Model Forum / Radio Controlled / Air Models / January 2007

Cox fuel was 25% Castor, 25% Nitromethane and 50% Methanol.
Refer to other blends under :Fuel facts & FAQ + Fuel Tank installations: on
my webpage and also refer to the main COX enthusiasts web page and download
manuals
Cox engine - "How to Get Best Performance" Cox manual. .pdf
Cox engines
http://www.mh-aerotools.de/airfoils/cox_start.htm
or email me for some other Cox manuals not listed on that site.

Regards
Alan T.
Alan's Hobby  Model & RC Web Links
http://homepages.ihug.co.nz/~atong

Be really careful with RC car fuel.  Cox engines were designed to run
on fuel with castor oil.   Too many RC fuels today have low oil content
and most of that synthetic.   Cox engines use a ball and socket joint
where the piston and connecting rod come together and just a few runs
of synthetic oil fuels can ruin one.   Sig sells castor based fuel and
the 1/2A fuel sold by Tower has enough castor to work (but maybe not
enough to keep your engine for years).   Remember that Cox engines are
out of production so parts are an issue.   You might look at current
production engines like the Brodak Mk I or Mk II.   The Mk I made by CS
and is a sport motor.   The Mk II is made in Moldavia (sp?) and is a
high performance motor.   For what you can get selling a Cox engine on
ebay you are well on your way to paying for a $49 Mk I or a $59 Mk II.
Do a google search on Brodak they are one of the biggest suppliers of
Control Line items in the US.
Bob Furr

I used to run .049s and .051s on 40% nitromethane, 20% oil fuel, and the
oil was 2/3 Klotz, 1/3 castor.  The engines had their own peculiar ways-
 the cylinder and pistons never wore out as long as you reset the
ball-in-socket joint occasionally,  the older production cranks had a
too-thin web, and these would eventually break at high rpm.  This was
corrected around 1972 or so when Dale Kirn pointed out the weakness to
Cox.  Later cranks are heavier in the web.      -Paul

You have the nitro percentages correct - 15% for the regular fuel, 30% for
the racing fuel, and as far as I know the oil was 22% castor.

15% nitro is fine for .049's but you should consider it a minimum level for
decent running habits (not for smaller though - 25% for .010's and .020's) .
10% "runs" in Cox .049's according to some people, but in my honest opinion
it totally sucks and I've run a lot of these engines in my lifetime so far.
They love 25-30% and burn that with about the same level of stress as a .40
on 10% so don't let the relatively high percentage sway your opinion. The
oil content should be minimum 20% and a good percentage of that castor. If
you cannot find a can of "1/2A fuel", Sig Champion 15% - 25% in the 20% oil
variety is a very good choice. As bare minimum, and I say this with
reservation, use 18% oil minimum, but this should be at least 50% castor.
Many LHS's carry bottles of SIG castor oil, so if you can't fnd something
decent off the shelf, buy some 15% or better yet 25% nitro fuel with 18% oil
that uses a syn/cas blend, then add about 4 ounces of the castor to a gallon
jug. Or proportionally less for smaller jugs.

Avoid car fuels like the plague. They often run ridiculously low oil
percentages and high to all synthetic. You'll beat the crap out of that poor
TD .049 with those fuels. The advice regarding the ball and socket small end
joint and it's need for mucho lubrications is good advice.

MJD

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