Motobecane Rebuild

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So you bought a Motobecane

These steps are all bare-bones "complete before running" steps. Skip them and experience eventual misery.

Complete Rebuild

  1. Buy a dremel, a basic sanding kit, this puller set, a timing micrometer, a fairly comprehensive set of tools, gasket paper, and razor blades.
    • You will need all the pullers in that set eventually, and it's cheaper than buying MBK-specific pullers.
    • If you don't have a timing micrometer, you can use an automotive length plug with the electrode cut off, but that's advanced technique.
  2. Clean everything. Remove rust. Check structural integrity. Check for rubber rot on belt, tires, and fuel lines.
  3. Replace ALL rotted rubber components. Get an Ax29 belt off McMaster or your local auto parts place.
  4. Remove any and all rust from the gas tank. There are many methods, but some acid and a good number of rinse cycles work well. Replace the petcock and fit it with a fuel filter and fresh fuel line.
  5. Replace your motor mounts. This is essential. Energy Suspension bushings from the auto parts store work well if you press a steel core into them. Chisel out the old rubber from the steel shell and finish with a dremel sanding wheel. It will stink.
  6. Remove the Novi nut. Use a piston stop or some rope down the spark plug hole. Remove the novi nut by turning it clockwise. It will be seized and/or stripped. Use your dremel to slice off a lobe of the soft steel and knock it loose with a drift/mallet. Screw extractors won't work, unless you can find a big one with a left hand twist. Replace with a reverse thread flywheel nut or experience sadness.
  7. Disassemble your engine. Split the cases and remove the crank and bearings. Remove all gasket material. Replace case seals and bearings. Rebuild with fresh gaskets. Now is a great time to case match. Lap the mating surfaces of the head and cylinder on a piece of granite tile or a piece of plate glass until you've removed all surface imperfections. Surfaces should be totally flat.
  8. Replace your piston rings and check your stock cylinder bore for carbon. Remember to clean the piston ring grooves.
  9. Replace points, condenser, spark plug wire, boot, and plug. Do it now before you catch Motobecane Disease.
    • Alternatively, get a Le Partie CDI and achieve instant nirvana. Best $75 you'll ever spend.
  10. Rip the entire stock wiring harness out. Every single wire. Keeping old wires are not worth the headache. Rewire with a common 12V rail up to the headlight, back to the tail light, and switched through the brake light switches. Spend the extra money and get some decent crimp connectors.
  11. Replace your headlight with a 55 watt unit. Replace the taillight with an LED unit. Do not skimp on this one. The stock headlight is an 18 Watt unit from before the invention of the HID. You want to be noticed by the drivers out there (just ask my right knee).
  12. Clean out your Blunderbuss and pop in a new copper crush gasket.
  13. Replace every cable. Even if they "look okay". I've had too many brake cables pop in the middle of a ride to skip that one. Do the decomp and choke cables too.
  14. Test and replace your brake shoes. Clean any rust from the drums. Clean and grease your bearings. You'll need a cone wrench for pre-1979 models, though even the 1979 models have loose bearings front wheels.
  15. Disassemble and grease your forks, they're all that stand between you and potholes.
  16. Grease your variator, and driven pulley lightly.
  17. Your pedals are likely bent. Either pound them out or replace with pegs and lose the pedal chain. Fewer parts to fail this way, just push start the bike. If they hit the clutch, you'll get sparks and sadness.
  18. Re-assemble and set the ignition timing to 1.6mm BTDC points, or 1.3 BTDC for CDI. Check operation of all components and tighten cables, fasteners, etc. Check alignment of drive belt at full variation. Use good quality 2 stroke oil mixed at 50:1.