2 stroke exhaust port question

[Roger Taylor]

I am in the process of building the Crusader 60 2 stroke aircraft engine and I am working on the cylinder bypass and exhaust ports. On the attached cylinder detail, the exhaust port is shown with a .060" center web making for two .400" L ports side by side. My question is: what is the purpose of the small, circled center divider and is it necessary?

 

[f2cf1g]

To stop the rings expanding into the port and hitting the port edge.

 

[Roger Taylor]

i agree if rings were in the design. The piston is lapped cast iron without rings. Another suggestion was that the the .060" W adjoining web would keep the port from heat distortion in use. OK, but the .o60" width seems too wimpy to do much stabilization of that feature?

 

[josodl1953]

Just omit the web. I have been using model two strokes for almost half a century and I have never seen engines with a ringless piston using such a web. I think you will be better of without it because such a tiny piece of metal in the middle of hot exhaust gases will heat up more than the rest of the cylinder, probably causing distortion.

Jos

 

[f2cf1g]

Agreed.

 

[Roger Taylor]

Just omit the web. I have been using model two strokes for almost half a century and I have never seen engines with a ringless piston using such a web. I think you will be better of without it because such a tiny piece of metal in the middle of hot exhaust gases will heat up more than the rest of the cylinder, probably causing distortion.

Jos

Thanks for that confirmation. I left the web out and hopefully this will be a one run engine after which it will be donated to the Craftsmanship Museum as a tribute to the designer, George Genevro. Dr Genevro was my machine tool mentor, and he recently passed away at the age of 102. I hope it will set in the shadow of the Genevro Titan 60 that was completed by YouTube presenter Mark Presling in 2023