Classic & Vintage - Why doesnt my Suntour Corn Cob shift!

I'm having a problem with my Nishiki corn cob single chainring setup. The bottom bracket was changed to a cartridge unit. A Sugino crank was added. The chainline seems pretty good.

The Suntour ratchet thumb shifter seems to have enough travel for the six cogs. The freewheel looks to be in prime shape. I have been tinkering with every possible limit screw combination and have had no luck.

The cables housing have been changed and lubed. The highest gear and lowest gear seem to run okay but anything in the middle just grinds and skips away.

Is the Suntour 6 differently spaced than the 5 speed freewheels. Maybe the hanger is bent. The axle is spaced for 6 speeds but the frame is manually spread to acomodate the larger axle.

I'm getting really mad at this bike. It ought to run good.

Is it an Ultra-6 freewheel?

If it's a friction shifter, the only other thing I can think of is the chain being too wide.
Is this an OLD chain from a 5 or less speed?

I'd definitely try a new chain.

Neal

It is a new chain. I've checked for stiff links. The freewheel is a Suntour AL.

I'm having a problem with my Nishiki corn cob single chainring setup. The bottom bracket was changed to a cartridge unit. A Sugino crank was added. The chainline seems pretty good.

The Suntour ratchet thumb shifter seems to have enough travel for the six cogs. The freewheel looks to be in prime shape. I have been tinkering with every possible limit screw combination and have had no luck.

The cables housing have been changed and lubed. The highest gear and lowest gear seem to run okay but anything in the middle just grinds and skips away.

Is the Suntour 6 differently spaced than the 5 speed freewheels. Maybe the hanger is bent. The axle is spaced for 6 speeds but the frame is manually spread to acomodate the larger axle.

I'm getting really mad at this bike. It ought to run good.

The high/low limit is only for the high and low gears, which you say work fine. This is friction, correct? And you do know with friction you have to trim each gear to get the chain to ride in the proper spot, right?

The only other thing I can think of is, if you are using a wide chain on a narrow spaced 6 speed, and the chain will not drop onto the cog far enough to engage?

Any chance you still have the old chain that was mated to the freewheel? Put it back on and see how it works. If that fixed it, the middle gears of the freewheel are so worn, along with the old chain, that it won't work with a new chain. Replace the freewheel and put the new chain back on.

If you are using an old (very old) suntour rear derailleur, I have found that these have very little "over-through". Meaning I could not get a 5 speed rear mech to shift a seven speed cog, it just didn't have the reach. I switched to a shimano unit and it works fine. Suntour derailleur were just too well manufactured for their specific application. I have run into this problem on 5-6 different set ups and the suntour derailleur always needs to change!

I still like suntour, the cyclone/superbe stuff is great once you dial it in.