In July 2015, I decided to restore a 1976 Honda CB750F Supersport that had been sitting untouched since 1983. At the time, I had no idea what state the bike was in, except for the fact that the gas tank was missing, the tires were flat, and the brake levers were hard to move. I had never worked on an internal combustion vehicle before, but I had just finished my mechanical engineering degree, I had 3.5 years of experience as an amateur machinist, and I had an intuition for fixing things. With 26,734 miles on the odometer, I got to work.
I didn’t know what work would be needed, so my approach was to just take everything apart, clean it, test the function of every system, and fix problems as they came up.
Spark Plug Problems – Honda CB750F
One major problem I had was with the spark plugs. In the process of disassembling the bike, one of the plugs was so old that it just shattered as I tried to unscrew it with a wrench, so the threads were stuck in the engine head.
After removing the engine from the bike, I drilled out the old plug and used a TimeSert spark plug insert kit to re-tap the hole and install a solid-walled, copper-plated steel threaded insert.
Unfortunately, after the whole bike was rebuilt and I was ready to start it, I accidentally cross-threaded one of the other spark plug holes, which I attributed to the softness of the aluminum head and CTE mismatch relative to the steel spark plug threads. At this point I decided to just put inserts in all four cylinders to prevent this from happening again.
Rather than taking the engine apart again, I removed it from the bike and flipped it upside down. Then I re-tapped the holes with thick grease filled into the flutes of the tap. The grease caught a lot of the chips, and any that made it into the combustion chamber I blew out with compressed air. I pressed a thin, flexible plastic tube onto the end of the compressed air nozzle so I could reach deep into the chamber to blow out all the chips through the spark plug hole. This worked pretty well.
Summary of Work Done – Honda CB750F
The entire project took me two months full-time to complete. I completely disassembled, cleaned, and fixed every part of the bike except for the crankcase, which I did not open. The work included the following:
Engine Top-End Rebuild
- Cleaned valves
- Re-ground valve seats
- Polished inside of combustion chambers
- Cleaned/polished head gasket and base gasket interfaces
- Replaced head gasket and base gasket
- Replaced miscellaneous other seals in the top end of the engine
- Honed the cylinders
- Cleaned and polished the pistons and combustion chambers in the head
- Replaced the piston rings
- Checked the timing chain tension and tensioner
- Installed copper-plated steel threaded inserts in all four spark plug holes
- Adjusted the valve tappet clearances
Miscellaneous
- Disassembled, cleaned, replaced jets, and replaced seals in all four carburetors
- Polished exhaust pipes
- Replaced exhaust header gaskets
- Cleaned the air box and replaced the air filter (I kept the stock air box)
- Checked the drive chain stretch and wound up just soaking/cleaning it and lubricating it
- Filed the ignition points and set the gaps
- Set the ignition timing using a timing light
- Replaced the clutch cable
- Replaced the front break caliper and piston (the old one was irreparably frozen)
- Unfroze and cleaned the rear break caliper pistons and replaced the piston seal
- Replaced all the rubber break lines with steel braided hoses
- Rebuilt the front and rear brake master cylinders using rebuild kits (springs, pistons, seals, etc.)
- Installed new brake pads, but kept the original rotors
- Cleaned and polished both wheels
- Had new tires put on
- Greased the swing arm
- Replaced the battery
- Installed a momentary switch in the right hand control to replace the original broken starter button, and sealed it with hot glue
- Disassembled, cleaned, and rebuilt the forks with new seals and oil (I kept the original springs)
- Changed the oil and oil filter
- Replaced the ignition coils, cut and spliced new wires, and installed new spark plug caps (with internal noise filters)
- Bought a used gas tank, cleaned the rust out of the inside, installed a new petcock, and painted the tank with a spray paint color from Advance Auto Parts that was close to the original color
- Painted the side covers to match the tank
- Installed an aftermarket fairing that came with the bike
When all was said and done, the bike ran great! I put about 3,300 miles on it over two summers then sold it, and I was on to the next project. §