58 PCD chainring anyone?

[mzjo]

I went to change the drive train on Philippa's Specialised Rockhopper at the week-end (it was all abit worn out!) Chain and cassette didn't pose too many problems (8v 13-26 road cassette like she already had, although the bike was originally 9v mtb cassette). I had already ordered the bits including Deore 9v rings for middle and bottom (top out of stock but not much wear anyway, the mechs and shifters were Deore so I assumed unwittingly that the rings were Shimano on rebadged cranks - top and middle looked to be so).

Comes the moment to change rings. Middle ring, no problems. Inside ring - "it's not the same!!!" So we measure and draw a silhouette just in case and I put the old ring back on dephased by 90° while waiting to find a new one.

The ring is 22t, 58mm PCD on a 4 arm crank (Deore is 64mm). The crank was marked on the inside ST9 XR and the ring CXC2 22. The crank arms are very flat section and cranked to the outside with the Specialised flash (now getting a bit faded). Anyone know what make/model this might be?

Googling has not revealed any four arm 58mm rings (although several 5 arm 58mm rings for the oddball mtb chainset that Shimano did and I thought was completely obsolete - I've got one!). Does this mean that this is an odd proprietary size that has disappeared in the myths of time?

All advice welcome although it would appear for now that replacing the chainset is the most likely outcome. The bike is a Rockhopper Geral which must date from the mid-90's; we got it secondhand in 2006 and Phil prefers it to anything else; it is now more or less modded to her tastes.

[LittleWheelsandBig]

https://www.sheldonbrown.com/cribsheet-bcd.html is a good place to start.

Specialized subcontract their components, so it wouldn’t be surprising if they used Sugino for that crank. Sugino made many of their cranks last century.

There are a few options if you search for custom or bespoke chainrings. It might be cheapest if you chase up a local small machinist.

[mzjo]

https://www.sheldonbrown.com/cribsheet-bcd.html is a good place to start.

Specialized subcontract their components, so it wouldn’t be surprising if they used Sugino for that crank. Sugino made many of their cranks last century.

There are a few options if you search for custom or bespoke chainrings. It might be cheapest if you chase up a local small machinist.

Thanks. Yes that does indeed identify the crank as a Sugino MX350. Still unobtainable though. I think that with suitable chainsets at under 40€ it will be cheaper to change the chainset than to get a bespoke chainring. Other options such as machining the outside of the old ring and the inside of the new one and brazing them together would be on except that the bike is 400kms to the north (yes 800kms round trip) and any repair needs to be "fit and forget" so playing around is not really an option.

I used to have an html programme for generating chainring profiles. It came off an american forum and even did oval rings although I think it only did the tooth profiles, not the mounting boltholes. The idea was that you printed out your chosen ring, stuck the drawing onto a sheet of aluminium, and filed! If I can find it I might see if the drawing is in a filetype that will adapt to a small CNC milling machine.

[LittleWheelsandBig]

https://www.youtube.com/watch?v=j-a7BtHSnDM might be useful.

https://www.cycleunderground.com.au/faq/ might be interesting. I saw some of his early chainrings and they looked good.

[mzjo]

https://www.youtube.com/watch?v=j-a7BtHSnDM might be useful.

https://www.cycleunderground.com.au/faq/ might be interesting. I saw some of his early chainrings and they looked good.

Thanks. That was really interesting, although I suspect that getting a ring done in Aus would be much too expensive (however lovely they might look). However I am sure that the Limouzilab CNC is more than capable of machining one like in the vid (although Manu might insist that I draw it with Blender, which will mean that the drawing process will take years longer than cutting one by hand!  ). 

Edit: "later that night!" found the chainring program. It does a circle of holes for the teeth that you then have to file to points. I can't see yet how to output in a CNC (or CAO) friendly format but undoubtedly that will happen. The author didn't intend saving the profiles, only printing them (soft dates from 2002!).

[Brucey]

mad thought; could you rework/repurpose a 22T freewheel sprocket, from an old freewheel?

You would be in good company here; IIRC several chainset manufacturers have done exactly this in the past.

cheers

[mzjo]

mad thought; could you rework/repurpose a 22T freewheel sprocket, from an old freewheel?

You would be in good company here; IIRC several chainset manufacturers have done exactly this in the past.

cheers

Funnily enough I have been thinking about that a bit late in the day. I must have several Maillard 22t sprockets, sacrificing one would not be a great hardship. But would the teeth profile of an IGH sprocket not be better, it's much closer to a new shimano 22t chainring? Are IGH sprockets that big made in non-dished versions?
 

[Brucey]

I have used HG-type sprockets as chainwheels on mid drives and even they worked (provided they faced the other way). Older sprockets had pretty much full tooth forms and make pretty reasonable chainrings.  However a sprocket from a freewheel would probably have to be taken from one of the middle positions; the bore of the leftmost ones is too large for a 58mm PCD I think.

An IGH sprocket might work OK too. SA sprocket HSL951 is flat 22T but appears to have holes in it already which are probably going to get in the way; the holes have fourfold symmetry but the chances of them being 58mm PCD are surely remote..?

cheers

[mzjo]

I have used HG-type sprockets as chainwheels on mid drives and even they worked (provided they faced the other way). Older sprockets had pretty much full tooth forms and make pretty reasonable chainrings.  However a sprocket from a freewheel would probably have to be taken from one of the middle positions; the bore of the leftmost ones is too large for a 58mm PCD I think.

An IGH sprocket might work OK too. SA sprocket HSL951 is flat 22T but appears to have holes in it already which are probably going to get in the way; the holes have fourfold symmetry but the chances of them being 58mm PCD are surely remote..?

cheers

I have actually done this with a Maillard copy 28t sprocket, I think for a TA cyclotourist inner position (it was a while ago!). The sprocket was complete, no slots for lightening or whatever. IIRC it worked pretty well, I only drilled three holes, not six, but its  working environment was less demanding than Philippa's Specialized. Funny how one forgets all this sort of detail after a few years!!

[Brucey]

this photo of HSL951



appears (predictably enough) to show the holes as being on a different (slightly smaller) PCD than 58mm. It may be possible to modify the sprocket and make it work for you nonetheless, but it mightn't be the easiest path to take.

cheers