Tuesday, April 17, 2012

Stuff I Do for Fun............. Update

Rebuilding a Honda 50 (C100) from 1960....

The Honda C100 we are restoring has a piston that measures 39.98 mm in dia. or (1.57 inch).

My research tells me the standard cylinder bore is 38.125 mm (1.50 inch) ... meaning the engine we are trying to restore is already overbored.
Assuming the wear on the piston skirt and cylinder wall from scuffing...
And beginning with a normal piston to cylinder clearance of 0.020 to 0.030 inch we have a cylinder dimension of close to 1.575 inch.

The max overbore size for standard pistons is 0.075 inches?

Maybe we can fudge it with easy-does-it honing and piston clean up.

Maybe we will have to go overboard with a custom piston...?

Of course .... once you start going there ... why stop?

Are oversized valves next? Are we going to be hot-rodding the engine?

Cylinder (note the scuffs on front and back wall areas)

Top View of Rocker Cover (Rusty)

Inside of Rocker Housing (Not bad but note casting rusted)

Top View of Cylinder Head (Casting Rusted)

Bottom View of Cylinder Head ( Exhaust valve carbonized)

Exposed Piston (Piston top is burnt severely)
Now ... in spite of all that carbon and rust this engine was running when it was put in the barn!

The plan now is to disassemble the cylinder head and clean it up. Need to machine out the exhaust seat and install a hardened seat for using unleaded gas, replace the exhaust valve and recondition the rest of the parts.
The cylinder will get a rebore and once that is done we will choose a new piston and ring set. My guess is that 0.010 - 0.020 " over will make the jug round again.

The carb will get replaced .. the old carb is rebuildable but I can sell it after the project is done.

No plans to split the cases at this point. Replace the ignition parts for strong spark and rebuild the centrifugal clutch for good grab.

The rest of the scooter is getting painted and refurbished right now ... so as soon as the mail order parts come in we will have everything needed to put this little piece of history back on the road.

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