Stronglight 49d chainring teeth
 

https://i.imgur.com/rI1J2jr.jpg

Are these toast? They look rather pointed. Considering a bike purchase but there are a couple issues.

They appear to me to be very slightly hooked, but I'd say they still have a lot of life left. Old Stronglight rings had teeth that were strongly pointed even when new.

I think, based on the ones I have, that that is the typical manufactured shape of vintage Stronglight chainring teeth. As long as they're not significantly hooked, you should be good to go.

Is there such a thing as a tooth-wear gauge,, a tool to help show the difference between new and worn teeth? Seems like there's a need for such a thing.

A tell-tale symptom of worn chainrings is that there is a rumbling sound under higher torque input after a new chain is installed.

It's the same phenom as with a worn freewheel or cassette, where the new chain engages the teeth in an advanced position allowed by the wear to the driven side of the teeth, so the rollers then come into interference contact with the less-worn top corner of the driven side of the teeth, resulting in failure to engage (roller doesn't fall between teeth but instead rides atop the teeth).

With the chainring, the process is sort of reversed however, in that it is the upper tensed run of the new chain that now is forced to engage the valleys between teeth, resulting in the rumbling sound instead of outright intermittent slippage of the chain (as on a worn cassette cog).

All of the above is yet different from the case of teeth that are literally allowing a worn chain to slip across the outer diameter of the sprocket from wear that extends to the tips of the teeth (normal sprocket wear is concentrated nearer to the base of the teeth, where force is applied, unless the chain has stretched severely).

The pictured Stronglight chainring looks quite healthy/normal to my eye, merely broken in.

how I learned to "know".
with a fresh chain on a fresh chainring installed on a bike, pull radially outward from one link pin in the middle of the chain engagement with the chainring. Note the very slight displacement.
Now with a fresh chain on your worn chainring while mounted on the bike, do the same, if the chain lifts a noticeable amount, say 2x-3x compared to the new/new test.
Time to go chainring hunting.
I have seen often where bikes lived in one chainring, either small or large. those are the bikes that need replacement of one faster.

From the Bay, a "good" crankset and a NOS chain ring. Don

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The NOS chainwheel in the above image is late production.

Narhay's c/w was cut at an earlier time when the tooth profile was different.

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^^^^
+1 this. Prior to the mid to late 70s, Stronglight chainring teeth were quite pointed.

[QUOTE=JohnDThompson;20397518]^^^^
+1 this. Prior to the mid to late 70s, Stronglight chainring teeth were quite pointed.[/QUOTE

+2.

Stronglight Chainring Teeth
 

:thumb:

In my experience, I've noticed that chainring teeth tend to wear overall. They get thinner and the tooth form gets pointy like the old style Stronglight chainrings. I've never noticed any hooking like on rear sprockets.

In June of 1975 I got two sets of Suntour Cyclone derailleurs from the first shipment to reach the US. At the same time I received a set on Weinmann Carrera brakes that had just hit the country too. Put them on a new frame I had built for me by the folks at Gus Betat in New Orleans. I installed a new Stronglight 93 crankset and forsake all my Campy gear except for hubs.

The reason why I went with Stronglight is those sharp teeth picked up the old style latterly stiff Sedis chains better than Campy chain rings. Faster more positive shifting.

I suspect that Stronglight changed to more conventional style teeth when better shifting chains came along in the late 70's.

https://cimg4.ibsrv.net/gimg/bikefor...fd9004e2b1.jpg

verktyg :50:

A couple of points here. I believe that the wider spacing between Stronglight's rings made for a more sharply-angled chain during shifts, i.e. the front derailer cage moved further than did Campag's (or anyone elses on most non-strnglight chainsets). So the greater angling of the chain may be what helped the chain to snag the teeth better.

I think that the wear pattern on front or rear sprocket teeth has to do with one's chain-replacement intervals relative to whatever chain stretch (wear) limit that the owner subscribes to. Replacing the chain at 1/2 of 1% "stretch" as is recommended today (instead of at the former 1%) does concentrate wear nearer to the base of the teeth, so gives more of a reverse-hooked shape. While this is problematic in terms of a new chain perhaps failing to engage due to contact with the hooked corners of the driven side of the teeth, the new chain also is closer in pitch to the old chain so it takes perhaps three chain lives worth of wear to have any rumbling or skipping develop, at which time the three used chains can be rotated into service all over again. But the manufacturers don't recommend extending the sprocket's service lives out that far and there are surely at least a few reasons why (including lateral flex developing and reducing shifting performance, and the liability implications of fatiguing of the parts)

I have ground off the corner at the hooks on both chainrings and cogs, thus eliminating both rumbling and skipping respectively (Illustrated below on a single tooth of a mildly-worn cassette cog).
Bevel should be tiny, less than a mm, and at a 30-40-degree angle to the driven edge of the tooth is most effective for the least amount of material removed.

https://cimg2.ibsrv.net/gimg/bikefor...3920822d09.jpg

excellent pic!