So I bought a mostly-there Fox .35 'cause it had the prop washers I need, for about 2/3 what the parts alone would cost from Fox.
I didn't pay much attention to it, as it had no webs on the nose sides, like my '57 Stunt.
It came today - turns out it's a '57 "Silver Head" Combat Special.
And the prop driver doesn't fit (by a few thou) the Stunt shaft (I could cure that tho').
So now I have another engine needing parts!  

Anyhoo, an old engine review said it turns a 10x6 ~1000 rpm faster than the Stunt .35.
Is it suitable for stunt, maybe with another head gasket?
Will it 4-2?
Will a standard Fox NVA work (original had the spade needle)?
It's also missing the venturi insert - how will that affect the run?
Or better to sell it to someone who wants a '57 Combat Special (if there is any such being)?

Thanks.

Terry

O K  how much do you want to sell it for???

I'd like to find out more about it before I decide what to do Dave.
Also, I have no idea what it might be worth.
I will say that I have several .35 Stunts so don't necessarily care to keep it.
PM with an offer if you wish.

Terry

The definitive online Fox Combat engine history is at http://www.clcombat.info/foxhistory.html

I'm not exactly sure what you've got there, but it's not a 57 CS.  Maybe it was originally, but it's not now.  See the gap between the top of the cylinder casting and the head?  The 1957 35 CS didn't have that gap.  Generally the gap is a dead giveaway that the engine is really a Fox Rocket .40.  Given that the case has the removable venturi insert, no lugs towards the front of the case, and apparently no Rocket emblem on the bypass (since that would be really obvious), it's not an original .40 either.

Fox used the O&R type drive washer on the early stunt engines between the tapered seat and the typical Fox 4 cog drive washer, but by the time the combat engines came around they had switched over to the thick steel drivewasher.  The O&R washer will work, but the later Fox washer works better.  The prop washer isn't right for that engine either, the right one wouldn't have been knurled. 

The spade tipped needle, and for that matter the later fully tapered sport 36 needle are an endangered species.  They can be found, but not that easily.  The normal Fox stunt spray bar is too short.  The closest somewhat modern Fox nva that would fit is the big 40 assembly.  A small Supertiger nva should fit perfect without any spacers or shims. 

Your assessment is correct, just about none of the important parts interchange with the 35 stunt.  The crank didn't use a pin.  Even with the wrist pin hole, the liner has to come out before the pin can be removed.  The hole is necessary because there isn't enough room to slide the rod off the crank pin with the piston still on the other end of the rod.

So what is it?  Maybe it's a 57-62 Combat Special or Rocket 35/40, or a 29X case, with a different set of internal parts.  Someone could have dropped any of the baffle piston 36 piston/liner setups in the earlier case, which would result in a gap just like that.  There's also an early 36X thick head shim/gasket that would make the gap larger if it were installed in the earlier 35 on accident.  I don't do the .40s, but most I've seen look to have a larger gap.  Could always measure the bore and stroke.

The early Fox combat specials and derivatives aren't terrible engines.  They do like to shake, worse than a stunt 35, and they won't run like the stunt engine in a 4-2 break style.  They prefer to be run faster with a smaller prop.  The lapped piston/liner is a bit fragile, they need lots of castor and hard use is hard on them.  By far the problem I see with them is that they tend to wear.  I've got a few complete engines, and a few spare cases that all have rub marks inside the case at the bottom of the crank's throw.  The marks are from the connecting rod rubbing at BDC.  It doesn't really matter if it's from a sloppy crank bushing or an egged out rod, it's pretty much a design flaw.  There's zero spare parts support.  Fox changed the early combat engines almost yearly, a variety of Fox liners will slide into the case but most aren't exactly the same.  If you desire a stunt engine, a stunt 35 would probably work better.  If it is a .40 it might be workable with an extra head gasket, etc but it's probably not worth messing with.  If you paid less than $25 you can probably get your money back out of it on Ebay.  It might make a decent sport engine assuming it's not worn out.

For reference, here's a 1957 silver head CS, the needle is wrong but the rest of the parts are original.



1958 black head CS.



1960 red head Rocket 35 (note: I don't have a 1959 RH Rocket in my collection).



1962 silver head Rocket 35.

Thanks for your interest and input guys.
Here are more pics.
Bore/stroke are .800x.700, so it's a .35, as on the case.
Note the radii at the base of baffle, I think unique to the '57 CS.
Don't know what to say about the head/casting gap; even w/o a gasket, it has a gap.
Bypass has long tapered entry from crankcase, not stepped as on my Stunt.
Sorry, don't quite grasp the measurement you mention, Phil.
Re: the case hole, I thought that might be the case Andrew - crank throw looked noticeably longer that on the Stunt.
In 3rd pic, O&R drive washer on left, "Fox" on right - note the O&R has a circular indent; possibly an original Fox on the wrong engine?
The outer washer has a straight hole, no taper, so it's not a McCoy or other drive washer.

FWIW, I've concluded that there are plenty of .35 Stunts around, so no need to reduce the supply of CSs to try to make one.  

Learning history and details about these old engines is nearly as enjoyable to me as running/flying 'em - hope we can sort out what this one is.

Terry

Terry, With the head off, you can measure the thickness of the sleeve flange. If it measures approx. 1/16 it is a .35 sleeve. If it measures approx. 3/16, then it is a RR .40 sleeve.
I am beginning to wonder if some one put a RR .40 sleeve in it..
Fox also made a RC .40 with the tall sleeve and the .090 gap under the head.
Back in the day, an S1 Ringmaster with a CS on it was lots of fun.

Phil Bare.

I'm enjoying watching this thread. There's quite a wealth of knowledge herein, very detailed, very specific. - Excellent! 

Terry, what you have is a 1957 Silver head .35 CS.  I just went to the dungeon and checked my collection. I have an example of all but the 1958 Black Head .35 CS. All of the engines built in that case has the boss for the pressure tap.
The heads are all the same casting. Some engines, such as the .29X had machined bar stock heads and those are readily apparent.
The loose head in your first pic threw me a curve.

Phil Bare

It looks much better in the last pic, I guess the gap was just from the head bolts being loose before.  It's definitely a 57 Series I silver head Combat Special based on the pics posted.  As noted the provision for the backplate pressure tap is there on most if not all of the 4 bolt backplates.  What the history list is getting at, is the Series III came with the post milled shorter, drilled, and a tap already installed.  For the most part the rest of the early Fox combat engines came with a venturi restrictor installed and an undrilled backplate.  Fox offered the service to drill and install a tap, or a backplate with the tap installed for a few dollars.  

Here's a late Series III Fox Combat Special just for reference.



And here's a late (3rd type?) Fox Rocket 35.



You can see the family resemblance.  As Duke made changes and refined the engines, those changes often carried over to the other engines that used the same parts.  That's why there are Series III CS's with the Rocket on the bypass, and Rockets without the Rocket and with the venturi restrictor.

I've managed to assemble a fair collection of the Fox combat engines from the 57 up through the 36X's with a few small gaps.  All of mine are for using, and I've run most of them on the test stand and on vintage combat planes.  Wish I could say the Series I and II ran better than they do, but it seems that they run fine on the stand, but want to run flat out in the air, which makes them overheat, sag, and die before the tank is empty.  They might get better with more fiddling, but so far the Series III and up engines seem to work much better for me.  

Here's one more shot, a chronological line up from the 1957 at the back left, up through the MK III and MK IV in the front.  Notably absent are the first version Rocket Red Head, the middle version of the Series III, the straight plug first version 36X (since added), the mysterious MK I, MK VI, and MK VII.  I intentionally have avoided the 29s, 40s, and RC versions as it's bad enough just trying to keep the Combats straight.

Nice collection, Andrew, you wouldn't happen to have an extra Black Head that you would part with, would you?

Regards, Phil Bare

The weather's still NG for bench running, so while waiting I've been researching.

Here: http://www.craftsmanshipmuseum.com/Fox.htm, by Duke Fox I found:

"About this time combat model flying started to become a recognized event. It was obvious to me that if I wanted to retain any part of this market, I had to come up with a better motor than our stunt .35. The motor that we settled on was a production version of a hand built motor that I had built back in 1954. The hand built motor was made primarily to explore the idea of making a fuel pump in the crankshaft. The fuel pump idea never did work, but the motor itself ran quite strong. The prototype I still have, and it runs quite strong, even by today’s standards. It was a .36 size motor, was a single bypass baffle design, except the baffle was curved in the manner of the Bunch tiger. The crankshaft diameter was increased from 7/16" to 1/2", and the rod was somewhat sturdier.

I made up production drawings and had tools made to make what became our X series of motors. In retrospect, I feel that I made a mistake in not putting the extra effort into making curved baffles for all the pistons, but this was a little more expensive than cutting a straight baffle. On the production motor I went to a straight baffle for economy sake. All of the nice, docile handling characteristics of my prototype went down the drain. The straight baffle version was just plain cranky. I made and sold a few hundred of these, but I could see that this was never going to become popular unless I did something about the crankiness. I did experiment and came up with a higher, different shaped straight baffle that became the black head combat. I still don’t understand why I was so hung up on the straight baffle. It still didn’t run quite as strong and act as nice as the prototype. However, this motor did sell and became the first of a long series through about 1971 or 1972, when the series was discontinued."

I'm not familiar with the Bunch Tiger, and it's just a matter of curiosity but is the "curved baffle" design that of the '57 CS's radiused base or an earlier baffle actually arced in some plane?

And his note of docile vs cranky makes me wonder which the '57 is:
 "The straight baffle version was just plain cranky. I made and sold a few hundred of these, but I could see that this was never going to become popular unless I did something about the crankiness. I did experiment and came up with a higher, different shaped straight baffle that became the black head combat."
Is the '57 the cranky one or simply part of a process that "became the blackhead combat", out in '58?

Terry

Thanks Andrew -

I'm wondering if the '57s were the "few hundred" or if he refers to a "pre-'57 Series" series.
"Rare" isn't necessarily "Valuable" but it is "Funner"!  

Addendum: Would you, or maybe Phil Bare, post comparative shots of original prop washer pairs?
Or a link to some, if known.
I'm not dead-set on original but it'd be nice to have, if I knew what to look for.

Terry

Well alrighty then.
I'm out of questions now. 

Thanks Phil.

regards,

Terry

Generally speaking, the Fox Combat engines from the 57 CS up through the 36X used the same prop and drive washer as the Fox 35 stunt of the same period. 
Bill Mohrbacher's illustrated history of the Fox 35 - http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=323889 is a good guide.  By taking the year of the engine from http://www.clcombat.info/foxhistory.html the same year 35 picture would show the most likely washer.

The only exception I can think of, is that some of the Rockets seem to have come with a hardware store type, generic flat washer for the prop washer. 

I only have 1.3 megapixel to work with, and a flash that washes out most detail, but here's the type washers used in 57.  Sometime in the Series III production (60-62) Fox stop blackening the washers.  The style didn't change until the 36X got the grooved drive washer.

It's hard to see in the picture, but the back of the prop washer is relieved around the crankshaft stud, about the same diameter as the part of the drive washer that's not knurled.  The front of the prop washer may be relieved on some, and they can be dented in if over-torqued. 

It might show up better on the natural steel version...
The knurled prop washer set is from a Blue Ribbon special, the smooth prop washer set is from a 35X.

Hey, Terry
Glad that the NVA got you going.

Regards, Phil.

Well, alrighty then! 
Thanks Bill.
Never ran across that baffle design, and it's just a matter of curiosity, but your pictures make it perfectly clear.

Terry