My prototype 1x conversion (FSA 386 pattern to 104BCD)

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  • My prototype 1x conversion (FSA 386 pattern to 104BCD)
  • ChunkyMTB

    That’s a lot of seat post!!!

    I’m a lot of guy!

    Again with my other post I found no offerings of this kind of advice whilst searching and this website pops up a lot so I am going to post my experience here!

    Now FSA have a cretenious system where they decided that the best thing for their bolt patterns to be would be three bolts in a 86BCD (bolt circle diameter) see this link for ‘advantages’ which is claimed to be better because you can get down to a 26T chain ring (because shimano have really struggled, right?).

    This proved a problem when I decided I wanted to run 1×10 on my Boardman HT Pro (which uses a bb30 bottom bracket therefore cheap cranks can not be bought anywhere!). After e-mailing FSA with my problem they suggested, helpfully, that I buy their FSA afterburner cranks with the chain rings for a delicious £260. Not going to happen.

    Another option was to buy a bottom bracket converter to something sensible like GPX, these cost ~£70 and then I would have to buy new cranks on top of that so that was also a complete NO GO.

    I also decided that I didn’t want to get a custom chainring shipped from america from warhawk industries who seem to be the only people I could find at the time.

    I then decided (being an engineering student) to make an adapter to fit one to the other, this consisted of the drawing below (just incase anyone feels brave enough to do this as well, I would read everything before you jump ahead and do it!)

    I then had this laser profile cut out from steel as no one actually cuts from aluminium apparently. The bolt holes all lined up very well and everything looked like it would run smoothly.. How wrong I was!

    Once I had aligned the 386 bolt holes I then noticed that the cranks interfered with the 104 bolt holes so I then took a file to them to make it fit. Once this fit I then thought job done!

    Wrong again. Then came the issue of trying to fit the chain ring, this required a hack saw, measuring multiple times and a file. Once cut down to size and filed properly I had to use a hammer to get the chain ring bolts, chain ring, crank and adaptor to sit together. Not a fun experience at all!

    Below are the close ups of the cranks from inside and outside, below them are the before/after of the bike.

    I personally think it looks very neat and tidy now that it has actually been fitted. It works well and doesn’t flex even a little. I have abused it around sherwood pines in the highest gear I have and stomping around the course, it is being raced tomorrow and I have every faith in it.

    If you are having a similar problem you are more than welcome to use the drawing above but I would advise against it unless you know your way around a work shop and are happy riding butchered (but completely one off and custom) bikes. If I were to do it again I think I would buy a warhawk chain ring or buy some silly cheap cranks off of ebay second hand, not quite the same though!

    Costs – £20 for the chain guide from superstar, £30 for the guide ring from e-thirteen, plate £0 (I know a guy).


    Your ingenuity is quite impressive however from a aesthetic point of view the back looks a bit of a mess and not too convince on how well the outer ring will hold looking at the amount of material cut from the chainring bolt flanges?.

    Would it have not been easier to have got some stainless steel lasercut into a actual chainring forgoing all the above as its a single ring the tooth profiles dont need to be fancy just the correct depth,thickness and pitch.

    Also the custom chainrings work out at about £26.88 plus shipping ,not a big difference to what you spent on the e-thirteen one.

    Goodwork all the same.

    £26.88 plus shipping and the wait to get it over here in the first place, it also isn’t as unique!

    The amount of material cut from the chain ring was actually a surprisingly small amount (considering it was ~1.5mm from the hole anyway), it is pretty much an interference fit with the cranks as well and is hellishly tight so definitely isn’t going anywhere any time soon (along with loctite and very very tight bolts). Aesthetically yeah, not great but it works!

    Making my own chainring out of stainless would have been more of a hassle and would have actually cost me money to get cut out, the teeth are also chamfered which would cost more (as the ethirteen one is stamped and machined not laser cut).

    Premier Icon AlexSimon

    Well done for having a crack at it yourself. Look pretty good in the photos!
    I have all these different BBs (especially as I’m stuck with BB30 on my halfords cross bike like you)

    Premier Icon woody2000

    Is this some kind of subtle astroturfing? Are warhawk[/u] rings that good? 😕

    Woody2000, I have no idea, I haven’t found anyone else who does it for the 386 pattern which is why I mentioned them, you could also go for a spiderless chainring from various other companies but would look silly if the crank arm still had the spiders on.

    edit: Havent found anyone that makes sizes between 29 and 39.

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