change. But if you take care to set up the spacers on the two hubs so that the outer (smallest) cog is exactly the same distance inboard of the face of the drive-side lock nut on each hub, then you will not have to change the high-gear (outer) stop on the derailleur. This is the more difficult adjustment to make because it requires fiddling with both cable tension and the limit screw, so being able to leave it alone is worth the effort in careful construction.

According to my wheel-building notes, a "squished" six-speed freewheel needs to have 33 mm between the shoulder of the hub (where the freewheel will seat when screwed on) and the outer face of the locknut. A seven-speed needs 38 mm. These distances will allow the locknut to sit 3 mm proud of the outer face of the cog on both freewheels. This provides enough clearance for the chain to twist outward without scraping the chainstay when it climbs onto a larger cog. Don't make these clearances any larger because this will move the hub further to the left which makes the wheel more asymmetric and weaker than it needs to be.

To set up the spacers, strip all the parts off the axle except for the drive-side cone. If you are using a new axle, place only the one cone on it for now. Either way, make sure it is long enough!

Fill the drive-side cup with balls and grease and slide the axle into place with the cone against the balls.

Place a series of spacers onto the axle on top of the cone until it looks close, and follow with the keyed washer and locknut, tightening the locknut enough to compress the spacers together (finger-tight ought to do it for now.)

Measure the shoulder-to-locknut distance as accurately as you can.
Add or subtract spacers to lay in the desired distance.

Now, make sure that the length of axle that protrudes past the locknut is at least 2 or 3 mm, but not so long that it will protrude past the outer edge of the dropout when installed. (If it does, it will prevent the quick-release skewer from clamping the wheel.) Remember that the axle has to come out right on the non-drive side too, so think hard about what you are doing. 4 or 5 mm is nice, but not all stock axles are long enough to give you 5 mm on both ends.

At this point install the balls on the non-drive side and thread the cone onto them so that there is no chance of the axle falling out of the hub and dumping bearings on the floor during subsequent steps.

Screw your freewheel by hand onto the hub just until it seats gently onto the hub shoulder. Check the distance between the face of the cog and the face of the locknut: it wants to be 3 mm exactly if you are intending to switch wheels back and forth.

If the freewheel position checks out and the requisite 2-3 mm of axle is sticking out past the locknut, pat yourself on the back but with one hand only. (The other awaits finishing the left side of the hub.) Spin the freewheel off the hub and get back to work.

Tighten the locknut firmly against the cone through the intevening spacers to lock the dimension in place. This is much easier to do if you have an axle vise to hold the axle stationary without damaging its threads.

Place enough spacers over top of the left-side cone to build up the assembly to the correct over-locknut dimension for your frame. This is 126 mm at a minimum but there is no reason why you can't do this with a 130 mm frame.

Adjust the left cone so it runs smoothly against the balls with no play and tighten the left locknut finger tight.

If you have planned correctly, the over-locknut dimension will be correct and the protrusion of axle beyond the locknuts will be the same on both ends. If something is way off, either your axle is the wrong length or you have measured incorrectly.

Tighten the locknut as you normally do when adjusting bearing play -- just barely perceptible play so that when the quick release is tightened on the installed wheel, the play is removed and the bearings are not overloaded.

Slip the wheel (or hub if you haven't built it up yet) into the frame to make sure it is a proper fit for the frame as it actually is. The rim may not go through the brakes properly at this stage -- you're just looking for correct OLD at this point. You might have to adust the left-sided spacers by a half-mm or so to get it exactly right. But only the left, since the right determines the freewheel and chain clearance: don't touch it. Saving all the spacers from years of old hubs is a good habit....

"Re-dish" the rim over the locknuts as necessary so that the wheel runs in the centreline of the frame.

Build up the other wheel in exactly the same way using the appropriate numbers for the other freewheel.

You will enjoy no small sense of satisfaction each time you pop out one wheel and slip the other one in, with nothing to adjust except the low-gear limit screw on the rear derailleur. (Plus maybe the brake if the rims are different widths.)

That's all there is to it!

Wow, and I thought i was wordy.

Short answer, maybe.

Put it on a stand and run through the gears. I interchange wheels all the time. Sometimes I have to readjust, sometimes not.

^^^ Ah, but the short answer just reveals *whether* it will work or not. The long answer allows you to *make* it work when it doesn't, yet.

yes it is long but lots of good info and I thank you for it.

My personal experience matches the "long answer," above. Some hubs designed for standard 6-speed freewheels accommodate 7-speeds just fine, whereas others need an additional washer on the drive side of the axle. A 6-speed with a pie plate spoke protector is generally pretty close to a 7-speed without one, but even then I have sometimes needed the extra washer to keep the chain off the right dropout.