And this is the drive ready for repair:
Replacement crank arms can be ordered from Hobie and usually come with the pedal attached (LH or RH). However I had read of this happening multiple times to people on the Hobie forums and so was cautious of it happening again. There are apparently also solid aluminium cranks available in the USA but these use a standard bicycle pedal and would take a while to source. So I thought I’d have a go at making my own replacement crank out of stainless steel. This was also inspired by a mod that Josh (Yakass) did on the mirage drive for his AI (which I spoke to him about).
So here is a guide to replacing your aluminium pedal crank arms with new stainless steel ones.
The first step was to pull the cranks off the mirage drive by undoing the main bolt on each side using a 9/16 spanner.
Once the broken crank was off it was pretty evident that a crack had developed along one side of the hole over time. This had finally let go under relatively mild exertion, although it had been used pretty hard in the past. There was also quite a bit of surface corrosion evident around this area (where the setting lock pin goes through). This area of the drive gets wet and will collect salt water. I admit I haven’t washed it in fresh anywhere near as much as I should, but the amount of corrosion was still surprising. The other key issue affecting corrosion is that at this point there are two dissimilar metals in contact (stainless steel and aluminium), which would hasten the corrosion of the AL. I’m hoping that going to an all S/S system will reduce the propensity for corrosion in this area.
The same removal process was repeated for the second crank:
With the creanks free the next step is to remove the adjustment locking pin and plastic lever. This is done by unscrewing the threaded pin through the end of the adjustment pin using a small allen key. With the threaded pin nearly removed the adjustment pin and plastic level will slide down and off the crank.
Next the pedals are removed by removing the plastic end cap and then undoing the nyloc nut from the end of the shaft. There is also an allen ky bolt on the plastic cap covering the top of the crank that comes off to release the small bungee attached to the pedal (newer models only). With these out of the way the pedal will slide off the shaft. This pedal shaft is approx 12mm diameter and goes through a 12mm hole in one side of the crank arm. The shaft reduces in diameter at the end and then goes through a smaller hole in the other side of the crank. The shaft is retained by punching the end to lock it into the smaller hole. The allen key bolt in the top of the crank also helps retain it on newer models (older drives appear to have a separate side pin). The pedal shafts and holes in the crank arm are shown below:
Once this is done your cranks and pedals will be in pieces ready to make the new crank arms.
For the stainless steel material I purchased 3 metres of 19x19x1.2mm 316 Stainless steel square tube. This cost me $35 cash and is enough to make around 8 crank arms. The next step is to cut the stainless tube to length and then mark, punch and drill all the new holes required. I found this part the hardest as drilling the larger holes (12mm) was very difficult with a hand drill. Through a bit of perseverance and advice I found that drilling at slow speed and stepping up drill sizes gradually got the holes done. With the holes drilled the pedal cranks are ready for reassembly:
The process for reassembly naturally follows the dismantling process in reverse. Be careful which way the locking pins and plastic levers go on as it can be confusing. You may also need to chamfer the bottoms of the crank arms where they go into the drive to allow for a bit of adjustment.
Here is the drive finally reassembled next to the standard V2 drive i borrowed from Steve (crazychenski). You will note that I have made my new S/S crank arms about and inch longer than standard. I will try this out and if its no good then I can always cut back and re-drill.
I haven’t tested it yet so am still not sure how the S/S arms will hold up to the load. The original Al arms were a bit thicker walled tube at 3mm. However I expect the S/S will be strong enough and more resistant to corrosion. Weight difference between the two drives is negligible.
I also plan to make up a kit to replace a crank arm on the water if it happens to fail. This will consist of a spare arm that already has a pedal attached (too hard to change this on the water) along with a 9/16 spanner and small allen key taped to it. This will be permanently stored in the hull along with first aide kit, spare clothes etc in a dry bag. So that’s ti. If anyone has any questions let me know. I’ll also update on how it performs.
Shane.
