Im clearly no mechanic, but I occasionally try. Here’s my 3 worst basic mistakes (worst first)
Changing brake pads - took new ones out of the box, took the old ones out of the bike, installed the old ones, threw the new ones away. Even tried to bed in the old ones! Sadly the new ones have gone before I realised.
Removed brand new bike from its box, carefully unpacked bit by bit. Cutting lots of cable ties whilst also cutting the Di2 cable connecting seat post and tube.
Installing a chain and threading it round the cage onto the metal pin, not the pulley wheels, so the chain is very noisy. Then doing it again with the next chain 9m later.
Trying to screw left BSA BB cup on the right side of the bike (or maybe the contrary). Hopefully remembered that “if you use force where you need not, you’re probably doing it wrong” before ruining BB threads on the frame.
Not setting BB preload correctly on a Rotor crankset, ending a ride with left crank arm nearly of the axle
Took airspring out of suspension fork without removing air first. The c-clip was way harder to get out and i couldnt figure out why, so i just used extra force. Lucky for me the fork was upside down in a vice when 120psi shot the shaft out of the fork. It ricocheted off the roof of the garage. I was replacing the airspring so it didnt matter that it got scratched up. I got a face full of oil and a reminder why you wear eye protection during shock service.
I had a customer use Flex Seal as tubeless sealant and couldn’t understand why he couldn’t get air in the valve after about 20 minutes. Needless to say he needed a new wheelset and a lesson on proper tubeless sealant.
This is last century, 1979. I’m 13 and had to glue the tire for the first time. Asked an older teammate how to do it. He says spin the wheel hard, pour the glue on the rim, done.
I spin the wheel as instructed, hard, start pouring the glue and spray it on the wall, ceiling, floor, my shoes, legs. You get the picture.
Mechanic was sitting at the bench 2 meters from me, facing away and not paying attention to what was going on (2 minutes before, I actually asked him to glue the tire and he said, time to learn it, kid). He turns around to see wtf is going on (at this point, 15-18 boys were laughing their heads off). He starts yelling, just pure swearing, not a single normal word (you can do that in Russian). I thought he was going to smash my head with a hammer (it was right there on the bench).
The coach runs in from his room, sees the mess and starts yelling too (without searing, he’s a couch after all).
This is how I learned how to glue a tire. Those glue streaks were still on the wall and the ceiling when I left that cycling school 4 years later.
Once decided to disassemble a warrantied frameset with a 3/8” impact wrench. At some point I accidentally flipped the switch to tighten and went to remove the stem. The first setting on this impact is 30 ft lb (40.67 nm if you use catholic units). Luckily this was a frame destined for the garbage but I had to replace the stem as a result. Oddly enough the steerer tube appeared to have zero cracks or damage as a result.
I’ve built up a number of bikes, and I’ve been a mechanic in motorsports for most all my life. With that said, I had just bought an S-Works Tarmac, brought it home, put it in the work stand clamping the seat post. Things were going just fine, bottom bracket installed, crank in, DI2 wires run, FD and RD on. Decided to call it a night and finish the next day.
Now, I should explain that I have a folding sort of tripod work stand from Park Tool that I’ve had since I got into cycling, and I was working in a two car garage in the empty space after one car was backed into the driveway. When finishing for the night, I just scoot the stand back to the other side, pull the car back in and shut the garage door.
So, I scoot the work stand over with the Tarmac still in it, and take my other bike I was pulling the parts off of (Cervelo S5 Disc) and put it underneath the Tarmac I’m building in the work stand.
I go to walk in the house, take one last look at the progress I had made before turning the lights off, annnnnnd CRUNCH. The Tarmac falls chainring first straight down in to the top tube of my S5 putting a lovely hole in it. Apparently my dumb ass didn’t check the the seatpost was tight before I put the frameset in the work stand.
I road my bike in damp, but not overly wet conditions and the front steering felt sandy after the ride. I decided to attempt my first ever maintenance job on my brand new Aethos. After congratulating myself for not buying a bike with an integrated front end, and thinking about all the money I would save by servicing the bike myself and not going to a mechanic, I watched numerous YouTube videos on servicing headset bearings and got to work. Each video said it would take 10 min and took care to mention how little torque should be applied to the expander plug. It some how took me an hour to finish everything, and just as I was finishing I noticed that the expander plug was not tightening because I had over torqued it and cracked it.
The next morning I went to a shop to get a new plug installed.
Years ago, had a creak in BB area and read horrible online stories of pressfit and carbon. Clean. Inspect. Under load at certain pedal stroke. Nipped up same crank arm bolt twice* (Shimano 9100), chainrings, pedals, cleats. Lube. Test ride still there, ah well 'these press fit bb’s in carbon frames. Need a new one. It’s creaking bad. Real bad like I need Loctite 609 bearing retainer to fill the slop. And primer from a specialist shop an hour’s drive away. Then need to source bb removal tool. Order new bb express. Wait. Receive. Paint* BB cups. Press in. Wait 24hrs for Loctite curing. Need to ride. Curse brands and designs. Work pedantically and think of riding all evening, Sleep. Sun up, new day. Here we go. Bikes done. Clip in moods good. WTF, still noisy! Chuck a hissy, throw bike like Wiggins. Slightly bend rear derailleur which stays slightly that way untill hanger adjuster tool is purchased years later. anyway long story shorter. After close(r) inspection it was a damaged left crank arm from 1 bolt not being torqued correctly. ie (Very slightly way loose).Fit new washer, grease and exceed previous values. Fixed. ~ That frames bb just had a divorce from itself. Was so well glued the inner races & bearings sheared from outer races. Scarf is what remains of the bb outer shells. Air tool die grinder and a carefull hour with hand tools. I haven’t Loctited a PFBB again. Yet. I’ve just put the old BB back in with grease. Full circle. Money , time and tools.
Off topic but still 2 wheels. My dirtbike stopped & wouldn’t start again after parked in shed. I’ve ripped it apart, fuel tank, shrouds, seat off. carburettor and jets , air filter, spark lead n plug. Was about to take head off cylinder. Nuts and bolts everywhere. Double check list before it gets large. All that to diagnose i’ve run out of fuel. Was on reserve tap from last time and I’d just* filled her up. Time flies when your having fun. I’ve idled all my fuel rolling down a hill and evaporated remants in line on a hot day after lunch. Me good mechanic.