sokito

Hi,
my gran sport (alloy) 3 bolt chainrings are worn out.
I acquired a pair of stronglight ts bis chainrings that has correct bcd.
Here is how the chainring looks:
https://www.velobase.com/ViewComponen...=115&AbsPos=27

Here is how the gran sport crank looks:
https://www.velobase.com/ViewComponen...=115&AbsPos=46

The problem is, I can install the larger chainring using the stack bolt from GS crank, but I can't attach the smaller chainring to the larger chainring.

When I look at the chainrings of Stronglight TS, the larger chainring has holes that has same diameter as that of GS chainring, but the smaller chainring has much smaller holes (about 7mm) so that only the threaded part of bolt can fit in and therefore I can't use the hardware from GS cranks to install the stronglight chainring.

Is there any way I can get correct stack bolts? should I just drill the holes?

sokito

I looked at another photo of TS crank.. https://www.flickr.com/photos/randomm/2865007410/
and it looks like the nuts are placed outside and the bolts goes inside, which makes me wonder if they used some sort of shoulder bolt so that the shoulder can resist bearing from smaller ring...

Grand Bois

I have drilled out chainring bolt holes with great success, but I have a drill press. The back ring on this 93 is for another crank. I't's identical to a 93 ring except that it uses smaller diameter bolts. I drilled out the holes and now I have a 48X40 that works well for me. I used a 1/2" bit to countersink the nuts. You pretty much have to have a drill press with a depth stop to do accurate countersinking.

Iowegian

The nut is outside and the bolt is inside. It uses a normal bolt with a flat hex head. The crank nut has a normal lip and hex hole. The bolt doesn't engage all the way through the nut so you can use a hex key on the nut and a hex wrench on the bolt. I'm not sure how hard it is to find these but if you have enough material to safely expand the holes and a means to do so that would be an easy fix.