I just finished cleaning and RTV'ing a couple of old engines (Airplane ProMagnum ABC .45 and OS .21 VF-BR buggy). I RTV'd crankshaft, back plate, carb base, and exhaust/muffler. I used no paper gaskets. Instead I used Permatex Ultra Copper High Temp as suggested in this forum.

To test the quality of the seals, I plugged the exhaust port and the carb, closed the needle valve completely, and use a fuel hose attached to the muffler pressure fitting to blow air into the engine.

My muffler is completely sealed as there is no leakage when the piston is covering the exhaust port.

Lowering the piston allows air to flow into the crankcase and out of the open carb. When I close the carb with my thumb there is still a small amount of air leaking. It sounds like it comes from the throttle barrel (carb was also RTV'ed). Is it normal for the throttle barrel to leak? Or should I have NO air leakage? Maybe its the mixing valve?

How can I test to make sure that the RTV seals are properly sealing?

Thanks.

Albert

Albert:
Shouldn't leak much unless it's an airbleed carb. Dunk it in some varsol or kerosene and you'll be able to see exactly where it's coming from. I use the same method only from the other end and using a large fuel line over the carb intake and turning the crank till the exhaust and transfer ports are closed.

The throttle barrel will usually have a slight leak. It has to be a loose enough fit to turn easily with a servo and there are no seals except the close fit. The final proof is in the running. If it will develop normal power and idle down to a consistant, steady idle, you don't have a significant leak. Of course if the barrel is leaking a lot of air, it may have to be replaced as it's probably scored or badly worn.