Fuel tank/Crankcase Gasket

Canso07 Mon Dec 12, 2016 8:29 pm

Hello Everyone,

Just joined the forum, I've always been into C/L flying and love the Cox 049. Got one question here, if your using the plastic reed retainer should you put a gasket on either side of the retainer? or does the plastic retainer act as a gasket? I just bought the the Xena's Pink Panther and noticed they had a gasket on either side of the retainer. But if look on older instruction/part list's they just show the plastic retainer being there. Any help much appreciated.

Curtis.

NEW222 Mon Dec 12, 2016 9:45 pm

My Estes Black Widow engine has only a gasket at the rear, behind the plastic retainer. I bought it new so that is what was installed at factory. But, if Cox International installed one fore and aft, I would just leave them and have at it. Just my .02.

P.S. Welcome to the forum.

Canso07 Mon Dec 12, 2016 10:01 pm

Thx NEW222. Interesting your black widow only has 1 behind the retainer... yes I'm going to leave the pink panther alone but in my past/future builds gaskets or no gaskets...lol

Thx again Curtis.

roddie Tue Dec 13, 2016 12:18 pm

Hi Curtis, Others have asked this question, including me. I can't seem to get a definite answer. I feel that a gasket should be installed forward of a cap-style reed-retainer. The back of the crankcase where the sealing needs to happen, can be a slightly uneven.. or rough. There may be a ridge of "flash" from machining or a burr somewhere that's hard to see. A fibrous gasket should seal these areas. Mating the cap-style reed-retainers' flange directly against the case might not. Some modelers "smooth" the back of the crankcase by gently rubbing it over super-fine (600 grit) sandpaper placed on a flat (preferably glass) surface. This knocks-down/removes any irregularities. Just a few orbital-strokes at a time.. while inspecting in between.

It's a good habit to inspect this area closely when assembling an engine. There could be old gasket-remnants from a previously-run engine, that need to be removed. When assembling the tank/back-plate, make sure that "all" the screws tighten before they "bottom" in the case. Some screws may be slightly long.. and/or the threads in the case could have been tapped slightly shallow. If the latter; the case-threads can usually be re-tapped deeper with a 2-56 tap. If the screws don't tighten, the back-end won't seal.

On a tanked-engine, be sure to re-install/replace the venturi-gasket. Think of a tanked-engines' back-end (rearward of the case) as a pump-housing. Any air-leaks here, will reduce the pump-action when the reed opens.

balogh Tue Dec 13, 2016 12:30 pm

In my opinion the gasket should come between the retainer and the cranckase, especially because if you place it between the backplate and the retainer, the free play/travel of the reed will increase by the thickness of the gasket, and this will reduce the time of closure by the reed. In the worst case the charge sucked into the cranckase may partly be lost when the piston moves down, the cranckase is supposed to be pressurized, but instead, the charge escapes through the venturi with the reed still not closing the venturi...

Once I put the gasket the wrong way i.e. between the retainer and the backplate and could hardly start the engine up, only to see a very erratic run.