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New linkages for my balfa BB7

April 4, 2010

My Balfa BB7 is the only frame I own that I haven’t built my self, I’ve owned it from new and it is one of those bikes that  is just right. I may not have taken her out for a couple of weeks but when I do she always left me with a smile on my face and the same thoughts in my head “man I love riding this bike” which is the main reason she is still in my kit. She was also known as the reliable bike, I might have a technical with any one or other of my rides but she was always ready to roll and take anything I wanted to threw at her in her stride.

So you can imagine my distress when she started making a horrible grinding noise when I was riding her home from work one night. I carry a very comprehensive repair kit with me at all times and it’s a point of pride that I am able to pretty much get anything fixed on the fly and at least get home if not fix the problem better than any shop. But this was not going to be one those nights. I pulled over and checked the rig over but could not pin point where the noise was coming from, thinking I could make it home I kept going but at 1/3 of the 12km ride home the noise was getting worse so I had to admit defeat. I had worked out where  the grinding noise was coming from. The frame uses a high carrier sprocket keeping the chain running in line with the swing arm,  the design is very efficient at killing pedal indused feedback in the suspension but the jockey wheel had shit itself. Due to the design there were very little options for a trail fix ( though I spent a good half hour trying to think of one) in the end it was a call to the girlfriend asking if she could pick me up one of only three times I have had to do so. STINK .

Well I pulled the rear end off the bike to see what had broken the unbreakable bike. I found the carrier sprocket had crapped itself in no uncertain terms, the factory system had a cool split machined alloy carrier that fits a 13 tooth rear sprocket between two alloy high flanges that are bolted together with three bolts. Looks bomb proof but the steel cog had worked loose and cut itself into the alloy flanges, latterly cutting the alloy in half. I figured this was the time to change the bearings on the main pivot as well so I took to dismantling the rear swing arm. After taking of the side plates, I found that they were ovalised on the tip, I had always thought that they were a bit light on in this area and now it became apparent where the major stress point was. Balfa has been out of business for a round 5 years now ( bought out by rocky mountain and in my eyes one of the biggest losses to the biking industry) so getting a new set of side plates was not an option not that I would have gone that way any way as if there is a problem fitting the same problem is only a bandaid solution.

So it was out with the verniers and ruler, lots of measuring and remeasuring and punching into cad and I had the template for a new side plate. The orignal plates are made of 5mm plate with counter sunk bolt holes I went for 8mm 2035 plate with out the counter sinking. First I sorted a small section of plate then with spray adhesive I applied the template to the plate. Next I rough cut the two templates out on my bandsaw, I then ran clearance holes in one plate and tapped M5 holes in the other plate and bolted them together,  fitted them on the mill and proceeded to cut out the shape, all went well and after a couple of days had every thing cut out. Cleaned up the edges and counter sunk for the fitting for the main pivot attachment dry fitted the new plates, all good. They are away getting anodised at the moment I’ll post shots when they arrive back and I get it all fitted up.

Stay upright..

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3 Comments leave one →
  1. Mike permalink
    December 15, 2010 2:44 am

    Those are beefy plates man. I know what you mean about bb7’s being almost bombproof. I love my bike almost as much as my wife.

    I’m gonna need new plates down the road. Would it expensive to have a set shipped from Australia to Canada? Or were these just a one time build for you?

    Cheers!
    Mike

    • December 15, 2010 1:57 pm

      Hey Mike
      I have had a couple of inquiries for the plates. if you wanted a set they will be $250 plus postage hit me up on my email if your keen.

      Stay upright
      Tarn..

  2. March 16, 2011 9:51 pm

    Balfa BB7s will never die, picking up one today, going to get it built ASAP.

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