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The 'What did you do in your workshop tonight?' thread

49dimes

Damn I'm hungry
Made some minor adjustments to each individual stand off and locked em down. Spinner to cowl fit pretty decent.

0918171926-00.jpg 0918171924-00.jpg 0918171925-00.jpg 0918171925-01.jpg
 

BalsaDust

Moderator
Thanks. How can you explain why the piston has the tab sticking out of it and the head has a notch for it to go into during the compression stroke.
 

Alky6

150cc
Thanks. How can you explain why the piston has the tab sticking out of it and the head has a notch for it to go into during the compression stroke.
That is a cross flow scavenged engine versus the typical loop scavenged (schnerle) of today's high performance engines. Transfer ports are directly opposite the exhaust. The baffle directs the fuel/air mixture up the cylinder wall around the top and back down and out the exhaust. Without the baffle, the fuel/air would just go straight out the exhaust. Very inneficient and very difficult to make an expansion chamber work on them. The original Mercury outboard engines were based on this design, of course the baffle was a little more of an elegant design in those. These small cylinders don't need much. Lots of cantamination and mixing with fresh fuel/air and exhaust. Also difficult to get enough transfer port area to really make them go. The notch in the head is to make room for the baffle so you can still get enough compression. Highly prone to detonation.
 
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