TWN Contessa - Engine

page updated February 19, 2011 by Dave

The diagram below illustrates gas flow around the engine. It should be noted that although the Cornet motorcycle and Contessa Scooter share some engine parts, such as connecting rod and pistons, most other parts are unique to each. On the Contessa, the carburettor and exhaust are on the left cyclinder with the transfer ports and spark plug on the right cylinder. The Cornet motorcycle is the opposite way around (i.e. different head and barrel).

 

Contessa crankshaft, barrel and pistons.

 

Bing 26mm carburettor.

 

Detail of clutch assembly.

 

Complete engine in frame.

 

Detail of air flow through carburettor.

 

Idea for float needle modification, but problem solved after new cork washer fitted to petrol tap. Modern Vespa butyl ones will fit in tap too.

 

This shows a rough drawing which was sent to Motorrad-Stemler.de who sells Cornet motorcycle pistons. He had no idea if they were suitable for the Contessa Scooter. It turns out they 'are' suitable, apart from having only 2 rings per piston as opposed to the originals which have 3. The drawing also highlights that the pistons have dissimilar gudgeon pins, one having a closed end (geschlossen). (Note different item numbers 14 and 15 on Schematic 1). This gudgeon pin must be fitted to the left piston with the closed end to the left also, where it will blank off the exhaust port.

 

 

Some rough notes taken from parts sheets photocopies. Choke cable on my scooter was a broken tangled mess.

 

Various bearings and screw sizes highlighted.

 

Teach yourself German.

 

Plugs old and new.

 

Exhaust system.

 

Spark plug equivalents.

 

How many corks in a Contessa clutch? 60 please.

 

Two oil seals fitted to rear wheel sprocket.

 

Fan cover and cylinder cowl - before scrubbing by hand with Alloy cleaner then sprayed with silver paint.

 

Spare exhaust.

 

Spare engine which provided a crankshaft for original engine.

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