Engine leaking from tank

Gordinir8 wrote:I just got today two engines i bought from the bay, one is leaking from the tank back plate and i noticed that i must tight quiet a lot the four backplate screws in order to push the probably new ventury o-ring so that the back plate seal with the tank. Is that normal when you are replacing ventury o-ring which is a little thick when new? Don't want to damage something here.

Gordini8: see you already know the answers. But sometimes the backplate screws are actually a little bit too long and do not go in far enough into the crankcase to seat the o-ring properly. Remove the tank and all 4 screws. Slowly screw each screw into the crankcase and measure the amount sticking out of the crankcase. Are they about the same?  Does that make sense?
   If the amount on each screw is about the same, then check the backplate where the screw goes. Sometimes someone screws the screw in too much and damages the screw seat and it leaks. Some people use epoxy to fill the gap, some use the white tape you put around water pipes to seal them, others use different things to fill in the gap between the screw seat and the screw. The key is to not screw in the screw too far.
   The new Venturi gasket is a little thicker than needed. And the key is to screw in each screw a little at a time, then screw in the opposite screw, then go to the screw you haven’t done yet and so on. Then repeat until the screw are tight. Then the Venturi gasket is compressed to fit properly.

Hope that helps.

Happydad  

Just a couple of things. First, where exactly is it leaking on the backplate? From the screws / screw holes, or where the edge / rim of the fuel tank meets the backplate? If it is leaking at the edge / rim of the tank and backplate, the edge may have a small piece of debris somewhere around its circumference. If not, you can carefully wind a piece of dental floss around the ting ridge to act as a gasket. And if it is leaking from the screws, you can pull a few strands of cotton from a q-tip and wrap it around the screw near the head and that will also help seal the screws without any adverse effects. Another thing not mentioned or asked is the backplate metal or plastic? While both will definately warp, plastic easier than the metal ones, the plastic ones are prone to cracking at teh screw holes if overtightened. So just another thing to watch out for.

Metal backplates form cracks in the same area as plastic ones and just as easy. When the engine is assembled, screw the needle valve in just until it seats. Pressurize the tank with a large syringe. With the backplate facing up looking at the screws, place a drop of oil on the screw heads and around the tank to backplate connection. Any leaks will readily bubble. In addition, if you hear leaking out the back screen, it's the o-ring.

The leak was between the metal backplate and tank edge, without the seal inside it seats perfectly but with the seal tank edge can't get into the groove which is clean by the way. I sand the seal down a little and it seats much better now with no serious leaks so I'm gonna order a brand new seal to see how it will go. Also run the engine and sounds ok but I think that I have to reset the piston since it has a 03 mm play (on the ball end side). Still experimenting...

You can just slice off a sliver of medium size fuel tubing as a seal and works very well. Only about the thickness of a credit card is all that is needed.

NEW222 wrote:You can just slice off a sliver of medium size fuel tubing as a seal and works very well. Only about the thickness of a credit card is all that is needed.

One thing to add to NEW222 slicing off a sliver of medium size surgical (fuel) tubing.
I insert a wooden dowel inside the tubing (not a real tight fit but a slip fit) and cut the tubing with the dowel inside (rolling the dowel and tubing at the same time) for a more consistent width of a "O" ring gasket. Make sure your blade is sharp (newer the better).
I make them to a width of no more than 1/32" thick (about .80mm for our metric friends)