FOX 35 ABC (Aldrich MOD) question

I have just purchased a Fox 35 that was made ABC by George Aldrich. This is an almost new engine with only a few tanks run through it. It seems to start very hard (I can only get it to run with an electric starter). Is this a function of break in? How much time does it normally take to break an engine like this in? And last of all, what prop would be a good choice for this engine? I am using SIG 10% 25% all castor fuel. Thanks for the help, Dave Markley

Dave, I have one also, and mine starts and runs well. I hand start it in usually one or two flips. Does yours have good compression? If it does, and you flip it through compression, does it have a deep "chug" sound as they do when they have good crank case compression? I would be happy to check it out for you at no charge, but you would be expected to pay shipping both ways. I have heard that Fox mfg has discontinued the manufacture of their ABC setups, so there will be no replacement ABC sleeves from them if the sleeve is gone. Check the backplate gasket for breaks. If it has a stuffer backplate on it, there is a good liklihood that it is broken and leaking. If it is, that is possibily your problem.
Bigiron

Well, someone asks this question about once per week, so I'll suggest that you check the archives.

BUT: Break in on a 9" prop untill your engine is broken in. Then chenge to a castor synth blend. An ABC engine should tolerate that mix ok. Standard Fox mix is 29% Castor. Remember that!

ALSO: LOOSE THE STARTER! You can ruin your non BB engine real quick if the starter forces the crank back against the backplate.

Just take your time and do it the hard way. You'll benefit in the end.

BIGS

" What constitutes the dignity of a craft is that it creates a fellowship, that it binds men together and fashions for them a common language. For there is but one problem - the problem of human relations."

There's a fairly good chance that this is a Russian-made, Imported by Danny Dirt, piston/cylinder. SOP with new ABC is to "back-slap" the prop to get it to fire off without having to knock it over TDC with the flipper finger (an owie is almost ensured). No, I've never had any luck with it, either. Steve

>SOP with new ABC is to "back-slap" the prop to get it to fire off >without having to knock it over TDC with the flipper finger (an owie is
>almost ensured).

Might be true of all ABC/ABN motors. I've got an RC Thunder Tiger .46 Pro (BB w/ABN) in which I've gotten pretty good at spinner starts. Just grab the front of the spinner and give it a quick clockwise twist against the compression stroke and it's off and runnin'.

I have a Fox ABC, Russian P and C, GMA engine, also. Smoother than its stock cousin, but no added power, I think.

Have it on a Sig Fokker profile. Currell

Another thing-- Check for head gasket leaks and glow plug leaks. You should be able to start the engine by hand easily.

Bigiron

Here is George Aldrich's definitive treatise on how to breakin ABC engines and what fuel to use.

ABC//AAC Engines—What They Are, How To Run, and Treat Them by George Aldrich:

1. The basics of how these systems work.
a. The piston material, a high silicon aluminum alloy, has a far lower coefficient of expansion than the cylinder material whether it is brass or aluminum.
b. The cylinder material is either high tensile brass or aluminum that is chrome plated.
c. The combination of the highly abrasion resistant piston material running in the very hard-chromed cylinder assures long life.
2. Why does the piston have such a tight fit (pinch) when the engine is turned over TDC (Top Dead Center)?
a. The high tensile brass or aluminum cylinder expands a great deal more that the piston when the engine reaches operating temperatures.
b. If an engine is set up with what most consider the normal fit and the usual bore that has little taper, then when the engine reached operating temperature, it would have little compression! With a straight bore, when an engine gets hot, it suffers from what is normally called “bell mouth”! The symptoms of bell mouth are great cold starting, but poor hot restarts.
c. When I first started working with the first ABC engine ever sent in the U.S., (1966) the first thing I did was to lap the piston to the fit we had developed with cast iron/steel assemblies. This basically ruined it! Form this early beginning, it was found that a tapered bore fit much tighter, was required to get this system to work at its best.
d. Later technical advancements in being able to hard chrome aluminum, led to using aluminum cylinders, and the high silicon aluminum piston, for what we now call an AAC assembly today.
3. We now have an engine that often squawks, and makes other “funny” noises, when it is turned over. What is the best way to run these engines? Because of the tight fit, it’s not hard to see that the moving parts that carry the loads will have extra stresses put on them until the engine reaches it’s maximum running temperatures. Because of this, the most critical time is the First Two Minutes that are put on the engine. Therefore:
a. The first run on this type of engine should bring it to its maximum RPM’s, just as soon as possible, or Wide Open! The idea is to get the engine to its maximum temperature quickly to relieve the extra loads imposed by the tight pinch!
b. After the first two minutes of running, you can set the engine however you choose, and just Go Fly!
c. You will see such an engine just get better and better with more running.
4. With an engine that is a true ABC/AAC type, I have found that a fuel containing a total of 22% lube mixed 11%/11% castor/ synthetic is ideal. This particularly true, when using a muffler, or piped set up. The castor carries the heavy loads, and the synthetic acts as a detergent, reducing the varnishing that occurs with all castor fuels. I have never subscribed to the special “hemi-head” and “stuffer” back plate offered for the Fox .35. While working for Fox, I ran tests with Duke on an engine that had a piston and cylinder mounted in the back plate. Duke would start the engine and I would vary the crank case volume by pushing the piston in and out while Duke recorded the results. Duke knew Exactly where his engine ran the best! This engine now resides on the top shelf of the Fox display in our AMA Museum in Muncie.

GMA