So, you want to learn about tribology, metalworking, and/or wire drawing? Check my ResearchGate page, many links to full-texts and DOIs there.
So, you want to learn about tribology, metalworking, and/or wire drawing? Check my ResearchGate page, many links to full-texts and DOIs there.
Apparently, I have a youtube video. I hope the ACS is making money on this!
I mentioned that I’ve been riding the Sherpa a lot lately due to a shoulder injury, and it’s been a total blast for the most part. Just not the grooved pavement part.
Last year, I fitted the little green bike with IRC TR8 tyres front and back. They are a good medium duty knob that is regarded well for its on-pavement performance and durability in addition to its very good dirt and gravel chops. I like them a lot on gravel and on grass (yes, I ride on the lawn), and find them to be pretty decent on asphalt.
Unfortunately, a large amount of Michigan seems to be grooved concrete, and knobs and grooves do not seem to get along well.
I initially played off the serious instability of the bike on the tyres being knobs, but the truth is, the TR8s are not a particularly squirmy tyre. If they were, I’d notice the issue on all roads. I finally traced it to the grooves when a colleague noted that my rear tyre was “moving around an awful lot” after following me on I696 one morning. Another day, I had a braking “incident” where I locked the rear while stopping for a red light and the little bike became extremely squirrely. I revisited that lane later and found that it was not only grooved, but the grooves were full of silt and sand. My guess is that there was just enough low traction material to keep the knobs from biting the grooves, and that led to the lockup. I rode it out and did not hit the car in front of me.
I suppose that the lightness of the Sherpa is interfering with me feeling how much the bike actually is moving under me. Apparently, I’m becoming rather used to it and no longer bothered at all by the extra motion. This is a big step forward for me as a rider – I’ve had some fear about handling low traction surfaces and now I find out that I’ve been living with an entire low traction bike for the last two months.
The role of traction* in the stability of a motorcycle is interesting. Too much at the wrong time, and you are flying over your bike in a high-side dismount. Too little and you are hitting the ground in a low-side fall. Somewhere in between (and a pretty big section of in-between, thankfully) is enough traction to stay upright and move forward. Control of the traction force is up to the rider – one can spin up the rear in a nice, smoky burnout, or manage rolling at just the right speed to keep the rear tracking around a hairpin. That burnout is a roost in dirt, where the surface determines more of the traction characteristics than the tyre does. The knobs on knobby tyres allow the tyre to dig into the surface and grip more of it, trying to catch it and lock into it. Roosting occurs when the surface is torn up and thrown into the air. Obviously, this is a bit challenging to do with concrete, so the tyre gets torn up and thrown into the air instead. You can think of the difference between street and dirt riding in terms of which surface is the primary sacrificial one – while dirt tyres do wear (and quickly!), the surface takes more of a beating than the tyre does. This is why motorbikes are often banned from outdoor recreation areas – too much damage to the trails.
Riding in a situation where the traction is not at the operator’s complete beck and call can be unsettling, at least until it is ingrained into the rider’s personal physics. The old term “backing it in” refers to breaking traction at the rear while sliding the bike around a turn. Done properly, this is a very controlled use of traction (or the lack of it) to the rider’s advantage. It requires the rider to have significant comfort in the lower traction environment. One needs to feel confident that they can successfully hook back up and ride it out, without hopping over the line on the track that leads to a high-side. Where better to learn this than on knobby tyres in the sand or loose dirt?
All of this musing here is about me coming to terms with low traction. I’m finally starting to really get a feel for it. The baby GS has great Metzler Tourance tyres on and they are profoundly stable under many conditions. Add in the bike’s rudimentary ABS (it’s fine, quit bitching), and the bike is rather insensitive to traction condition transitions that would send the Sherpa and its knobs into orbit. Me along with it, too. Logging more seat time on the little bike with its little traction is helping me understand what low traction feels like and how to not only manage it, but relax and enjoy it. I’m not sure I’m ready to slide all 425# of the Beemer around, but I find that I’m getting less and less freaked out by the wandering rear end of the Sherpa each time I get on it, and what I used to consider frightening wobbles and stepouts are now just situations that require me to moderate my control inputs. I’m thinking less about everything associated with low traction now and riding it all more. Grooved pavement is no longer a navigation avoidance parameter.
Yikes. I might actually become a decent motorcyclist one of these days.
*Traction is friction in the presence of rolling, and is related to friction by the differential speeds of the two surfaces as described by the slide/roll ratio. I’m happy to pontificate on that, it’s kind of my thing.
Everyone who knows me knows that I am a big fan of Hawk Performance brake linings. Ever since my first set of HPs pads on the B5, I’ve been running various Hawk compounds for various purposes. I usually match the compound of the brake linings to the tyres I’m running, so HPS with my winters and HP+ with my summers.
Recently, I needed to repair a leaky power steering line and in the process discovered that I had a loose pad on the front axle. Further investigation found that the lining had separated from the backing plate. This is pretty much a catastrophic failure for a brake pad, so I’m glad I caught it when I did. Considering what the car has been through, I wasn’t too upset with the situation – the car sits for longer periods of time in the summer when I don’t really drive it at all. Add in all the winter salt and who know what’s going on there.
We do some brake bonding at my employer – designing the adhesives used to hold the linings on the back plates, so I was curious to hear what Hawk had to say. I reached out through their customer service contact page. A few days later, they came back, asking for photos, which I gladly sent in. Almost immediately, the answer came back – “we can warranty those for you.”
So, I have to say, I’m pretty darn pleased with Hawk. Not only for the performance of their linings, which I really like, but also their Customer Service team, who took care of this issue. No doubt there will be some sort of work on their end and hopefully my pad set was an anomaly. It’s refreshing to know that they stand behind their product even when things go pretty wrong.
Thank you, Hawk!
Germany has a rule-based culture, and a fair chunk of life is spent figuring out how to get around the rules while still obeying them. Spirit vs letter of the law. In the US, we prize the Spirit of the Law. In Germany, it is the Letter of the Law. Once I figured this out, my life in Germany got to be fantastically easy. Just figure out how to get around the rule while creatively applying it, and you are fine. VW’s emissions control defeat programming would put the cars in compliance with the Letter of the Law, which specifies the testing conditions, while violating the Spirit of the Law, which says “don’t pollute”.
I am totally guilty of this, and I think the statute of limitations is up by now.
My wonderful MkIII Golf GT TDI (up top there) was not really in compliance with anything. It was low. It was leaky. Very leaky. And it sort of stopped. However, it was only a few hours of work away from passing the TÜV. Just like every other modified car in Germany – I had a procedure to get my car ready.
This is what it took:
When I arrived at the testing station, the car was solidly at 11cm and my coil count matched the paperwork. Braking was acceptable. I got some dirty looks for my snow tyres because it was May. I earned a comment on how clean the engine was. I noted it and realized that I should have cleaned it a week earlier to look less obvious. And the emissions check was thankfully in spec with no weirdness.
I failed on a broken reflector lens.
When I went back two weeks later, the lens was all they could check. So my clearly leaking (it was dripping) and obviously too low Golf was cleared for driving, because I passed the test as it was written.
I feel kind of funny saying this, but the “pass the test as written” is a cultural thing. With regard to #Dieselgate, I am willing to bet all of Internal Combustion knew exactly what was up and didn’t really think it was that big of a deal, because they passed the test. Oops.
Time to bust out the old sonicator – a 1960s Narda SonBlaster 600 that my dad trashpicked about 35 years ago. It’s still going 60W strong. One of the cooler features is a limited tuning function that allows you to max the coupling constant for a given group of parts. It has two tanks and will drive one at a time.
The carb parts cleaned up very nicely in a 40/60 mix of Simple Green and water.
Although I ordered up some new jets for it, I likely won’t use them. The OE ones are in good shape, and I’d rather re-jet for a slightly richer mix.
The culprit was the air filter – it had a bad day. As far as I can tell, the mess is limited to the intake horn and the carb. I’ll get out the boroscope to check the intake valves tonight. And try to find a new air filter. A paper one would be better, I hate foam filters for exactly this reason.
My Sherpa decided to no longer fire. I was getting air and spark, but possibly no fuel. Petcock (what magic is this vacuum thing?) is ok.
This little Mikuni is not an SU. Or a Holley. Or a Weber, or a Stromberg, or any other carb I am familiar with.
Slide diaphragm is ok…
Hmmm, was that my air filter?
More to come.
The 11mm Brembo master cylinder fitted to the rear braking system on many Aprilia, BMW, and KTM motorcycles is a weak point, to put it mildly. Regardless, it is fixable. See below for how and why.
0. Tools required
Inside circlip pliers
5mm hex drive
2mm long drift (10cm) or 2mm Allen wrench
Dremel with small round cutting bit
One full rebuild kit from Brembo, part number 110.4362.41
1. Remove the master cylinder from the bike. To do this, remove the bolt holding the brake fluid reservoir and washer with a 10mm socket. Return the bolt and washer to the hole to insure they are not lost. Drain the reservoir and replace the lid and gasket. Release the brake line fitting from the top of the master cylinder and back it out entirely. Remove the two bolts securing the MC to the bike using a 5mm hex drive. Lift the MC away from the bike, clearing the brake line at the top. The push rod will slide out of the rubber boot at the bottom with a slight tug. Return the two hex screws to the bike for safekeeping.
2. Retire to somewhere warm (or cool…), you might be there for a while. Bring the MC with you. Spread some paper towels or other protection out, and drain the master cylinder fully. Set aside the rebuild kit for later.
3. Carefully examine the MC. Remove the rubber boot by tugging at it gently. To help it, insert a flat screwdriver into the groove at the base of the MC and gently prise the boot away. Looking down the bore of the MC, you will see the piston at the center, a white spacer surrounding the piston, and a circlip holding it all together. The circlip may be rusty, if it is, you have some work on your hands. See below for a good (bad) example of a rusty circlip.
4. Remove the circlip using inside ring removing pliers. If the piston is stuck, use a long 2mm drift or a 2mm Allen wrench to drive it out from the top side. Tap the drift or the Allen key gently with a tack hammer, checking the other end for progress occasionally. When approximately 4mm of piston are exposed, gently grab the piston with long nose pliers and slide it out. This will all require some effort. The spring and spring seat will also come out at this time, or can be shaken out gently. Examine the piston for corrosion and clean it.
5. Now for the fun. The white sleeve may not slide out willingly. If it did, you would not likely be attempting this repair. A rather easy way to remove the sleeve is to grind or cut a groove in it. I used a 2mm ball-shaped cutting bit on my Dremel and ground out two channels, one the full length of the sleeve. Using the circlip pliers, twist the sleeve in the MC body and slowly work it out. Another way to remove the sleeve is to turn the bits of a 90° circlip tool to the outside and use it as a puller. In either case, take care not to damage the surface of the bore. It is not a sealing surface, but smooth is very important to the cylinder staying functional for any length of time. After removing the white sleeve, remove the o-ring that is still in the bore.
6. Once the white sleeve is removed, you will have to clean the inside of the outer bore where the sleeve was sitting. If the circlip was rusty, you will likely also find rust inside of the bore. Using Scotchbrite, steel wool, or very fine sandpaper, remove the red rust from the bore. Clean the bore to remove the residue from this round of cleaning.
7. This step is critical to determining whether the MC is going to be repairable for any length of time. After the red rust is removed, use a pick to investigate the condition of the outer bore. If you have tiny fingers, they will work, too. Now, you are looking for corrosion of the aluminium cylinder body. This is the corrosion that is causing the piston to stick, not the red rust. Using a pick, gently flake away any aluminium oxide that has built up in the bore. Under the oxide will be pits. There is no getting around this. Fortunately, these pits do not interfere with the operation of the cylinder if they are properly treated prior to reassembly. This process is slow and time-consuming, but will pay off in the end. When you have removed the fluffy stuff, carefully clean the entire MC and the reservoir and feed line. Blow them out well with clean water and air, and dry thoroughly.
8. When you have removed the aluminium oxide from the bore, it is time to open up the rebuild kit and start putting things back together. Remove the white sleeve from the kit and test fit it to the bore. It should float smoothly in the bore with only very slight resistance to turning or sliding. This indicates that the bore is free of oxide. Remove the white sleeve, and coat the inside of the bore with Loctite Silver or Heavy Duty (black) antiseize. Do not use copper-based antiseize! This coating should be very very light. Coat the new o-ring with brake assembly grease (HMW polyoxyethylene, supplied in the kit) and insert it into the bore. Insert the white sleeve and twist it gently in the bore. Assemble the spring to its spring seat, and slide the spring into the bore. Coat the piston and seal with brake assembly grease and insert them into the bore. The piston will stick out a bit.
9. To finish the assembly, fit the new circlip to the inside circlip pliers. Secure the master cylinder body and hold the circlip over the piston. Using a suitable drift, inserted through the center of the circlip, depress the piston into the MC, and secure the circlip. Treat the circlip with a drop of wicking grade low-strength threadlocker and, using a pick, draw the threadlocker around the circlip to coat it evenly.
10. Bench bleed the MC and install it to the motorbike, in reverse order of removal. Fully bleed the braking system, including at least one ABS activation in the middle of the process.
Conclusion: The boot on the MC is poorly designed and encourages water to enter the space within the boot. Basically, the boot should be inserted into the MC, not sitting on the outside. This moisture leads to corrosion of the circlip. However, corrosion of the circlip is not the reason the whole thing fails, it is just part of a chain reaction of fail. Once the iron starts to go, it triggers a galvanic reaction in the aluminium and the aluminium begins to corrode. The problem is that aluminium oxide is fluffy. Very fluffy. And very incompressibly crystalline. This increase in volume puts pressure on the white sleeve and eventually causes the piston to bind.
My fix: Forget grease. It won’t hold up. Use a heavy duty anti-seize product like Loctite Silver or Heavy Duty (black) to fill the void between the sleeve and bore, and then coat the circlip with low-strength (green) wicking threadlocker, which is commonly used as an anti-corrosive coating on automotive fasteners. If you are in Aviation and have access to Alodine 1424 or the like, a coating of this on the inside of the sleeve bore (along with overnight drying) will also go a long way to preventing repeat performances.
I rode out to Kalkar Mill on Saturday afternoon to check out the stones. Kalkarermühle is an operating windmill in Kalkar, NRW, Germany, and home to a diverse bunch of people who have decided to keep the windmilling trade alive as volunteer millers. One of the millers is a friend and fellow rider, and introduced me to this neat old technology last fall.
The key to the mill is the stone set. The lower stone, shown here, is fixed and does not move. The upper stone is supported on a pintle that is driven by the familiar sails that catch the wind and power the operation. The entire rig runs at around 120rpm, which is quite speedy, considering that the stones are about 1.6m in diameter. That comes to an edge speed of 24m/s! When the season for milling is low (winter), the millers open the stones for cleaning, resurfacing, and rhynd repairs. On this stone, the darker areas are the wear surfaces, and the grooves are the feeders that feed the grain in.