Ofmega spindle replacement
 

This Ofmega spindle has seen better days and is pitted on the bearing surfaces. Since Ofmega spindles are not exactly common items I'm looking for a substitute. This is where it gets a little confusing. According to the Sheldon Brown Bottom Bracket Size Database (https://www.sheldonbrown.com/bbsize.html#ofmega), Ofmega uses a unique size and nothing else works:

Ofmega (Avocet)
Ofmega cranks, including those branded "Avocet" use a non-standard spindle, thinner than either J.I.S. or ISO spindles. As far as I know, nothing else works.

But according to my admittedly rather crude measurements, it has the same taper size as a late model Campagnolo spindle I have laying around which would make it ISO I believe. I'll make some better measurements when I get home tonight but I'm wondering if this might be a Campy clone. That would certainly make it easier to find a replacement. Does anyone have any experience with this?

https://cimg2.ibsrv.net/gimg/bikefor...70a3b5153a.jpg

-----

The ring to indicate the drive side is a feature have not before seen.

Perhaps to assist a team mechanic working under lantern light following a day's stage... :D

You do not mention the model of your set. If OFMEGA brand, be it Forgiato, Competizione or Mistral? The Competizione model spindles I recall have a bit nicer finish so I was wondering if it might be a Forgiato set; a model have not had occasion to work with.

​​​​​​​-----

...there were a couple of generations of Ofmega cranks and spindles. The later ones used a size and taper that was more or less standard.

The earlier, smaller ones are quite unmistakable, and if yours fits on a spindle with similar measurements to a standard Campy, you should be OK with just about anything as long as you allow for the differences in how a JIS spindle will affect your crank position and chainline/Q factor.

Thanks 3alarmer, I suspected something like that with this one. I don't know exactly when this crankset was made or even remember how I got it but with my crude measurements and just test fitting the parts together with a Campagnolo crankset it seems to be the same as Campagnolo. I should be able to pick up a Campy spindle pretty easily. Might even have one in the parts box somewhere but I'll have to look.

I'm not at all sure as I don't even remember how I came by this crankset. I'll check when I get home to see if there is a name on it. Based on what I see online right now, the crank arms and spider look like Forgiato but the chain rings look a little different, more like 70s Campy Record clones.

-----

Thanks for the response.

There was an early version of the Competizione back when the OFMEGA badge first launched, ca. 1966, which may have come with a spindle resembling yours.

http://i68.tinypic.com/s2tnw8.jpg

It subsequently evolved into a "bis" version.

http://i65.tinypic.com/2ho9shh.jpg

There is an iteration of the Forgiato which fits your description. There is also the Gran Premio model which is above the Forgiato and below the Competizione, CX, Mistral; see catalogue linked to below.

http://i63.tinypic.com/29dgz95.jpg

http://i64.tinypic.com/i1xope.jpg

IIRC at least some Forgiato spindles are black oxide finish.

Found this image of a complete bottom bracket assembly with a ring/groove indicating the drive side like your example. There appear to be markings on the flat of the NDS spindle end.

http://i67.tinypic.com/n49u9e.jpg

The only online catalogue for these products I know of is here; it hails from 1983. AFAIK close of play was ~1985.

http://velo-pages.com/main.php?g2_itemId=69479

-----

-----

Thanks so much for this post. :thumb:

Had been wondering about this very matter - as to just how large was Sheldon's sample size and was there variation over time.

Much appreciated. :)

​​​​​​​-----

Mine has chain rings like the Competizione shown here but otherwise looks like the Forgiato shown below.

How long is your current spindle, and is it for an Italian or English BB? I may have an Avocet/Ofmega spare, or something that will work.

117mm with a 5mm offset on the drive side, Italian BB.

------

117 is the standard length for the Peyrard (NERVAR) Star series chainsets as doubles.

Sutherland gives values of 75.5 for centre width factor and 8.5 for axle end factor.

Unfortunately, IIRC Peyrard does as do T.A. & Stronglight and make their Italian thread cups one mm thicker than their BSC and metric cups so they do not have to offer a spindle for 70mm.

So you would need to change the whole thing.


-----

That Sugino Mighty in the parts box is sounding better and better :lol:

+1 this. You can mount an Ofmega crank on an ISO spindle, but it will sit slightly further out than would an ISO crank on that spindle. Take that into account when selecting your spindle length.

Perhaps this might help:

http://www.os2.dhs.org/~john/spindle-taper.jpg
Source: Sutherland's 4th Edition

Thanks John, this is very helpful.

-----

this would be my go to choice if i had an MW 70...


-----

From the chart with the gradient lines, it appears they are showing that the maximum difference in mounting position from the end of the spindle would be 2.5mm if going from the smallest (Ofmega) to the largest (JIS, i.e. Maxy).

But what they are trying to say at the bottom of the chart, "left" vs. "right", etc., makes no sense to me.

This is why I always keep an assortment of bb's/spindles around, even a bunch of dead ones, so that I can make relative measurements in real time with my work without interpreting anyone else's sizing opinions, and make test-fits on the fly.

To the OP, I would firstly evaluate where the existing cranks sit, if they are symmetrical about the bb at the pedals, and if the chainline is optimal for your setup. Then take it from there!
I would not hesitate to try to substiture a modern Shimano or Tange cartridge bottom bracket if the pedal symmetry and chainline are made happy.

My measurement for comparison of taper width is shown below, with the point of measurement from the spindle end being equal to the caliper jaw thickness or 1/8".
Locking the measurement and then transferring the caliper to a different spindle can tell you how much more/less that the spindle will slide into any given crank's square bore.

https://cimg1.ibsrv.net/gimg/bikefor...37b774cd17.jpg

Sorry - I don't have anything that would fit.

Ok, I made some measurements. The narrow end of the square taper is 12.41mm. The tapered portion is 16.0mm long. And the wide end of the tapered portion is 13.53mm. Based on the graphic shown below:

A) 28mm (non-drive side)
B) 57mm
C) 32mm (drive side)
D) 117mm
http://sheldonbrown.com/harris/images/spindle.jpg
The only markings are the line marking the drive side and the word "Ofmega" in the middle of the spindle.

Thanks for checking.

Another quick check of a Campagnolo spindle in the parts box makes me think it will work. It's a bit too greasy right now to get good measurements so it'll have to wait until the weekend when I can clean it and take good measurements but I'm hopeful.