Tuesday, August 27, 2013

Stuck Forks on a V65 Magna -- How to do fork seals CORRECTLY

The V65 Magna has traditional forks, with a decidedly non-traditional internal design. Most of the forks I've worked on, when you remove the bottom allen bolt, the lower easily slides off of the tube. No fuss at all.

The V65 on the other hand, is designed differently. There's a lower bushing attached to the bottom of the fork tube. This bushing's outer diameter is the same as the inner diameter of the fork lower. The upper bushing is attached to the top of the fork upper, and the inner diameter of this bushing is the same as the outer diameter of the fork tube itself. In this manner, the fork slider moves up and down with precision, and no side-to-side slop.

The drawback of this design is that the bushing on the bottom of the fork tube has a larger OD than the ID of the bushing at the top of the lower. Which means if you need to separate the fork lower and fork tube, the fork seal has to be removed as well. Normally this isn't too terribly difficult. After removing the oil and the top cap (so you're not fighting air pressure), use the fork lower as a slide-hammer. Slide it down sharply once or twice, and the fork lower will pop right off, leaving the fork seal and two bushings attached to the fork tube.

In theory, at least. Every now and then, you'll encounter problems. My problems stemmed from aftermarket seals which were slightly too large. When I replaced my fork seals last, the fork seals were really, really difficult to install. I used a piece of PVC , and stacked two old seals on top of the new seal, and then beat the crap out of the PVC with a 4 lb sledge. Took lots of hammering to get them in. Well, apparently all that hammering distorted the seal -- or they were just crap to begin with, because they started leaking immediately.

I'm here to tell you, if you experience this ever, STOP, and do not install that seal. If it's too difficult to install, there's a problem. And if you continue installing, the problem is going to get way, way worse. Because that slide-hammer action doesn't work very well at all when the seal is stuck in there really good. In fact, what happens is as you slide-hammer, the lower bushing expands the bottom of the upper bushing. The upper bushing has nowhere to go, because it fits tightly into the top of the fork lower. Expanding the bottom of the upper bushing wedges the bushing in place extremely firmly. No amount of slide-hammering will get the forks apart.

If this happens to you, use a PROPANE torch, and apply heat to the fork lower. You'll need something bigger than the small pencil tipped torches used for plumbing work. You'll need a brush-clearing torch with a big tip.  I used this:
I heated the crap out of the top of the fork lower, and then after two big slide hammers (wear welding gloves  to grasp the lowers without burning yourself) the left lower popped right off. The right side needed much more heat, and instead the tube expanded enough that the lower race was able to pull right through the upper race. This required using a 4 lb sledge to tap the fork lower off, though. Slide-hammer wasn't enough.

This is what the bushings on the left fork looked like. You can clearly see how the lower bushing is jammed into the upper bushing.

BE CAREFUL. When aluminum is hot it's malleable, and you can easily, easily damage the aluminum with a mallet. You can actually overheat the aluminum, but it requires a LOT of propane heat. Or just a little oxy-acetelyne heat. Which is why I used propane.

Once forks are removed in this manner, you're going to have to take apart the fork tubes as well. There are little plastic (pvc maybe?) bushings on the damping rod, and there's a good chance you may have melted them. Replace if they're damaged, and clean out any melty bits you find. 

When reassembling the forks, I test fitted everything this time. The upper bushing fit very tightly in the fork lower, so I took some sand paper and sanded off the layer of corrosion, dirt, grime, and muck there. I did the same for the fork seal area. I didn't remove metal, just the muck and nastiness and powdery corrosion. 

This time, instead of using PVC, I purchased an actual fork seal driver. I first used it to tap the upper race into place, and then to tap the seal into place. It took almost no force to install this time, and my OEM seals haven't leaked a drop.  The driver is also very nice because you can leave the fork tube installed in the triple tree. This is what it looks like: 

I will never install seals without a properly sized driver again. The tool was $25 and it was SO easy to use, it made the job almost pleasant. 

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