DKK

Following help in a previous thread, my crank was identified as a Stronglight 100, 86 BCD and I ordered a 28T ring, but it does not fit. The holes line up fine, but they are very slightly too small - I can’t get the nut/threaded insert to pass through from the back (the Allen headed bolts will go through, but that would be the wrong way around). Also, I note the ends that connect with the spider are round (they follow the outside diameter of the holes), rather than being almost square like the other two (and previous third 32T) chainring (and the spider is formed to accept the squarer end). Are there different types of Stronglight 86 BCD chain rings?

One other thing - does anyone have a link to a diagram showing how the various parts are bolted together? I want to make sure the washers go back in the right place. I am sure I took a photo with my phone when I took it apart but cannot find it :-(

oneclick 

That's why you have a drill.

rhm

Those little 86 bcd rings have become quite scarce in the last couple years! Not long ago I could always find one on eBay; now not so much. It sounds like your 28t ring was made to be the third ring of a triple, intended to be used with spacers. Is that how you're going to use it? The rounded spider arms shouldn't make any difference either way if the bolts are good and tight.

How big are the holes? Is there enough metal there to hold the bolts if you enlarge the holes? Assuming there is, then the tool you want is not a drill, but a reamer. You can get a perfectly good one at Harbor Freight for $3.29.



If you only need to remove a little material, you can make do with almost any tapered steel tool, such as a pair of scissors; twist one scissors blade in the hole, taking a thin shaving of metal off as you turn the scissors. Don't take off too much.

Washers? I don't think this assembly has any washers in it; at least, not what I'm familiar with. If you're running this as a triple, the order is: first the female part of the bolt, then the smallest chain ring, then a spacer, then the middle chain ring, then the spider, then the big chain ring, then the male bolt.

oneclick 

I suggested drill because (assuming he gets the correct size) the walls of the hole should be square to the chainring. While this is not guaranteed with a drill[1], it's guaranteed NOT with a tapered reamer. One end of the hole (or both, if you go from both sides) will be too big when the other (or middle) just fits; and considering the application and material such a mount will wear quickly.

As well, using such a reamer takes some skill. It's all to easy to make a hole that is not round at all, but a multiply-lobed hole, one lobe for each of the reamer edges, and of course, it is a lot easier to make the hole too big.

[1] Holes made by drills are not guaranteed to be any of the following:
a) round
b) straight
c) the same shape all the way through
d) the size you want them to be
e) where you want them to be

DKK

That order of components is exactly what I needed - thanks! I should have said spacers and not washers. I will be using it for the third ring on a triple.
It is supposedly a NOS Stronglight ring (the supplier has quite a few available). If there is only one type of 86 BSD ring I am a little surprised the holes are undersized and disappointed I need to modify. The holes need enlarging 2mm. As the male part of the bolt fits perfectly, could it be possible the ring is designed to fit on the outward side of the spider rather than inward (frame) side for a 3rd ring triple?

rhm

Well, sure, I cannot disagree. If OP has a drill press and a 10 mm bit, then that is the way to go. With that in mind, ideally the ring should have a 10 mm hole, enlarged to 12 mm about halfway through.

If he's working with hand tools, though, I stand by the reamer suggestion (a rat tail file is also an option, but requires a bit more skill). In practice it is pretty easy to enlarge a hole in aluminum, a little bit at a time, trying the bolt repeatedly, until the bolt will go through. it should be a tight fit.

DKK

..and looking at the ring more carefully, I am not sure it will be strong enough with 2mm removed - there is not much metal to play with - regardless of which tool I use. hmm...

rhm

Yeah, that's what I'm worried about. Could it be this ring wasn't made for a crank with an 86 mm bcd spider? it sounds like it should mount with shoulder bolts threaded into holes in the arms of a crank with a larger bcd spider. Velobase is not working.

oneclick 

He doesn't need a press, just a vice with a vertical v-goove (common). Hold the bit in the v-groove with just a mm or two of the lips showing, place the chainring hole on the point, and turn the ring, keeping it flat to the vice jaws. Once the bigger hole is started, raise the bit in the groove a mm or so and do it again; repeat as required.

And if he wants a stepped hole he need a counter-bore, not a bigger drill, that's a tricky part to find with the correct diameters. Much simpler to go with a straight hole and a longer bolt, if frame clearance will allow.

DKK

After this post I am allowed to attach photos...

DKK

This is why I am not confident the ring will maintain enough strength with 2mm enlarged holes. Agree?

rhm

@DKK, yes, I agree. That ring isn't going to work for you. Bummer.

@oneclick, I like that idea, I will try it.

DKK

Thanks. arrrgh! I guess not all Stronglight 86 BCD 28T chainrings are the same! Is this a well known fact/problem?
I will ask for photos and measurements before buying next time...

DKK

I think I may have an answer. There are Stronglight 86 BCD chainrings with smaller holes made for the 106 and 107 triple sets. I guess I bought the wrong one :-(

oneclick 

Having now seen the ring, I would not remove any metal at all. Get the right ring.

non-fixie 

No, no. You just bought yourself an excuse to get a Stronglight 106. Probably the most elegant triple crank set ever made.

Certainly the most elegant I have.

bulgie 

I have a 28t ring that will work for you (10 mm holes, 12 mm counterbore) and I'll trade if you want. I can send a pic or two if you're interested.

I can use the one with small holes for a Campy Super Record triple conversion. Is it ironic that the bolts I will use for the granny are Stronglight? made for a model called Mygal.

Mark B in Seattle

DKK

Good offer - thanks - although last night I ordered a replacement.