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

 

[SmithDoor]

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

When looking manufacturer the engine back 1970’s. They had square holes for intake and exhaust. For one or two engines a small square file but thousands.

The manufacturers punch the square hole and honed the id.

I was surprised it was a soft steel.

Years late I saw mill that mill the pistol rings it manual hand feed a bank of 3 little mills on a table.

Dave