pstake 

This is regarding vintage steel bikes with double cranks. More mechanical related than C&V, which is why I'm posting here. Question regards dimensions of suntour freewheels.

I have four freewheels on different bikes. I was using an alpha (four-prong, accushift-era) six speed, which worked great. It was a 14-28. It finally started to slip a few weeks ago, on my most used cogs.

Ordered from he Bay a "barely" used two-prong six speed with a more appropriate 13-24. When it arrived, it is in great shape and spins smooth, clean cogs, etc. ... but the spacing is quite a bit greater.

I realize that there was an "Ultra" series of freewheels but I thought that those were gone by the time the accushift stuff came around. I have an early 90s 7 speed suntour freewheel that's 14-30, and it also takes up less space than the 13-24 6 speed.

It wouldn't be a problem except that the smallest cog is virtually unusable, even in the big chainring. I know that small to small is not an ideal chainline but I've always been able to use it without a problem, on the "thinner" freewheels.

I'm wondering if there is a problem with the spacing on this new 6 speed freewheel or if i should take the cogs off and put them on the alpha freewheel body.

Hopefully you've been able to follow all that! Is my problem clear? If not maybe pictures would help?

Any advice is appreciated!

Best,
Phil

HillRider

Why is the smallest cog "unusable"? Is it so close to the dropout face the chain won't clear? If that's the problem, a 1mm or 2mm spacer added inside the drive side locknut may be the cure.

pstake 

Yes, a spacer fixed that problem. It's just that the chainline to the smallest cog is too angled, even from the big chainring. I get slippage as soon as I apply torque, and the cog itself shows now wear.

pmt

This has all the spacing. https://sheldonbrown.com/cribsheet-spacing.html

pstake 

Just when I thought I'd stumped Sheldon's vast catalog of knowledge. This was helpful. It seems that the spacing is indeed my issue. Does anyone know if the spacers are built onto the cogs or if they are separate (therefore spacers can be replaced independent of the cogs.) I haven't torn it down yet as our bike co-op does not at the moment have any chain whips available and I'm too poor or stingy to buy my own yet. Sunday I plan to have access to a chain whip, and I already have a vice and an old chain to use as the second chain whip.

Gonzo Bob

All the 2-notch Suntour FWs I've had have had all but the largest two cogs threaded on with built-in spacers and they won't go onto an 4-notch splined alpha body.

You should be able to flip the cogs of the alpha (well, all except the top threaded one) to extend their life.

pstake 

Thanks, Bob. Good to know!

DannoXYZ 

Disassemble your old freewheel and use calipers to measure total thickness of cog+spacer of each gear. Then take apart your new freewheel and grind the spacers on an angle-grinder or bench-grinder so that the cog+spacer is the same as the old one.

I've done this a hundred times on various odd-ball Suntour freewheels I had laying around to make them work with Shimano indexing. Even built 7 & 8-spd Suntour freewheels that works with Shimano systems. And even made an 8-spd Shimano Dura-ace freewheel.

dddd

I might first look for another Alpha six-speed, though those are not terribly common. They turn up on a fair number of late-'80's mtb's.

I feel that a Shimano six-speed UG or HG freewheel is the way to go here. Better shifting teeth, and these have 3.6mm cog spacers with 1.9mm cogs, so identical to Suntour's 5.5mm Accu-6 spacing.

Never flip the cogs on a Suntour freewheel. The teeth are not symmetrical, and shifting will be terrible at best. I have come across this trick after a rider brought his non-shifting bike in for service. The funny thing was that the cogs didn't even have a wear problem to begin with, so at least was easy to fix, once the problem was diagnosed...

I often ride briefly cross-chained in the big-big, but wouldn't ride in the smallest sprockets crossed over.
The chain will be slapping the chainstay, removing paint, and the stresses and wear rate over the smallest sprockets will wear them out much faster as they have fewer teeth.

ThermionicScott 

The old wisdom used to be that you spaced the crankset so that it was centered with the rear cluster, but it seems like this went out the window at some point. It sounds like your crankset may be too far outboard, and that's why the angle causes the chain to contact the chainstay. If there's a lot of clearance between the inner chainring(s) and the chainstay, you might investigate using a shorter bottom bracket next time you service/replace it.

pstake 

Very helpful DDDD ... I'm running all friction on this bike, so the Shimano spacing wouldn't be a problem, regardless. But that is very good to know. Also good to know not to flip the suntour cogs. I think that running this wider 6 speed is actually not such a bad thing. It's forcing me to be more disciplined about the way I shift, and to split time between my chainrings more than I otherwise would.

Thanks a lot for the information, everyone.