Fox .35 ID, and Needle Assembly Question

[Chancey Chorney]

Hi there.  I have a couple of questions pertaining to a Fox .35 engine I have.  I had acquired this engine approximately 15 - 16 years ago.  It was well used and in ok condition.  But I took it apart and had crock potted it back then shortly after acquiring it.  I bought and installed a rebuild kit for the engine, as well as a needle valve assembly.  I have also not yet run the engine, but the questions are regarding the rebuild and needle.  First, I was wondering if there is any way to tell the approximate year of the engine, or series.  Secondly is the needle and spraybar assembly.  The spraybar has 2 holes in it 180 degrees from each other, so I put it in with one hole facing the crank, and the other straight out the venturi.  And the main question regarding the needle is the shape.  When I acquired the engine, it had a needle with a flat tip on one side of the end.  The new one was fully tapered, round with a blunt end.  Is it ok to use this needle in this engine, as I replaced the needle, spraybar, and needle 'holder/clicker'.  Anyways, thank you in advance for any and all help you may be able to provide.

[C.T. Schaefer]

It wont run that way. The holes have to be straight across. Sometimes they are offset a little. Try both ways. you should not see any holes. It has to be perfect to work correctly.  Cheers.

[Jim Kraft]

What CT said. The holes should be front and back. Either of the needles will work fine with the blunt tapered one being the easiest to set. The engine is an 80 to 87 vintage.

[Brett Buck]

It wont run that way. The holes have to be straight across. Sometimes they are offset a little. Try both ways. you should not see any holes. It has to be perfect to work correctly.  Cheers.

   It certainly WILL run that way. It will run with the spraybar in *any* orientation. That was one of the possible adjustments, rotating the spraybar to even out the inside/outside speed.

    However, I would start with the holes fore/aft as recommended above, and if the hole isn't quite centered, put the short side towards the crankshaft. Unfortunately this oriention is also by far the most critical to get right, and even tiny rotations from the ideal can have very drastic effects. Eyeballing it is very unlikely to get the magic ideal orientation, so you probably want to adjust it on the bench with very tiny movements. In the good old days when the spraybar end was round, you pretty much had to file a flat on it to get a grip and control the orientation. You have one of the later types with a hex end, which should be a lot easier.

     The round needle will probably work in the old spraybar and definitely eliminates the issue of trying to find one where the flat lines up correctly with the holes. I have only bench-run mine with the round needle, so I don't know what it does in the air.

     Brett

p.s. BTW the engine is *probably* from the mid-80s, shortly before the 40th anniversary. The fact that the exhaust face is not milled flat, and the over/under holes are not drilled out, combined with the matt-finish case are good indicators. Same with the cutaway drive washer - the mid-70's version had a big flat black-oxide type that weighed about twice what this one does. The 40th anniversary and subsequent usually came with this type, but crudely chromed.  That spraybar is from the 80's, too, so it may well be what came with it. There's no way I know to definitively pin it down, since there are no serial numbers.

[Brett Buck]

 Fox added the ears for mufflers in the early 80's, as stated.  Before that the only provision for mufflers was a centered hole in the exhaust. Fox .35 stunt engines (.29's too) had no provisions for mufflers prior to the late 70's.  I think this is about the time the AMA decreed mufflers be used. Mostly to save flying sites.

I think the first Fox engines used "Acme" needles.

  Austin-Craft, I think, and they were "universal" replacement needles that were already on the market.

    The type with the little "+ sign" on the end were really a good idea, since it relieved the issue with cantilevering the needle on the threads, which were sloppy and wore to be even sloppier every quickly, particularly with the brass spraybars.

The needle with the flat was actually a much easier to produce version of the same idea - the round part fit right into the inlet side of the spraybar and also helped keep the needle centered. When it was set right, about 1/16"-1/8" of the taper end fit into spraybar on the inlet side and kept it from moving around. That made the very sloppy fits on the threads tolerable.    That effect is lost with the "round" needle that really does just hang from the threads. The spraybars that came with those had a longer threaded section (although still not long enough) and were steel instead of brass, and fit much tighter in the threads, because they had to.

    The muffler ears (vice the over/under holes) were added in the early-mid 70's, replacing the over/under hole mounting that broke off very easily and also distorted the case, particularly when it wore a bit and the screws started bottoming out. I think the over/under holes and the (optional) mufflers to use them were first offered in the late 60's. They were being advertised in model mags (full-page ads!) in the very early 70's. The muffler ears ALSO break off, not quite as easily, and ALSO distort the case. They didn't get that right until the 50th anniversary models when they made it look like the ST46 type, which is pretty bulletproof.

   Mufflers are still not decreed by the AMA, even now. The "90 at 9" campaign started in the early 80's but the AMA never actually made a rule, it was just a strong recommendation (that many RC clubs made their own rules for). Of course noise is a complete red herring, note the story the other day about how someone called the cops on gliders!

   Brett

[Chancey Chorney]

Thank you all for the help, it is greatly appreciated.