New Aluminum Backplates

If al fail try wit the permatex moto seal. Grey for cases gasket It may work bether than just a seal the fuel tube trick is also Not bad idea i have instal 3 of those on m'y customised engine one of them.is used with a remote line So it will make little difference if it leaked but I did not have this problem I used new round seals That I had on hand from? Lighter and something else I must have put together a bunch of small seal in a small container it was not oem cox parts

GallopingGhostler wrote:............so I took a thin slice of silicon fuel tubing and used that. It worked like a charm. If yours needs a thicker one, my methodology should work.

George's technique works a treat.

Sometimes, I've had difficulty cutting a clean, straight edge and uniform thickness, particularly when the tubing flattens out, even when using a sharp razor blade. For me, slipping the tubing over a bamboo skewer, then rolling it while cutting gave a better result.

I also purchased a couple of packs of different sized soft Buna-N O-rings from McMaster-Carr that worked well, but I can't provide sizes at this time because I can't find them right now.

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Trick to my technique is a new Exacto or razor blade, it must have like new sharpness. The good thing is that you can practice until you get the right cut that works. Fuel line is inexpensive.

$2.40 for 25

https://www.ebay.com/itm/140731004114?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=140731004114&targetid=1262779893729&device=c&mktype=&googleloc=9021893&poi=&campaignid=14859008593&mkgroupid=130497710760&rlsatarget=pla-1262779893729&abcId=9300678&merchantid=6526584&gclid=Cj0KCQjwmdGYBhDRARIsABmSEePfZOyzy2VRVrSV9GM2cXvv9daPcoDcBCngCc_WqnJ-ryolJHautmYaAlegEALw_wcB

Mark -
I have tried the dart tip gaskets before and found, while they usually worked, I could get a better fit by selecting specific sizes through McMaster-Carr.

If I recall (a task growing more difficult over time), the thickness of the O-ring would sometimes keep it from seating completely on the venturi stem. OTOH, it may have been that the dart set I purchased were slightly larger than normal.

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We had 1,000 of the alu backplates manufactured (1/2 stunt / 1/2 non-stunt / 1/2 silver / 1/2 black) and shared the production run with Ex Model Engines; whereas a different vendor supplied the spraybars; which we pressed in.

Unfortunately, some of the spraybars were outside of specs; something we did not realize until we had already shipped a few backplates. Once we became aware of the issue, we re-tapped the spraybars and tested the backplates individually for good seal for when the needle valve is fully inserted.

A good way to do this is to attach a short piece of fuel tubing to the fuel nipple, turn out the needle valve about four turns and suck on the tubing. Then, turn in the needle valve completely and keep sucking. If, when the needle valve is completely turned in, air still flows freely when sucking, then the spraybar is defective.

Of course, anyone that purchased a defective product from us, should contact us so that we can make them whole.

andrew wrote:Mark -
I have tried the dart tip gaskets before and found, while they usually worked, I could get a better fit by selecting specific sizes through McMaster-Carr.  

If I recall (a task growing more difficult over time), the thickness of the O-ring would sometimes keep it from seating completely on the venturi stem.  OTOH, it may have been that the dart set I purchased were slightly larger than normal.

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I had the same problem with dart gaskets, the were too thick. Started cutting fuel tube and they work good even if not cut perfect.

crankbndr wrote:

andrew wrote:Mark -
I have tried the dart tip gaskets before and found, while they usually worked, I could get a better fit by selecting specific sizes through McMaster-Carr.  

If I recall (a task growing more difficult over time), the thickness of the O-ring would sometimes keep it from seating completely on the venturi stem.  OTOH, it may have been that the dart set I purchased were slightly larger than normal.

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I had the same problem with dart gaskets, the were too thick. Started cutting fuel tube and they work good even if not cut perfect.

George's silicone right?

https://coxengines.ca/fuel-tanks-lines/vinyl-fuel-line-for-cox-engine-010-020-clear.html
https://coxengines.ca/fuel-tanks-lines/silicone-fuel-line-for-cox-engine-049-051.html

Yes silicone and you only need a sliver!! LOL

I used silicon, blue tubing for half-A, don't remember where I got a bulk length, may be Hobby People (formerly Hobby Shack) when visiting the area a while back (just before they closed forever). It has a thicker wall than vinyl, plus has more give, "springiness". My general feelings are that vinyl is more rigid and probably doesn't have sufficient give, unless you cut a slice that is "just right". Silicone has more forgiveness, you don't have to quite as precise with it.

crankbndr wrote:Yes silicone and you only need a sliver!! LOL

That is just what I did, and it worked. When out of stuff and to get an engine working, I found a way. It was my son's .049 Babe Bee that I rehabilitated a while back.

It all started with the skills I learned while with Sanchez Academy of Karate in Gallup NM back in the 1990's, was with them for 5 years. It honed my ninja hands to be able to chop a very thin slice of silicon tubing (blue - I know, very old stuff - but silicon doesn't seem to age like surgical tubing.) Thus I was able to put the engine back into the sparring ring. May be in a future match, it will win Cox Engine of the Month and get its next belt.

Some of the lightning have left my hands, but chopping silicon fuel line, still got the knack.

I never found the blue tubing to be worth a hoot. The only blue tubing I ever found worth the space it took up was the Aerotrend fuel tubing. The Dubro crap is worthless. It not only fits improperly usually falling off of the barb, it swells with age. Not that I'm suggesting what some are doing is incorrect because I've done so myself. What I've seen is that unlike a true o-ring, the tubing has square edges which tends to splay out when in compression or overcompressed.

          Whenever I've cut fuel tubing to seal needle valves for instance, I slide a piece onto a bb-q skewer or similar dowel. I use a piece about 2" long, slide the tubing onto it, chuck it into the drill press and using medium speed and a new single edge razor blade, I hold it as square as I can to the tubing. You can cut multiple thickness pieces and you can easily see what pieces aren't accurately square. The pieces slide right off of the dowel and you can discard what is inaccurate.

      The simplest way to insure the venturi isn't leaking is to screw the needle valve all the way down and completely bottom it in it's seat. Obviously, don't overtighten. Pressurize the tank using a syringe and inflate it like your trying to pop it. This is going to require a finger or vent cap on the opposing nipple. You can hold the engine screen up and place a drop of oil over the hole or screen. The surface tension of the oil will keep it in place over a open venturi or screened version. The oil will bubble or you will audibly hear air escaping. Not only will it determine if you have a leak in the venturi, it will also determine screw leaks, leaks at the tank to tank back, crankcase to tank and also needle valve seat or needle itself. All of these area can easily be detected by listening or oil.

Ken Cook wrote:I never found the blue tubing to be worth a hoot. The only blue tubing I ever found worth the space it took up was the Aerotrend fuel tubing. The Dubro crap is worthless. It not only fits improperly usually falling off of the barb, it swells with age. Not that I'm suggesting what some are doing is incorrect because I've done so myself. What I've seen is that unlike a true o-ring, the tubing has square edges which tends to splay out when in compression or overcompressed.

Ken, I have no idea who the maker nor distributor for this tubing is. It is smaller than standard line I use for the .049's, probably best suited for the barb on 1/4-A's, is a real bugger to place on a horseshoe back engine. (Since I have not put to use any of my horseshoe back engines, so far it i not a problem.) I am down to a 10" piece now.



So, size was not an issue. The original Cox tank venturi gasket was flat, so, I mimicked that. Regarding squish, squeeze, bulge, etc., I have no idea as once I installed it, I left it. It worked. "If it works, don't fix it."

It is a very pale blue, I have larger size and where this stuff doesn't fit, I use the other.

About the only other thing I would like to now get is my hands on some silicon wire insulation, to replace the fuel line on my R/C Bee. May be they sell the stuff more readily in Europe, because I have yet to find it in the local home improvement centers.

GallopingGhostler wrote:

About the only other thing I would like to now get is my hands on some silicon wire insulation, to replace the fuel line on my R/C Bee. May be they sell the stuff more readily in Europe, because I have yet to find it in the local home improvement centers.

George -
An eBay search on: 14 gauge silicone wire will get you lots of hits.  I've found eBay to be a fairly good source for bulk electronic components with decent pricing and reasonable shipping.

14 AWG insulation works well for me, but larger or smaller wire gauges are also readily available.

Also, a search in the BNTECHGO Store on Amazon should provide a wide selection of choices.  I've used the BNTECHGO brand of wire, smaller gauges, when doing HO locomotive repair and restores and found it quite acceptable.



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