I had an exhaust issue only yesterday. Had a half completed exhaust system under the car including a $200 oval shaped stainless muffler before the diff. Only needed the pipe over the diff and out the back finished. Put the car on the trailer to take it to the exhaust shop for finishing and on the 16km trip into town the $200 muffler decided it was time to part company. I remember that I never tightened the clamp bolt. Bugger..!!
$345 later I have a new stainless muffler under the car...and the exhaust is finished.

I left one of those big dolphin torches in my engine bay one night, drove of the next day and my engine started making this horrendous noise - and I've snapped two crankshafts in my time and this noise was far worse.

Anyway the torch got wedged between the fan belt and the alternator, so the fan belt melted the plastic and spat it all over the place with a bit of battery acid mixed in, while the little alternator fan blades chopped the other half up - man I've never seen such a mess. The worst bit was that where I pulled up was out the front of a service station - and the mechanics all came out. Why do things like that always happen in front of people who know what they are doing??

Still find bit's and pieces from that 'incident' around the engine bay and it happened over 5 years ago.

Well this a good one although not done by me, I swear it is true as I saw the remains.
We had a 23 year old apprentice at the last dealership that I worked at,now this bloke started his "career"in the industry as a car detailer.We all watched him one day check wheel nuts on a car 11 times during the course of his day.
He actually did not do the modification to the car but his old man did and he thought it was well done.
So this young guy bought himself a 1 litre Suzuki ute (Indian built Maruti) now these things were a real povo pack they came with nothing so the old man decided to fit a cigarette lighter, this brainiac ran wires direct from the coil to his 2 dollar supercheap lighter kit and the day after he lit his first smoke with it, it was towed to work with the car as a burnt out wreck apparently the high side of the coil puts out approx 80,000 volts.
The rear taillights did survive.
Cheers Ade

I remeber another one...in a rush I was taking my race coupe ( the deceased white one ) to John Taylors for the suspension to be built. I was blocking my street with my car and trailer while I had to push the car onto the trailer. Maenwhile there were 2 or 3 cars each side which I have now blocked. So after getting the car onto the the trailer I decided to just whack the handbrake on and move the trailer...Well the car rolled back off the trailer when I went to move it and got stuck on the exhaust.
I then got a few people to help me lift the car back on the trailer. After much effort and tying it down, I took off for Penrith. On the great Western Hwy, this guy in a BMW X5 rolls his window down and said that my windscreen launched off the car at 90kph (in peak hour traffic) did a couple loops in the air and scattered all the traffic behind me. He said it was all OK no-one got killed and I progressed on as is nothing happened.
The next day I went back with Teretonga to see if I could salvage the windscreen but she was a gonner.

Teretonga you have a classic story to tell, I think it happened that very night when with took the A series N10 Truple SSS Pulsar off to Ansell Park for a Khanacross.

did valve stem seals on the a-12 and blocked the oil feed to the rockers, seized them and bent valves

rebuilt my a-14 but starter was bad so towed it, had no oil pressure and bang new motor seized

sorted out that starter and bearings, car had a big miss checked cam timing, changed plugs, leads, point, dizzy cap to find i had the wrong firing order

changed oil and left out sump plug 5l later i had oil

never tightened wheel studs enough and wheel came off

I don't remember what I was doing to the front end, but I too drove off with out tightening the front lug nuts.
Drove about 10 miles on a windy section of road before I heard a lot of noise and found my lug nuts loose. I had no tools, no cell. This was supposed to be a quick trip around the block. I did manage to find an old vernier caliper in the trunk that I tried to use to tighten the nuts. They would hold for about 1/4 mile.
This went on for about an hour so I could get close enough to a hardware store in a nearby town.
Didn't make it. Front wheel fell off. Lug nuts were sitting in the road behind me, evenly spaced.

Had problems a while back with the engine not idling. I checked everything 10 times. I finally got so pissed off I ripped the head off the engine to see what the f^ck was going on.
Found nothing
Finally found a blown fuse. The little bastard that's hidden in the engine harness that feeds the electric choke...
and the anti-dieseling solenoid

Me and tony, the other 1st year apprentice had been told to get the freshly recond engine of a corona up and running.
Plenty of cranking, not much firing......"pour some fuel down the carby mate, that'll get her going"..... still no luck..... better check for spark. Unfortunatley tony had been a sloppy priming the carby, so as soon as he pulled the plug lead off and I cranked it, whoooof, up she went.

Took a long time to clean all of the pink powder out of the carby after we put the fire out!!!!

(1) When I bought the ute, the tray had more rust than solid metal due to the previous owner storing grass clippings in the tray for goodness knows how long. My solution was to grind out the whole tray and replace it with a sheet of 1.9 mm steel checker plate. Spent ages cutting the sheet to fit nice and snug and had a mate MIG weld around the edges to seal it all up. Did a great job too. About 15 months later I noticed the cross beam above tha axle hanging down at a weird angle. Seems that from the constant suspension pounding the shocker had caused the cross beam to weaken and break. Seems the factory had spot welded the beam to the tray floor for a very good reason. After welding the beam together again with some angle iron for strength and then welding it to the tray floor, problem solved.

(2)I'm not very mechanically minded and had to replace the diff centre as three of the crown wheel teeth had sheared off. Did the job perfectly all by myself and felt pretty good about it too. Went to show off to my mechanic mate and on the way home felt the back of the ute swaying around real badly. Checked the back wheels and found that I had forgotten to tighten one set of wheel nuts. Only one nut left on the wheel and that was only held on by one turn on the thread. Couldn't find the other three nuts and had to call the wife to rescue me as the wheel brace was back in the garage.

There are probably several other stupid things I've done over the years but I think I've read about most of them in this thread.

Remembered another one today. Once I had finished putting the new A14 in and began filling it with water it starting pi-ssing out between the head and the manifold. Hell whats wrong with it, tighten it further to no avail. Took the mainifold off after using bad language for the last half hour only to realise the gasket that came with the rebuild kit didnt have provision for the water heated manifold galleries DUH. Didnt even think about it at the time especially considering it was 11 at night and I just wanted to get the thing running.

Heres another good one not by me but someone my dad new some thirty odd years ago. This fella was changing a diff centre over and accidently put it in upside down. Dad said this is the type of bloke that if something can go wrong for him it will. Then dad said he went to reverse out of the garage only to have it lurch forward. Then realising what he had done decided to take it for a spin anyway. All forward gears were reverse and reverse was forwards. Dad said he was ripping along the road at 60mph in fourth. REVERSE. ha ha

I had the interesting situation a few years back during a rally - We (me & my co-driver) missed the marker for a turn down into a gully & ended up getting to the bottom the fast way ie/ airborne. Car stalled & unbeknownst to us the fuel line had disconnected & the fuel pump was still going flat biscuit!
Of course we were cranking the car over to get it re-started & there must've been a spark somewhere because the whole engine bay turned into a fireball.
Yes, it did singe my eyebrows & no, I haven't seen anyone get out of a racing harness quicker since.