Hello. I ride a late 80's Nishiki Prestige with a 42/52 Sugino crankset and a Sachs 7 speed freewheel (13-24). I got the bright idea to send away for a 36 tooth chainring from Nashbar so I could go up hills easier. The part is by Stronglight and fits perfectly on the crank. I thought what could be easier? However, there are two major problems. When the 36 ring is with the 19 cog in the rear, things are smooth. When I shift down to the 21, the chain starts intermittent chattering. When I engage the 24, it chatters continuously. It has something to do with the chainline and the way the chain is engaged by the teeth on the 36, but I can't figure out why. The second problem is one of chain slack when in any 36 gear higher than 19- the chain sags and slaps the chainstays. I could take out some links I suppose, but then this might mess up my 52 gear combinations? BTW, the chain is around 2 yrs old, a couple thousand miles on it. Geez, I messed this all up. Any advice appreciated.

go 42/36 scrizz the big ring. big rings are tough anyways

What kind of shifting do you have? Friction or indexed?

It does sound like a chainline issue - or a rear derailleur issue. If you didn't reverse mount the new ring, it's possible that your frame is slightly out of alignment.

As for the chain slack, you could see if you have enough in 52-21 to take out two links and see if it makes a difference. If not, you might need to find a longer cage derailleur, like the ones that are found on tourers. Many vintage derailleurs had long cage variants, and changing to one might actually solve both your problems.

Actually, I've talked myself into thinking you need the long cage derailleur.

Thanks for the advice. Putting on a 36/42 combination would only solve the chain slack problem, but not the chattering issue. BTW, a 52 ring is quite necessary, I often find myself in my 52-13 going downhill-spinning. Would not even try that with a 42 high-could not pedal fast enough.

so just coast down the hills man jeez.

16 tooth drop is too big for fronts. Get a triple "hybrid" derailleur (front) used for touring applications. The rx-100 is a good cheap choice. You should also get a long cage in the back most likely. an older xt is a good choice. Probably the chain is a clackin on the rear bridge of your front derailleur.

A 50-36 combination would provide the same 14-tooth drop as the ubiquitous 53-39 modern road setup.

i would check to see if the upper pulley is rubbing the larger cogs, which can happen if the chain is too long for the set-up, which is also the cause of your chain slap. shorten the chain using one of the methods described in other threads, then adjust the B tension screw if present and necessary.

1. Its not a freewheel problem. In super slow pedaling I can clearly see the chain engage the tooth on the 36 ring, and then chatter on each tooth as the chain seats on the ring.
2. the drivetrain operates smoothly when in 36-19 mode, even though the chain is more slack in this combination, so slackness is not the cause. And the 36 ring is not on backwards.
3. The shifting is fine between the 36 and 52- 16 tooth difference is not a problem.
4. The chain is not rubbing on the front derailleur
5. The frame is not out of alignment, everything works perfectly when the 42 is on

So I'm thinking maybe the 36 ring is cut for modern, thinner chains and what is happening is my older, thicker chain is a few thousands too large in some dimension and maybe what I should do is replace it.
Just a guess.

Aha! You didn't say the chattering was on the ring, and I think we all presumed it was happening on the freewheel cogs. You may be right about the chain. I still think a longer cage derailleur is what you need to take care of the slackness.

Too much chain could be part of the problem. See if there is more chain than needed when both the biggest ring and cog are used; otherwise, I think you'd have to get a derailleur with a longer cage to take up all of the extra chain when both the ring and cog are small; I can't see a workable setup where you have a loose chain.