The rear brakes had helicoils inserted by a friend from work. Buying him lunch to do it for me was a much better option than spending the $50-$100 to buy the inserting tools to do the job right. In addition to the fact that I do not have a drill press to ensure the new drill hole was straight. Normally I would take the 'close enough' approach like I discussed in a previous post, but these are my brakes. So below is just an example of what an inserted helicoil looks like since I forgot to take a picture before installing them on the kart.
New O-rings:
With those new threads inserted I also decided it was time to upgrade the sealing o-rings again. You might recall that after I first drove the kart I had replaced all of the o-rings in the brake system. While the old o-rings got the job done, they were very soft and would often fail from me over-tightening them. In the world of seals soft is usually a very good feature to have, since the soft material will deform better to the surface it is being pushed up against.
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| After installation and while not in use |
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| Under normal operating conditions |
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| O-ring yielding |
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| O-ring failure |
While the above pictures don't show exactly how my o-rings might fail, it is pretty close. I decided to go with a harder material o-ring simply such that the chances of me over-tightening the bleeder screw and causing the o-ring to fail are much less likely. This might seem like a silly problem to have since the idea of over-tightening seems like one that could easily be avoided; so, I'm going to elaborate on what the problem is exactly.
The bleeder nuts are small nuts (4mm) that I have to remove to let small air bubbles out of the brakes. I have to do this almost every time I go racing. Air bubbles in the brakes mean the brakes will basically not work. The fluid in the brake system will experience upwards of 1000-2000 pound of pressure per square inch (psi) when I really push on the brakes, and the seal needs to be able to hold this force back. That means when I put these nuts back in, they need to be tight enough to ensure the seal is adequate as well as simply not fall out while racing (every part of these karts vibrate so much that nuts will often come loose). So what is too tight? Well if you recall the last time you put the cap back on bottle of soda (back on, not take off) that finger tight feeling you recall would be TOO tight and fail the o-ring. So I hope this makes you understand the dilemma I felt with these old o-rings. "2000psi" versus "looser than a bottle cap" versus "falling out".
However, with the new o-rings, I am able to exert a lot more force on the nut (a little tighter than a bottle cap now) and form a good seal. The new o-rings are a material called Viton and are pictured below. They are also much more durable. I sense that this is boring to most people, but the next time you push on your brakes really hard (or at all) imagine if they decided to stop working right then. Now stop from 100 mph in less than 100ft.
The only concern I have now, is that since I am torquing these nuts a little more than before, that I might strip the threads out of the front brakes now. If that does happen, I'll have to helicoil all of the brakes, at which point I am sure they will be more than adequate in strength. The calipers are all made of a cast aluminum which is surprisingly soft. The steel helicoil inserts can take a greater load and distribute that load over a greater area on the caliper. The front brakes failing does not concern me as much as the rear brakes, since they are more of a supplemental braking system, rather than the main. It has also already happened to me once before and I fared well. Just over heated my rear brakes a little.
Track night #3
The kart runs pretty well now. The motor delivers smooth and continuous power. There were some small modifications done at the track again. But I'll discuss technical details in the next post. For now I simply share a list of things to fix, and videos....
List of 9 items to fix:
1) Fix the radiator mounting
2) FIX THE RADIATOR MOUNTING
2) Get the front-end alignment back to near zero
3) Mount fuel pump behind seat, not right under the exhaust port
4) Provide proper vent and fuel return lines
5) Steering wheel
6) Ream out the channels on the shifting rod so that it doesn't jiggle so loosely
7) Repair radiator hose
8) Reposition the seat to actually even out the weight distribution. (57% on the back is the goal)
9) New radiator cap
Here's Ken, the guy always with me at the track, taking out an 80cc for a spin. I've got a lot to learn.
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