Tee Dee .020 Tank seal?

Thanks, Jason, for the fast reply!

I guess I'm lining up a tank back cover, or I'll get another one of those aluminum backplates from Gary over at RCG.

Off topic...anyone find a need to use crankcase pressure for fuel delivery on the .020 Tee Dees? I'm considering the aluminum venturi blocks for a pair of these little jewels. Unlike the plastic ones, there is no nipple to break off.

It's more of a post for the starter spring was never really formed to function as
a good grabbing nipple for pressure line. If the starter spring is used the post can't
be accessed to use as a parking spot for a pressure line. It was later seen as an
advantage to tap for pressure. I have thought about tapping the aluminum carb
body for a pressure nipple as shown. The advantage is a post for the spring as well
these size nipples are very small as they should be for a TD .020. The loop made
in for the spring to catch the post will have to be opened up a hair bit to go over
the hex section of the nipple. I use springs on my aluminum carb bodies for the
TD .010 it is a absolute requirement for such a small displacement. I do use
my Hornet 1/2A starter on the TD .020 but would not mind using a spring the
down fall is they mar the carb body and collar. If used the pressure tap would
allow the chance to bore out the venturi a bit to take advantage of the additional
fuel push for some more top end rpm.

Ole' 1/2A Nut is a well-known go fast guy and knows his stuff. For general sport flyers like myself, the TD .020 has adequate fuel draw with a vented tank. The plastic tank backs are indeed brittle and easily cracked. Tinked a few myself from overtightening. I've found the new MECOA parts to be more sturdy than the old OEM ones I've used. The backplate mount/external tank is also a good option, especially of you desire a longer runtime. The engines were shipped originally with a plastic backplate mount in the box and they can still be purchased from MECOA as well. A better option is the pretty little machined aluminum backplates available from a seller over at RC Groups 1/2A forum. I recently got some in the .010 and .020 sizes and am impressed.

https://www.rcgroups.com/forums/showthread.php?3039268-Cox-Tee-Dee-010-and-020-Aluminum-Backplates

The above link will get you to the backplate mounts they are top notch aftermarket add on's that will
improve your engines performance.

Funny that this topic should come up tonight as this is something I'm tinkering with.

Need to put oil around the O ring area before snapping it into place I oil the hex bolt threads too.

I picked up two already!

The seller told me to watch out for the cylinder
dropping low enough in the block to foul the aluminum backplate. Sure enough, on one of mine the cylinder stopped the installation.

I pulled the oring and lightly kissed the top of the part that goes into the block with some 240 grit and 400 grit. I doubt I took off more than .002" to get the cylinder cleared.

How much fuel does the OEM tank hold?

When you get down to it the millionths of an inch precision was just on the piston/cylinder fit. Take a caliper to a bunch of engines of the same type and you will see enough variability to see tolerance stack up to cause issues like the cylinder protruding into the crankcase.

I believe I discovered the issue with the .020 backplate interference. One engine was fine and the other I couldn’t install the backplate in. I started measuring other TD .020 engines and found differences in each engine in the length of threads on the piston and the height of the crankcase top lip where the piston seats to. I don’t think the slight divot it puts in the backplate is going to hurt anything as the o-ring still seals it up.