I put 55k on my beloved '71' CB750. It was mint condition. I kept it in tip top shape. I made memorable trips from my home in San-Diego to Kansas City and several other long distance rides.
This is the bike on which I rebuilt the shift tumbler assembly coming back from Eugene, Oregon, on the side of the road about 1/2 mile north of the Golden Gate Bridge in San Francisco, early on a beautiful Sunday morning. With nothing more than the OEM took kit and my mechanical impact driver. I've been pretty proud of myself for that operation all these years! Alas, there was no one there to witness my genius.
Isn't that always the way it goes? I later pulled the engine and split the cases to repair damage to the transmission gear cluster caused when the shift tumbler failed on that trip.
I'd purchased a Kawasaki 500 Mach III, so I sold my Honda to a young man who was very excited about doing his own maintenance. I thought it odd at the time. I've always been excited about riding the machine, not servicing it. I told him I had just gone completely through it. Valve adjustment, balanced the 4 carbs, new points adjusted perfectly. Oil change, brake adjustment, you name it. I said, 'Just take it home and ride it. Don't mess with anything.' But I had a weird feeling that my advice was falling on deaf ears.
A few days later, I got a call from the buyer. 'It's not running very well' he said. 'I dont' know what's wrong. Can you come take a look at it?
I thought, 'What in the world? Nothing runs sweeter than a 750 when it's tuned.' He didn't live far away so I headed over to his duplex.
There it was, in all of its glory, sitting in the garage. I couldn't see anything waving a red flag, so I asked him to start it up. It fired reluctantly, which was unusual, and immediately made the most horrendous clattering noise. I yelled, 'Shut it off! Shut it off! I then asked 'What did you do to it?’.
'I didn't do anything.'
'So, it just started making this noise then? When did that happen?'
'Last weekend', he replied. 'When I started it up'.
'So, you shut it down and it was fine. Then, when you started it up again, it made this noise right away?'
'Almost right away, Yes.'
The noise sounded like it was coming from the top end. So, I started there. That's when I spotted it. The CB-750 has a dual overhead cam engine.
One of the first in a production motorcycle, I believe. It used threaded, nut locked valve adjusters. The valve cover had 8 threaded cast aluminum access ports. 4 in front (Exhaust), 4 in back (Intake).
My valve cover was in much better condition than these. But you get the idea. Still, as nice as it was, the aluminum had gained a patina of sorts. That is when I noticed one of the access covers was brand new. I pointed at it and asked the obvious, 'What is this?'
'Well,' he said sheepishly. I had to get a new one.'
'What happened to the original', I asked, not sure I really wanted to know the answer.
'I was adjusting the valves and that one broke when I put it back on.'
Thinking of how many times I had adjusted the valves myself, and how much force would have been required to break one, I said, 'These are O-Ring sealed. They are just pot metal and not designed to take much force, because it is not needed.' Bringing me back to our original conversation where I implored him not to mess with anything.
Following the now glowing trail, I asked, 'What happened to the one that broke?'
'It shattered', he said.
'And what happened to the pieces?'
'Well', he stammered. 'I got all of them I could. But maybe I didn't get them all.'
'So, some of the pieces fell into the engine then...' I said rhetorically.
At that point, my dreaded suspicions became crystal clear. I stood up and said, 'Put it on a trailer and take it to the dealership. Do not start it up again. You're just making it worse.'
'So, you can't fix it?' He asked horrified.
'I could, but it's going to be a big job. You have to pull the engine to remove the valve cover. And that is going to be the necessary 1st step if this is ever going to run again.'
And that may well have been the demise of my well-loved CB-750. I don't know. I never heard from the guy again. I am, at least, grateful for that.
I know it was just a machine. But I still feel a twinge of guilt for selling my faithful friend to that guy.
) Anyhoo, there's some more good vids on youtube from this same Lady, Doodle on a Motorcycle, but this is one of just a couple she's done in Oz. Check it out: 
en.wikipedia.org
That ride was for a good cause tho, so maybe that one doesn't count?! 
