Part IV: Into the engine

Mechanical Meditations

I can only imagine what my neighbors thought of the persistent metallic tapping coming from my apartment well after the dinner hour last night. When darkness interrupted my efforts to separate the MB5’s case halves, I moved the project indoors. Piece by piece my makeshift shop was reconstructed in the living room. Good thing the girlfriend is away for the week.

The engine had sat in the previous owner’s garage with the side covers off for some time and the clutch, flywheel, and idler gears were caked in grime, so I pulled them all off so they could be cleaned. That’s when I noticed the rough balance shaft bearing.

After tapping on the case joint for what felt like an hour I was able to wiggle the halves apart and gain access to the engine internals. If there's a simpler multi-speed motorcycle engine, I would be very surprised. That balance shaft is the only unexpected component, and I suspect the engineers put it in there to complement the inertia of the crankshaft, not cancel vibrations. A few minutes in the oven persuaded the balance shaft out of the case so that the offending bearing could be removed. It's a common size, so hopefully I'll be able to pick up a replacement locally. I then proceeded to inspect the rest of the gearbox. Out came the caliper and feeler gauges. Everything is well within specs, but the cylinder has some scrapes from a seizure and should be replaced (or as the Haynes authors would say, renewed).

Since it needs to be replaced, I figure I might as well supplant the jug with a larger displacement, more aggressively ported variety. I’ll take a look at Perk LLC and some of the other online moped parts peddlers to see what my options are. 70ccs, here I come!

According to UPS my parts from Huntington Beach Honda and eBay should be here tomorrow. Then I can overhaul the forks and start bolting this thing together! I'm excited to see a motorcycle rise up out of the mass of parts strewn across my living room floor.


Removal treatment for the MB5's gas tank. (800) 787-8326

Haynes Manuals
Invaluable technical information and diagrams.
(800) 242-4637

Huntington Beach Honda
Various OE parts such as gaskets, grommets, and seals.
(714) 842-5533

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