Foot - College Park Odyssey K2 Review and Repair.

I am a left above knee amputee. I use a hydraulic Ossur 2100 knee and a College Park K2 ankle on my prosthesis.

I bought the College Park Odyssey K2 foot on E-bay. It now leaks hydraulic fluid from where the piston comes out of the seal plate..
This blog is about the K2, and how I fixed the leaking seal. It is NOT, about how YOU, should fix or repair a leaky K2.

I have a Ossur VariFlex that was my beginner foot purchased by my medical aid. Many of the Parkruns I have been doing, are on steep slopes, and uneven terrain. The VariFlex does not handle either slopes or uneven terrain very well.

Some ankles and feet give better energy return. Some give better stability, and some give better safety on slopes and uneven terrain. The Variflex has some energy return, and feels very stable. The K2 has no energy return  that I can feel, and requires the good leg to do 100% of the balancing. It is sort of a "dead" feeling foot. But it has two good characteristics.
One is that the toe remains in full dorsi-flexion when the foot leaves the ground right before swing through. This is over a half an inch of extra toe clearance while the foot swings forward. On grass, or gravel, that is a super safety feature.
The other good feature is that if I step on a rock/root/carpet/clump of grass or any small item, with my toe, it allows the toe to go up. This prevents my knee from unlocking when the toe steps on something. It also allows the ankle to handle slopes. A 9 degree down slope can be walked as if it is level ground.
So basically the K2 is more unstable, and has no energy return, but allows slopes and uneven terrain. It also has more ground clearance during swing through.
The Variflex is a stable foot with some energy return, but does not handle slopes or uneven terrain.

After 4 months, my E-bay K2 started leaking from the piston top. So I decided to repair it.
Fortunately I was loaned a College Park Trustep for 2 weeks. After that, I had to wear my VariFlex while repairing the K2.

 This is my K2 on the work bench.

After removing the foot shell.

All K2s are both right and left. Only the foot shell determines which foot it is for. I don't like this. The main shaft of an ankle must be in the same plane as the main shaft of the knee. This means the K2 is always pidgin toed, and the weight passes over the middle toe, not the big toe.

This is how the curved piston looks on the inside.

After removing the carbon fiber foot plates.

This shows the dorsi-flexion adjustment screw, the big bolt, and the four screws for the seal plate. The big bolt needed a 3/8 thin walled socket to loosen and tighten it.

This shows how the curved piston moves.

After removing the big bold that connects the piston to the pyramid.

The end of the main shaft after removing the retaining screws.

Blue plastic protecting main shaft screw.

Main shaft screw. It locks against the main shaft, so that the shaft moves with the pyramid adapter.

Main shaft after pulling it out. You can see the grove that the shaft screw fits into.

Now top pyramid can be removed.

This allows access to the four screws holding the seal plate. These need a #7 Torx.

Seal plate removed.

Seal plate and the removed bad seal. This was where it was leaking.

Prep to remove all fluid.

Removed 4ml of old black fluid. 

Prepared 350CTS silicone oil. I put back in almost 8 ml. I totally guessed at the Viscosity of the fluid.

New purchase of seal and o'ring.

Install new seal and o'ring. Note funny path for o'ring. It has to go around the input to the adjustment screws.

Prepare and add new oil.

Seal and plate must accommodate curved piston.

Put seal plate on correctly so curved piston fits curved seal.

Put on 4 screws to hold seal plate.

The shaft needed sanding and filing. I think I messed it up getting it out.

Shaft installed and end retaining screws installed.

Big bolt installed to attache the pyramid to the curved piston. Replace main shaft retaining screw, and plastic. Then put on carbon fiber feet planks.

Foot is done. Now to put foot shell on, replace the Variflex with the K2. Then go for a walk.

I am now wearing the K2. It seems very stiff. Even with the resistances at minimum. I think the shaft is hard to turn. I did grease it with light duty grease. Maybe I messed up the brass bushing of the main shaft.
Maybe, I should have used a thinner oil.
I'll need to walk with it for a few days to see if it is usable. The K2 is heavier than the VariFlex, so I will have to adjust the resistances of the knee to allow for the greater inertia of the heavier foot.

If I have to change to thinner oil, I will have to be more careful not to damage the shaft getting it out.
Also the four #7 Torx screw heads are nearly stripped.