386 to a standard 4 bolt adapter - FSA crank woes

Unfortunately my bike (Boardman HT Pro) came with a set of FSA BB30 cranks where the bolt pattern is in a 86mm BCD and has only 3 bolts, thus meaning they get your repeated business by using this propriety bolt standard.

Before any alterations

When I wanted to change from a 2x system to a 1x system there are no rings available (apart from a company called warhawk industries in the US). So I set about designing and prototyping a conversion and the blow drawing is what I came up with. In order to avoid doing torsion calculations I had it made out of steel and a lot thicker than a chain ring (meaning it should stand up if the rings are only aluminium).

It was a nice idea, in theory, but unfortunately had to have some adjustment to both chainring and crank. The crank adjustment involved filing the tabs down to be able to fit a chain ring bolt through the plate. The adjustment to the chain rings involved a hacksaw and a bit of filing to get it to fit around the tabs. As you can see below it worked out surprisingly well. 

Getting it onto the bike after that was easy and the chain line was perfect (as it was the difference of the two chain rings) but did mean that the chain guide show in the picture below did need some alterations to get it to sit properly.

It worked pretty well for quite a few races but the chain kept dropping on both the inside and outside which is more than likely due to shoddy chain guide than anything that I had put together.

This all happened in May-June of 2013 and has now been replaced with a set of cranks that have a standard bolt pattern and a narrow wide ring which works much better and is yet to drop a chain.

If you fancy having a bash at this yourself I can hapily send you the DXF file over to get it cut at the laser cutters.