Cougar429

My Feedback: (3)

The purpose of the vent is to allow contaminants and used lubricant that make it past the ring to escape, as well as allowing the case to equalize as the piston moves up and down, (varying the internal volume). You want that to be as short and/or as large a diameter as possible to prevent negative pressure from drawing them back in. By tying that into the muffler vent line you are pressurizing the case with the same source as what aids in fuel feed to the carb. This would prevent good scavenge. If you use fuel running out the muffler to indicate when the tank is topped up during fueling a good slug of fuel can then make it back into the case.

As the engine is running the vent is pretty active and physical aeration by the crank and piston movement can mix those contaminants with the lube oil to be carried out the vent. If this is restricted in any way more of that will remain within the case. From what I've seen it starts to do its nasty work once the engine is idle. Some of those contaminants, such as residual unburnt fuel, combine with water vapor, (also a byproduct of combustion as well as what is drawn back in the vent as the engine cools and changes with environment) to create corrosive chemicals that go after anything ferrous inside the engine. The victims are the crank and cam, piston pin and valve train. Especially vulnerable are the bearings, as any damage to their surfaces can quickly start further failure, along with the particles now able to inflict damage to other components. Better quality bearings are more resistant, with stainless being the least vulnerable next to ceramic, but any metal bearing can be attacked by these corrosives.

I would say that if you want to keep vent outflow from adhering to the fuselage, install a good diameter line long enough to do the job. I've included a couple of pics that best illustrate what I've described. To get the vent clear of the large cowl on Rare Bear, the Saito 125 has a short piece of soft silicone tube fit to the back of the case and a larger diameter plastic line. This has roughly twice the ID of typical fuel line, but the silicone tube is pliable enough to expand to fit.

ps. I have been using plastic tube for all my fuel/vent runs for years. By slowly heating the tube you can bend it to whatever you need with little alteration of diameter, (takes a bit of practice). Unlike brass, this also remains flexible enough to allow for removal of the tank or other components. In many cases the third line is the fill/defuel line formed to follow the inside of the tank to the lower left corner. This does not interfere with the clunk operation at all and allows for complete emptying when done for the day.