Engine Documentation

 Contact Points

 Clutch

 Oil pump drive gear

 Flyweel rotor

 Final drive

Boring and honing cylinders.

I had the cylinders bored and honed at a local machine shop .25mm over, which is the first oversize, to receive NOS pistons I picked up on Ebay.


Top End

• Sandblast and powder coat cylinders and heads, matte black.
• Overbore the cylinder .25mm
• NOS 54.25mm pistons
• NOS Piston rings
• Refurbished and Zinc coated head bolts
• Yamaha head bolt washers
• Yamaha Exhaust gaskets
• Copper head gaskets
• Yamaha cylinder base gaskets
• NGK B8HS spark plugs

Before and After

Cylinders and Heads

247~250cc Displacement

Make sure all threaded holes that are meant for screws/bolts are plugged prior to powder coating.

 BEFORE

AFTER, Sandblasting and powder coating.

Start rebuilding

Freshly powder coated motorcycle frame.

Getting into the engine...

 Top end removed and contact points side cover.

One piston, cylinders and heads removed from the top end of the engine.

Documentation

I try to do as much documentation as possible to help aid reassembly, (i.e. photographs, diagrams, laying things in order, zip-lock bags) organization is key.

Engine

Here are a couple shots of the engine once I pulled it from the frame of the bike.

Tear Down

Not the best picture ever but, I just started stripping things off and eventually got to the engine. Make sure to keep all bolts and washers, small parts, sealed in zip-lock bags so reassembly is a breeze. This older Japanese bike came fitted with a lot of Phillips fasteners that strip extremely easily even with the most caution. I recommend investing in a screw extractor set.

DS7 Update-Two Stroke Cycle

Basic specifications of the bike:

Year:1972
Make:Yamaha
Model: DS7 
Engine Displacement: 250 Cubic Centimeters
Two Stroke, This means that the piston and connecting rod take two strokes to one crank revolution, one down and one up, to complete a full combustion cycle.

This is the basic two-stroke combustion cycle