What size engine do I have??

[YellowJacket]

I just spent a weekend helping my beloved Uncle who is a disabled vet (and avid model airplane junkie who is responsible for my own love of this hobby) and as I was walking out to take my to the airport, he gave me an an airplane engine. This is a Fox that looks new and unused, but is clearly not a .35, has an r/c carb, and looks to be 40 size.  The problem is that there are no markings on it other than “Fox”.

Is there a way I can tell what size and type of engine this is without taking it apart and having to find gaskets that probably don’t exist anymore?

I would like to put it in my yet to be built Sig Super Chipmunk, and hopefully find a compatible C/L Venturi for it.

Thank you for your help and if pictures are needed, I can take some when I get back to Texas tonight.

Greg

[Dave_Trible]

Does it have a slanted glow plug?  Duke made a particular series of engines from parts from a failed combat motor in a .29 and .36 size with the same case, both in CL and RC. This case is the size of many light .40s.  Before that he also made a stunt .40 (early -mid 70's) that may not have markings.  Some of those could be RC.  I know the slant plug motor actually runs nicely and exhibits none of the vibration issues that was said to be the demise of the combat engine.  This would pull your Chipmunk like a champ.  Lee Machine shop can fix you up with a venturi and a muffler if you choose.  I have none of mine any more but I think the .29 was stamped to that affect someplace on the motor.  The .36 had no marks-could be the other way around.
BTW these would have a bolt on venturi or carb-NOT a square cast venturi.
Dave

[kenneth cook]

               There were two variants in the slant plug design with features that you mention. That would be the .29 and .36. These were available in a shiny case and a bead blasted version. Both versions used the same size case. These had a four bolt backplate. The. 29 is stamped onto one of the lugs if it's a .29, the .36 had nothing other than Fox. Both of these engines had two casing boss's which was threaded (2-56)  in the center of the exhaust stack which is known as the over and under mounting.

[qaz049]

This is the .29 version though the .36 looks exactly the same.

[YellowJacket]

Here are the pics of this engine...

[afml]

Fox 40
Good luck with the Chipmunk & "Tight Lines!"
Wes

[YellowJacket]

Oh that’s great news!  At the risk of overwhelming you with follow-up questions, these things came to mind and I need to figure these things out so I feel confident with this awesome motor:

So that I understand it’s history and relative technologically advanced design, do you happen to know if this engine was produced late in the Fox engine production timeline and incorporated anything like ball bearings?

Is it like other Foxes that have bushings for main bearings and requires 30% all castor oil?

Is there a particular size prop that it likes?

Since it looks new, I will have to put this on a test stand and break it in.  Should I use a different prop and fuel for break-in?

Is there any “pre” break-in procedure to loosen the components up that I must perform (like a frozen ring??)

Any unusual break-in procedure recommended or just run it rich for 5 minutes or so and let it cool completely, then get about an hour of time on it this way?

These questions must surely annoy but I do give my word that one day when I am sage, will gladly
pass my knowledge on to others.  Thank you!

[goozgog]

Hello YellowJacket,

   You're not annoying anyone.

  This is a forum for exchanging
information about Control Line flying.
There is a mountain of help and
knowledge here and if it doesn't
get shared it would be useless.

Ask all the questions you want.
99% of us are pleased that you're here. 

Cheers! - K.

[YellowJacket]

Many thanks Keith!

I just want to make sure people here know I am appreciative of their time and guidance while I build my own knowledge base.

[Ron Cribbs]

Greg,

30% oil is way too much. Not sure where you heard that.

There will be a lot of differing opinions and you already know about mine (GMA 10-22)

There is a point where too much oil is a bad thing. Kind of like sucking Maple Syrup through a straw. Most common recommendations for Fox’s of most types are 29% oil, that’s what Duke recommended as well.

Time has moved on and we now know more. Many people use 22-25% oil without any problems. Myself included.

Ron

[YellowJacket]

Hi there Ron!

Thank you for that information.  That works out nicely so I can still keep just two formulations 1) 10/22 for the 25 FP, and 2) 10/22 plus 10 oz castor to bring to 28% for my McCoy and Fox.

[YellowJacket]

Thanks Motorman, but the fact that my uncle gave it to me is the soft spot I have for it.

So it sounds like I have most of my questions answered:

1) fuel is 28% oil
2) use an 11x6 prop
3) probably has a ball bearing

The only questions left to answer are:
1) any particular break in procedure?
2) any concern for stuck rings or anything else to be “unfrozen” prior to firing it up?
3) approximate years this was in production and any particulars about its behavior?

[Robert Zambelli]

Hi, YJ.
This engine has been around for quite a while.
When I spent a week in Muncie with George Aldrich, he told me quite a bit about it.
It was a joint effort for him and Duke Fox, originally designed as a stunt engine and later offered in a R/C version.
He said that it ran smooth and loud but didn't make much more power than the Fox Stunt 35.
Regarding the fuel, I have a few engines like yours but have never run them so I cannot recommend a proper fuel blend.
For what it's worth, I have run many other Foxes, mostly from the 50s.
19, 25, 29 and 35. Many have well over 1000 flights on them.
Some were purchased new, others used.
I have never used more than 23% oil, 50/50 blend and 10% nitro.
Most are/were run in a 2-4-2 style but a few were run screaming lean.
NEVER had one break or wear out.

Motorman makes a good suggestion - you're probably better off with a Brodak or OS powerplant.

[YellowJacket]

Robert, that is a good piece of information.

So maybe I will go down to 25% oil to run with the McCoy as there are so many opinions on the older engines, but Ron swears by the VP 10/22, so I will make it easier on myself and just add 5 oz of Sig castor to 25% total oil.

Do you think an hour of running time on the bench is good?  If so, what is the longest run time you recommend between cooling cycles to get that 1 hour?

[Mike Anderson]

Thanks Motorman, but the fact that my uncle gave it to me is the soft spot I have for it.

So it sounds like I have most of my questions answered:

1) fuel is 28% oil
2) use an 11x6 prop
3) probably has a ball bearing

The only questions left to answer are:
1) any particular break in procedure?
2) any concern for stuck rings or anything else to be “unfrozen” prior to firing it up?
3) approximate years this was in production and any particulars about its behavior?

Plain bearing engine.  And no rings to stick.  They came out in the early '70s and weren't in production for very long.  I think it was 1973 when I bought one and that was fairly early in the production run.  I doubt they were made past 1976 or so but don't have any old magazines anymore to see if they were in the Fox ads.  I bought it in a hobby shop and I think it cost 17.99.  Break in is the normal Fox type for plain bearing, non-ringed engines with rich runs, smaller prop,  until it holds a setting. Finish breaking it in on a plane. If you are going to change it to a control line version, they came with a venturi insert that sleeved it down.  But the venturi was cast into the case, not a slip in in place of the RC carb.  We changed them to OS needle valve/spray bar assemblies.  I don't think I ever used more than 25% oil, but you definitely want it mostly castor.  Sig 10% nitro, 25% castor or equivalent would be fine.

They make power on a par with K&B .40's, or Enya 40's from the same period.  There was no muffler but I had a home-made one that didn't rob too much power.  I would agree that an 11-6, 11-5 would be good start.  I actually flew mine mostly with the old Top Flite paddle blade 12-4 woods. 

[RknRusty]

Even though it looks new, I'd like to offer the following tip, just in case:
On engines that have sat for a long time, I like to remove the backplate and make sure the rod slides freely back and forth on the piston's wristpin. They can get castor-glued together, and that will egg out the holes in the side of the piston. If it is stuck, I invert it and fill the piston with WD40 or penetrating oil, and heat it until I can move it back and forth with an allen key or hemostats.

Rusty

[Robert Whitley]

Be aware that the Fox 40 has a wider case than the 35 that the Sig Chipmunks were designed for.
I’m at the final stages of a rebuild on my 1974 Chipmunk with the Fox 40 and I built a more modern crutch system this time around. I also widened the fuselage a bit to better accomadate this engine, otherwise you will need to carve the engine bearers to fit the additional case width.

The engine is also somewhat thirstier so plan on a larger fuel tank.

I will try to find some time to post pictures in the next few days.

Cheers and good luck.

[YellowJacket]

Wow, excellent information Robert, Rusty and Mike!

So, now I know it’s history, design and relative place in Fox folklore.

I also now know that I have to widen my fuse a little to accommodate it as I do t want to remove wood from those already thin, hardwood motor mounts that kits always come with.

And will break it in with a 10x6 prop I happen to have for my McCoy then acquire some 11x6s for using on this Fox 40.

But now, just a tad more help please on technical jargon...I am mechanically inclined, so don’t worry about that, it’s just that I don’t know all the terms for the smallest engine components yet.  I do know: case, cylinder/cylinder sleeve,  head, head gasket, head screws, back plate, back plate gasket, back plate screws, crank shaft, piston, piston rod (assuming that is the same as connecting rod that I read here often referred to as “con rod” but I don’t know:

if a “wrist pin” is the circular end of the piston rod that connects to the crank shaft or if it is the little pin that bisects the piston and holds the piston rod to the piston.

I listed all the components I could think of from memory so hopefully I did not leave much out (carbs and Venturi components notwithstanding) and I can just get these two pins sorted out in my head.

Also, can I reuse the old gasket when I remove the back plate or cut a new one from thick grocery store bag palate as was previously advised for doing surgery on my McCoys?

Again, many thanks!

[Brett Buck]

if a “wrist pin” is the circular end of the piston rod that connects to the crank shaft or if it is the little pin that bisects the piston and holds the piston rod to the piston.

  The latter- the pin that goes through the piston. It's called a gudgeon pin by foreigners.

   The issue with it is that even if you make an effort to put some sort of oil in the engine after you run it, it's hard to get anything on the wrist pin and to displace the castor oil (which is required in great abundance on this engine), so it tends to glue itself to the piston and/or connecting rod.

     Brett

[Robert Whitley]

With regard to a muffler to fit the Fox40, I am going to use a Dubro tongue muffler on mine.
It fits on just fine.
I only have one factory muffler but the extension stock is still readily available for under $10.00 and can be easily cut to any lenghth you wish. It will require baffles and end plates which I am having locally made from stainless steel with a waterjet cutter. The bolts and spacer washers are just commonly available 4-40 hardware and the engine attachment is a narrow worm gear hose clamp around the cylinder body.

You will be able to make four mufflers from one lenghth of extension stock.

When I get the baffles from the fabrication shop I will post some pics for you.

[YellowJacket]

Robert, I am so glad you mentioned that about the muffler! I need to get the exhaust out of the cowling of the Chipmunk and I want to look good. 

So yes, I would greatly appreciate pics and bill of materials to get this done and if possible, the vendors that I can acquire them.

Please PM me if you prefer but I would really like to put this together.

Do you have a carb on yours like I do and if so, do you just wire it fully open?

Someone a while back mentioned “Lees Machine  Shop” for a Venturi as well as an OS max configuration fitting it.

Thoughts?

Greg 

 

[Robert Whitley]

Hi Greg,
Mine is an original control line stunt model so the venturi housing is cast into the case and it came with two different size venturi inserts.

Definitely check with Lee about an adaptor or find another carb you can sacrifice and gut it to put a fixed venturi in or like you suggested just wire your carb wide open.

The weather has finally improved up here in Canada so I will likely not be able to gather and post pics for a few days. I teach flying so I need to work when the weather gods let me.

This time around on the Chippy rebuild I will be painting it up as a real one that I have flown.

[Air Ministry .]

This Chipmonk has that Fox 40 . ( the pommy drg. shows Super Tigre / later ) .



Thisisthe control line intake .



Some rubbish on a resurection here : http://sticksandtissue.yolasite.com/resources/2013/ST77.pdf

If you havnt got that far , a few inches on the span , fore & aft , wouldnt hurt .

[YellowJacket]

Mat, that is a neat looking chipmunk but can't make out the fine print.

I will be building Sig's version but would love to get a copy of those plans you showed so I can get some ideas about possible improvement on the Sig.  Is it possible to get a copy somewhere?

Thank you,

Greg

[Mike Anderson]

I see two possible complications with converting this engine -

1. How is the carb retained in the crankcase?  I don't see any set screws or clinch mechanism.  If it is glued in, there isn't much real-estate to install set screws but one might be able to fix it with adhesive.

2. As to the muffler or exhaust extension, that rotating baffle is going to be a problem.  Removing it will leave very large holes that will be difficult to plug.  If you leave it in (and perhaps file it down so it doesn't interfere with a strap-on muffler of some sort), you'll want to have some method of fixing it so it can't rotate into a closed position, if the carb is removed.  I think the old DuBro Muffleair used to come in a version that had a couple of plugs (that fit K&B .40's) to plug those holes that were retained by the muffler straps.

EDIT -- Just got to looking at the pix again.  Is it possible that the carb body is part of the casting?  That would make converting a REAL headache.

[YellowJacket]

Mike, I am learning more each day and to your point, there is no way to convert this baby.
I was just emailing with Jim of Lee Machine shop and he told me pretty much the same thing that I can’t convert it due to different things being cast in for each version...so he said I will have to wire it fully open.

I also spoke today with Jack at Brodak who also owns one of these and he will call me next week about a tongue muffler he might be able to fabricate for it so I can get the exhaust outside the nice fiberglass cowl of the Chipmunk.

But I would not have more knowledge now if it were easy and conversation not being had about each little challenge, and for that I am grateful 

[Ed W. Prohaska]

The plan posted above is Pete Tindal's Chipmonk 9 published in April, 1977. Wing span is 57". The AMA Plan Service lists them for $14.00. There is probably an extra charge for postage. They recommend you buy a second plan for half price so you have a pristine copy for reference while the one you build on gets destroyed. Good idea!

[Air Ministry .]

This ones forsale in classifieds at the moment . And Frank McCune was recently venting about one in the engine set ups . Maybe He'd part with it ? .



Id thought the intake screwed in . dunno . Seen pictures of them like that . Aftermarket or differant series ? ? .

Cut off at the step & polished threaded straight tube , same dimensions , into the case .  Need stripping to do it .

Theresa bitoff info on Tindalls Chipmonk here . https://stunthanger.com/smf/building-techniques/sig-super-chipmunk-19826/msg199962/#msg199962

His was spelt differant ,  Theres thousnda here ChipmUnk & ChipmOnk , in SEARCH . as is there for FOX 40 ! .

Tindalls was published in the U S & in the U K , Aeromodellor .  Same lengthy artical . Mentions is a development of Jim Van Loo's Chipmunk .

Heres the aeromudler with it , Ive gotta copy of the srtical if youve gottan address ( P M ) of theres more than a few on Ebay . Which'd be quicker .



He also did a ' finishing ' artical in Aeromudler , will check the date , as its the same plane . Always wondered How it'd be with the ' Canada ' Bubble Hood ,
Like Art Schoals .  Also check your P Ms ! ..