Yes, we all know how bad helicomatic freewheels are. I know they have flat teeth and don't shift as well as curved tooth freewheels. However, is it possible to make them shift properly to all gears? Have they ever shifted properly?

I have one on a bike now and it seems to upshift fine, but as it downshifts (up to larger cogs) it is very finicky and usually wants to skip over a gear or two. Specifically, the problem gears are the one or two above the largest sprocket. I can shift past those and with much clanging and gnashing of sprocket teeth it can make it to the largest sprocket and then I can upshift back to the skipped gears (if that makes any sense at all).

The derailleur & hanger appear to be straight. The limit screws are adjusted properly. The freewheel was a little sticky but I gave it a good dosing with light oil and it spins and engages perfectly now. Is there something I'm missing or is this just a usual issue or "quirk" with these freewheels?

I ran helicomatic freewheels for years. I do not think the issue is they were bad, I think when compared to some other offerings of the time (Shimano/Suntour), they simply were not as good (they had the same teeth design as Regina's and other high dollar European freewheels, just not the pinache').

From your description of the problem, I suspect the problem may be derailleur. Which one are you using and what sized cogs are you tring to shift into?

Suntour Cyclone MKII gt and the freewheel has 14-28 cogs. Could this be related to the b-limit screw?

you can try to scrounge up some 5 speed indexed thumb shifters and give those a shot.

you also might want to swap your chain with a larger or smaller size to see if it helps.

That derailluer should be fine. You can check the B-screw. If it were the chain, I would suspect that it would be a problem throughout, but still check it.

Tell me about the cables. Are the old/rusty? Is the housing floppy? It sounds as if you are getting to a tension limit as you go up the cluster, and you are loosing cable pull through housing flex. When you jam it into the top get, it gives. Kinda hard to diagnose from here.

Probably should've mentioned that I'm using downtube friction shifters. Recently replaced the shifting cables but it hasn't had an effect.

I'm still using the older (original?) housing at the back but I greased the cable when I replaced it and the length seems alright. Makes sense that that would be a problem area and I have plenty of extra housing, so I'll try replacing that to see if it helps.

I ran a Helicomatic for a while and it shifted perfectly.

The only thing I was worried about was if it would seize up from not being maintained to it's standards.

I'd think it was something else in the drivetrain other than the Heliomatic....

The Cyclone really doesn't like a 28t big cog. It'll get5 there, but it's happier with a 26. Try and find a longer hanger, screw the B-limit in all the way, and see if that helps.

coincidentally, i got my trek 520 ready for sale today, and the helicomatic actually shifts perfectly without any re-trimming. i am using an old XT RD on it though.