do i need to use a gasket?

mitchg95 Tue Dec 18, 2012 8:34 pm

do i need to use a gasket with this back plate?
http://coxengines.ca/cox-.049-reed-retainer-flanged.html

**RknRusty** Tue Dec 18, 2012 8:56 pm

No, no gasket required.

dckrsn Tue Dec 18, 2012 8:56 pm

mitchg95 wrote:do i need to use a gasket with this back plate?
http://coxengines.ca/cox-.049-reed-retainer-flanged.html

My 2 cents Mitch, If you've dressed the back of the crankcase, you're
good to go. Some use one gasket in front or rear or both. Imho, adding
material in that area increases case volume which is a negative.
Maybe someone can bail me out on this one. Wink

Bob

mitchg95 Tue Dec 18, 2012 9:21 pm

dckrsn wrote:
mitchg95 wrote:do i need to use a gasket with this back plate?
http://coxengines.ca/cox-.049-reed-retainer-flanged.html
My 2 cents Mitch, If you've dressed the back of the crankcase, you're
good to go. Some use one gasket in front or rear or both. Imho, adding
material in that area increases case volume which is a negative.
Maybe someone can bail me out on this one.
Bob

thats what i was thinking, i will probably use only one
thanks, dckrsn

**RknRusty** Tue Dec 18, 2012 9:25 pm

You understand what Bob is saying; adding a gasket increases crankcase volume, thereby reducing performance. They weren't built by Cox with a gasket. That flange is the gasket.

mitchg95 Tue Dec 18, 2012 9:29 pm

i understand now, i was thinking that i should use one because this shows one is included
http://coxengines.ca/cox-.049-engine-overhaul-kit-die-cast.html

mitchg95 Tue Dec 18, 2012 9:42 pm

RknRusty wrote:You understand what Bob is saying; adding a gasket increases crankcase volume, thereby reducing performance. They weren't built by Cox with a gasket. That flange is the gasket.

decreasing crankcase volume allows for greater crankcase compression thereby giving more power

**Admin** Tue Dec 18, 2012 10:18 pm

My 1990 Black Widow that has that slip on reed retainer came with a gasket and so does all my Killer Bees. All the gaskets are placed over the flange so the gasket comes in contact with the metal crankcase. Even though the gasket will add a little more volume to the case, it is better than an air leak. Unless you lightly sanded the back of the case perfectly flat and it doesn't leak without a gasket, I would use one.

**RknRusty** Tue Dec 18, 2012 11:09 pm

Once again, Cox mixes things up. I have bought 5 pre-1996 NIB BWs(3 of which were bought back then at hobby shops) and none had a gasket between the flange and either mating surface. I don't use gaskets in them. Either way works fine.

mitchg95 Tue Dec 18, 2012 11:24 pm

RknRusty wrote:Once again, Cox mixes things up. I have bought 5 pre-1996 NIB BWs(3 of which were bought back then at hobby shops) and none had a gasket between the flange and either mating surface. I don't use gaskets in them. Either way works fine.

once i get my tach ill get the engine all together without the gaskets

Cox International Wed Dec 19, 2012 10:12 am

Technically, one does not need a gasket for the black and red, flanged, reed retainers.

Estes/Cox sometimes used a gasket and sometimes not on the black version. On the red version (Die Cast engines) they seemed to always use a gasket.

Again, you don't need one but we use them on all our engines and rebuild kits to avoid the inevitable "the gasket was missing" email confused

mitchg95 Wed Dec 19, 2012 1:47 pm

Cox International wrote:Technically, one does not need a gasket for the black and red, flanged, reed retainers.

Estes/Cox sometimes used a gasket and sometimes not on the black version. On the red version (Die Cast engines) they seemed to always use a gasket.

Again, you don't need one but we use them on all our engines and rebuild kits to avoid the inevitable "the gasket was missing" email

thanks for all the information guys, I put my engine back together without the gasket. I will test run when i find some time and $ to go the my lhs and get a tach, and 30-40% nitro
Mitch

Paulgibeault Wed Dec 19, 2012 11:33 pm

In my discussion with Cox Venom engine designer Larry Renger. Larry stated the factory specification was that there be one paper gasket placed on top of the nylon reed retainer.
If the gasket is missing (or even deteriorated), I have found that it results in a leaky tank.
Engines with leaky tanks still run, but certainly don't run as well or as steadily as they should...

I tend to think the paper gasket affecting "crankcase packing" & primary crankcase volume, etc. is a ruse.... Until proven otherwise, I wouldn't recommend omitting the gasket.

Merry Christmas Everybody!

Cheers, Paul

**RknRusty** Thu Dec 20, 2012 8:47 am

And there we have it.
For those new around here, Paul is an accomplished mouse(Cox tanked Bee) racer and internationally known speed flier, and is well known in competitive racing. I would consider him to be the argument buster in this case. I'll be adding a gasket from now on.

Here's his article about getting the most out of your Bee.:
https://www.coxengineforum.com/t753-the-revised-2011-gibeault-mouse-race-program

**Cribbs74** Thu Dec 20, 2012 9:59 am

Not that I can add much to what Paul said, but from personal experience with a leaky black widow, even with a lapped case I was still leaking air around the screw holes until I added the gasket. I would pressurize the tank as it will let you know where all the leaks are.

Ron

mitchg95 Thu Dec 20, 2012 10:39 am

well i dont need any air leaks, ill put the gasket back

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