I made a 2nd ring muffler for my ASP radial engine. This time I incorporated a tube in the exhaust outlet to attach the oil drain line too. The tube is extended downward in the outlet, so a low pressure is created and helps suck out the drainage.





I thought this was a great idea.

I'm not so sure though. Because the engine ran a lot differently this time.

First, I had messed with the carb needles. That was a mistake because the engine ran lousy until I reset the needles back to where they had been on the last two runs. Once I did that, the engine started immediately, had great transition from idle to full power like before. But the peak RPM was down, by about 1100-1200 RPM!

I was thinking at first that maybe the new exhaust ring was more restrictive than the first version and that was the cause of the RPM loss. But the HS needle was much more sensitive this time compared to last. Why would that be? The collector ring? I was not sure. As I ran the 2nd tank of fuel through the engine, I noticed something else really strange. Blow-by oil was bubbling out from the base of the #1 cylinder pushrod tubes. This has never happened before.

So I was wondering if my drain line through the exhaust outlet was not flowing as well as before. Even though, I could literally see the stuff being sucked rapidly through the silicone line into the exhaust outlet. However, when the tank ran dry and the engine shut down, there was a lot of discharge for a few seconds flowing out the drain tube from the exhaust pipe.

If the crankcase was getting filled up a bit, I could see that as the reason for the loss of RPM. Oil attaching itself to the crankshaft and weighing it down.

By why would the drain line from the crankcase now being helped by the suction of the exhaust, instead start to fill up the crankcase?

The OS radial engine has the same drain nipple. Have any OS radial engine users experimented with this drain line, or observed any unusual reactions to a partial restriction or anything?