I have a Zenoah G-26 on the front of my 1/4 scale Sopwith.
It came ready for smoke, with the B&B system, and that's what I installed.

Here's the scenario.
When I run the engine, I get an oily spot in the bottom of the inside of the fuse where the gear is installed. I used to think that I had a leak problem with my smoke oil tank. It's definately not gasoline, I've smelled it repeatedly to verify. It actually has very little smell at all.

Here's what I think is happening. I have a servo that controls the smoke oil valve. That smoke valve is on the firewall, so I use a plastic pushrod to operate the valve. A flying friend was sharp enough to point out to me that he thinks exhaust residue is running from the mounted valve down the pushrod and dripping when it finds the servo. (the servo is indeed covered with the same oil).

What I suspect is that there is backpressure from the engine muffler that is traveling through the smoke oil tap and tubing, and it's getting past the valve and running down the push rod. Then it drips inside the gear compartment.

Assuming this is what's happening, any ideas on how to stop it? It's all the stock setup from B&B, but this is my first smoke system. So any thoughts are appreciated.

check-valve!

Hi Bosch,
Pack the end of the push rod tube with vasoline or bearing grease. You could use a boat style water proof bulkhead coupling.

Dave

I'm going to try the grease.
As for the check valve, do they even make one small enough to fit in line in that small diameter black tubing?

Yep. In both smoke pump instructions I've read, the use of the check valve is a MUST to prevent the muffler pressure from getting its way into the smoke plumbing. You can get one from Don's Hobby Shop.
Sam

You made me go dig out my Zenoa's cardboard box.

In my own defense, I have the instructions in front of me from B&B Specialties, and it does not indicate a check valve in the schematic or the text.

That being said, I agree with the check valve sugestion and I'm going to put one on.

Some valves will leak externally. That oil will collect and follow the plastic pushrod into the fuselage to drip anywhere it can. In the old days we had glow fuel that would follow the plastic pushrods into the fuselage and drip onto the balsa.

The fix was to install a short piece of fuel tubing on the outer plastic of the pushrod to act as a wiper on the inner plastic pushrod. You have to experiment with the length of fuel tubing to obtain the correct amount of wiping versus the drag/load on the servo for throttle action. Very inexpensive and effective.