Cox Venom Piston Rod Reset Question

rscarawa wrote:

Cribbs74 wrote:Possibly Eric, but not always. If the rod had been pounding the bottom of the piston a good while it creates excess space, In that case the reset will lessen or completely remove the SPI.

If that is the case, I should be able to measure from the top of the piston to the bottom of the rod to get an idea how sunk in that rod is.  Does such a dimension exist to compare against?

I am not sure if it is the wear of the piston bottom that increases the socket play, and not the socket opening up a bit, allowing the ball more free-play.....the varnish depositing inside the socket in fact separates the metal surfaces i.e. the ball end of the rod from the bottom of the socket so I would not expect major wear inside the socket.

If I am correct it means that even if the socket is already lose, the piston-rod unit does not change its length when the ball touches the piston bottom inside the socket..

Not that it will answer all your questions, but still a great place to just learn about all the Cox engines...
http://www.mh-aerotools.de/airfoils/cox_frameset.htm

You are playing about both ends of the spectrum with the Venom and Texaco

look at the Texaco event to see what was intended... I was amazed at the Size propellers they make work for than Cox Engine configuration

back to the Speedsters... many of us find that each engine has an ideal prop diameter/ pitch that works well on the bench and that size might change significantly in the air -----mostly due to model weight and drag

An other consideration to Prop diameter and Pitch is the construction... soft black plastic has lots of flex and pitch reduction
Grey harder not so much pitch change at RPM
Wood Vs Nylon
Shape

Find Amp Abuser...I think he has more prop testing and advice for the go fast stuff (cox, fuji, Picco, etc)

I might add that Fuel plays a bigger role in these dinky motors... Nitro and OIL content changes are much more pronounced in the .049/.051s than in .15s .20s and .35 engines

I find the best consistency is with my home blend ...basically a copy of Sig Champion 25% N 1/2A blend

I can change the fuel down to 15%N or up to 35% N and NOT see enough of a difference on the Tach

15%N is harder to start and does NOT have as broad a Needle range ( touchy)
35%N is great but NO real significant RPM gain + 200~400 over 25%

Lots of folks believe 25~28% ALL Castor is needed---
I blend now to 22~23% 50/50* Oil and although I do not put hundreds of hours on these Cox engines, I see no real wear like in the 70s when we ran them all the time on "Whatever we Had" fuel

*50% Sig Castor
50% Klotz Synthetic

BTW when you have a prop with a too loose prop Hole for the bolt/screw---- You can usually find a diameter of fuel line to act as the spacer between the Bolt/screw and hub ID that will work just fine for centering the prop to crankshaft...occasionally I have to increase the prop ID for the fuel line "spacer" over the Bolt/screw to work

I like that idea of spacing the prop with fuel line. I will give that a shot.

I did find that running 28-30% oil vs 20% on 20% nitro seemed to yield no RPM change with my 6x3 prop tests on any engine. I think I will mix my gallon up to 22% as that seems to be a common recommendation.

The challenge with choosing the right motor is an odd one. First, I am playing around the lower end of the power requirement for this plane. So is it better to have more power output with a smaller diameter prop or have less power and more prop? I can see arguments for both but testing will tell. In the past, I have seen value in a larger prop as you get more of your thrust away from the plane. I will also have to put a chin fairing in to keep some of the prop blast off of the firewall as this type of blast wastes power.


Thx for the recommendation.

I did try to make my BW emulate a Texaco motor by playing around with compression and turning an 8x4 APC Thin Electric prop. I had heard of people running that prop on their motors but my BW did not like it no matter what I did. The best I could do was 7100 rpm. Seems too low as I would like to be in the 9000-10,000 range.

I did stop by that German site devoted to Cox. Nice history of motors there.

Check out this page I found

a bit dated but good hints

http://scamps.homestead.com/Texaco_Secrets.pdf

That is a good article. By comparison, my Cloud Ranger should come in under the weight of the described model and with less wing area by a good margin. That means that using an 049 should be viable for this project.

I've enjoyed reading this thread. It's always interesting when someone asks a question about an engine's performance. There always seems to be something to take/learn/consider from the commentary. I'll admit that I've never owned a Cox Venom but I agree with Ron on installing a new reed to re-establish a baseline. The reed-function is crucial. Not sure what reed-system (reed and retainer style) your Venom came with.. but replacement-reeds can vary in thickness by as much as .009" governed by the material used. The older Copper 4-legged star reeds are .001". My Steel (oval) reeds are .002", Mylar (oval and Mylar-star) are .005" and Teflon (oval) are .010". Cox switched the reed-retainer in later years, from a wire circlip.. to a plastic-cap/ring. The cap-style seems to be gapped to use the .005" oval Mylar reed. If your reed-retainer is a wire circlip.. be sure that it doesn't pinch the replacement-reed. Some people thin-out their wire-clips by rubbing on fine sandpaper if they're using a thicker reed. Example; an engine originally having a thin (.001") Copper reed.. being swapped to a .005" Mylar. That thicker reed is going to fit tighter and possibly be pinched when the retainer-clip is installed. Many people (including myself) check the reed-function once installed, by gently sucking and blowing air (with your mouth) on the reed-housing. Sucking should open the reed-valve with little resistance, while blowing should close it with a noticeable sealing-action. It shouldn't "squeak" or whistle. The seat must be clean and smooth. An old reed could have been stuck to the seat from non-use.. (gummed-fuel) which could still be fouling the seat. I use a Q-tip/cotton-swab with solvent to clean the seat before installing a reed. It can take a bit of rubbing sometimes.. and maybe more than one Q-tip, but it's a safe way to avoid scratching the seat. It's really an important area of concern when and if an engine suddenly doesn't run right. A speck of grit or even tiny seeds can be sucked-in through the rear air-intake.. and get caught under the reed. The little mesh-screen helps to prevent this for the most part.. but some people remove them for more airflow. Your Venom has a larger (.082") opening at the air-intake.. and leaving the screen in place is even more important IMO.

I'm partial to running fuel with 25% nitro at least, in my Cox engines. Where your PowerMaster does have the correct oil.. it's short on the nitro that makes these engines run their best. If you do business with "Sig", they have excellent fuel. Their "Champion" blends are available in 25% and 35% nitro and have a 50/50 mix of castor/synthetic oil. It's available in pints and quarts too. It's better IMO.. to buy/keep 1/2A fuel in smaller containers. Running your 1/2A's on low-nitro fuel from (for example) a gallon-jug, could cause trouble.. depending on how fresh the fuel is.. and how soon you can use it up. Your 8cc Venom tank is approx. 1/3oz. A pint of fuel should give you at least 45 runs.. including exhaust-primes. A quart; over 90 runs. Even running a 1oz. external-tank in an RC model will take 128 runs to go through a gallon. Where the Cox engines use so little fuel.. it makes more sense to me, to buy fuel in smaller bottles. Sometimes fuel will go stale.. which can REALLY affect these little engines. You can always use that up in your less-sensitive larger displacement engines.. or for a good soaking-solvent.  

Be careful with the piston (and cylinder..) assuming that it's OEM. You may know that an original uses a lightened piston. The piston; as with most Cox pistons, I believe is one-piece.. (less the con-rod) and has a Copper-plated top. I believe the lightening-process involved removing material from the inside of the lower skirt.

Something to try for running the Venom on the Herr RC model, is running a Cox "black" 6 x 2 prop rather than the 6 x 3. It's a L/H prop.. but the Venom will run equally well in either direction as all cox reed-valve engines will. This would satisfy your concerns of keeping the blade-area outside the fuse.. and also unload the engine more than a 6 x 3. Just be sure to trim for an opposite torque-roll on your maiden.

Good stuff! I have a NIB Herr "Little Extra" ARF.. and also a NIB Ace "All-Star" Bipe kit.. but I've never flown RC.. and neither are beginners models.. especially the Little Extra. My only RC engine is a NIB OS .10 FP which would be ideal for either of them.

Thank you for the advice.

The reed retainer is one of those plastic jobs. For that, do you recommend the Mylar reed? That is what it came with and it has now. Is one reed retainer style better than another?

I will look for a 6x2 prop. I should probably try many 6x3 and 6x2 props as the pitch is frequently inaccurate. Some 6x3 might be 6x3.25 or 6x2.75. It would be nice if they had varying pitch props like they used to for 4 strokes. Something like a 6x1.5-3 where it was a 1.5 pitch at the root and 3 pitch at the tip. That would keep from wasting so much thrust against the fuselage.

I also have a tank extender on this motor. If I keep it on there, I will need to make sure it is drilled to .082 as well. I am sure it is not at that spec at the moment. That does not help things. I assume the longer intake runner also has a perf cost of some amount.

I hear what you are saying about buying in smaller quantities. Truth be told, I bought the gallon mostly for the can. My old gallon can is looking nasty and wanted to replace it. Cans work out better in my RC flightboxes. I will look into the Champion fuel though.


Thx Scot

I have both LH and RH snapstarters so either rotation is an option for me.

rscarawa wrote:Thank you for the advice.  

The reed retainer is one of those plastic jobs.  For that, do you recommend the Mylar reed?  That is what it came with and it has now.  Is one reed retainer style better than another?

I will look for a 6x2 prop.  I should probably try many 6x3 and 6x2 props as the pitch is frequently inaccurate.  Some 6x3 might be 6x3.25 or 6x2.75.  It would be nice if they had varying pitch props like they used to for 4 strokes.  Something like a 6x1.5-3  where it was a 1.5 pitch at the root and 3 pitch at the tip.  That would keep from wasting so much thrust against the fuselage.

I also have a tank extender on this motor.  If I keep it on there, I will need to make sure it is drilled to .082 as well.  I am sure it is not at that spec at the moment.  That does not help things.  I assume the longer intake runner also has a perf cost of some amount.

I hear what you are saying about buying in smaller quantities.  Truth be told, I bought the gallon mostly for the can.  My old gallon can is looking nasty and wanted to replace it.  Cans work out better in my RC flightboxes.  I will look into the Champion fuel though.


Thx   Scot

I have both LH and RH snapstarters so either rotation is an option for me.

Hi Scot, Yes.. I'd try a new Mylar reed for sure. Keep all the associated parts/surfaces as clean as possible.. and recheck before final assembly. Both style retainers work equally well. There's less guesswork required with the cap-style using the .005" Mylar reed.. where the older clip-style may require thinning the clip as I mentioned. A while back I measured my circlips' wire-diameters.. and was surprised..





.005" variance. Cox started using the thicker Mylar reed before it changed the retainer-design to a cap.. and may have reduced the wire-size to compensate. It's just a theory I have. Also.. their later plastic "horseshoe" backplates seem like a cheaper plastic. I have two that cracked-open where the clip seats. This likely led Cox to redesign the reed-holder.

The Cox 6 x 2 L/H prop is not being currently produced, as far as I know. It was standard issue on their PT19 Flight Trainer. They are out there though. A flying-buddy having a Cox PT19 might have extra props. If there's any older-established hobby shops in your area.. ask the "owner" if they have anything Cox-Hobbies related. Chances are they might have replacement-props for the most popular airplane that Cox built. You might also find some other Cox-treasures.. you just never know.

The tank-extender as you said; is likely the smaller/std. Bee .062" ID, which is literally choking-away the benefits of all the other high-performance features of the engine. I personally wouldn't use it on that engine. It can be hard enough to get a single tank-bowl to seal. You also need two venturi-gaskets for a tank-extender I believe. If there's anything a high-performance engine "doesn't need".. it's added variables when it won't run right.

Best of luck!

Hi Scott sorry I'm just getting back to you about the prop  I use is a Master Air Screw they make a  good-quality prop.MA makes a 6X2 and APC also makes a 6X2, with a APC you may need to use a piece of fuel line tubing or an adapter. If you have a new in the box Texaco engine, it comes with an adapter remove the prop screw and you'll see it.Kavan made two types of  tank extenders one for babe bee and one for a black widow golden bee (.08cc)type tank. From your description you have the correct tank extender and they do work, I use mine all the time with no problems. If you look at the link that was posted on Texaco competition you could probably build an engine with the parts available, the main difference would be using a  Texaco type of glow head.One reason people switched out the star shaped reeds for the Mylar reeds is that at the higher rpms,18K the star reeds tend to 'float'.Basically the Venom was designed as a racing engine whereas the Texaco was designed as a duration engine,lower rpm,lower compression,cooler temperature.Hope this info helps.

P-40
Thx for the update. I am just looking at what I got and how I can adapt it to work with my current project. When I started this plane, I had two .049 engines and I had no idea where they were. I had not seen them in 15+ years. The reason for doing this was more of a tribute to the Cox engine due to its history and economy. I saw a video online of people throttling the 049 and I was super impressed with how they got it to run. So I embarked on this project and did think I would find those old motors again. So I bought a couple 049s online, then a few more, then a few more . It became a bit of an illness. Then I found my old motors. I am knee deep in 049 right now to where I will plan another plane for later in 2017. I am thinking GLH.

Anyhow, I am evaluating candidate engine health and how it will work with the Cloud Ranger at the moment. Not sure if high power and small prop or low power and large prop will work best. It will require some testing once I know the state of my engines. The new servos arrived so I am resuming my wing build. I should have the wings together by the end of next week and the fuse is built. Did I mention floats? This should be fun!

FYI,
Here is the state of my airframe.  Waiting on parts to come in to proceed.

Cloud Ranger


https://servimg.com/view/19596619/2

roddie wrote:

rscarawa wrote:Thank you for the advice.  

The reed retainer is one of those plastic jobs.  For that, do you recommend the Mylar reed?  That is what it came with and it has now.  Is one reed retainer style better than another?

I will look for a 6x2 prop.  I should probably try many 6x3 and 6x2 props as the pitch is frequently inaccurate.  Some 6x3 might be 6x3.25 or 6x2.75.  It would be nice if they had varying pitch props like they used to for 4 strokes.  Something like a 6x1.5-3  where it was a 1.5 pitch at the root and 3 pitch at the tip.  That would keep from wasting so much thrust against the fuselage.

I also have a tank extender on this motor.  If I keep it on there, I will need to make sure it is drilled to .082 as well.  I am sure it is not at that spec at the moment.  That does not help things.  I assume the longer intake runner also has a perf cost of some amount.

I hear what you are saying about buying in smaller quantities.  Truth be told, I bought the gallon mostly for the can.  My old gallon can is looking nasty and wanted to replace it.  Cans work out better in my RC flightboxes.  I will look into the Champion fuel though.


Thx   Scot

I have both LH and RH snapstarters so either rotation is an option for me.

Hi Scot, Yes.. I'd try a new Mylar reed for sure. Keep all the associated parts/surfaces as clean as possible.. and recheck before final assembly. Both style retainers work equally well. There's less guesswork required with the cap-style using the .005" Mylar reed.. where the older clip-style may require thinning the clip as I mentioned. A while back I measured my circlips' wire-diameters.. and was surprised..





.005" variance. Cox started using the thicker Mylar reed before it changed the retainer-design to a cap.. and may have reduced the wire-size to compensate. It's just a theory I have. Also.. their later plastic "horseshoe" backplates seem like a cheaper plastic. I have two that cracked-open where the clip seats. This likely led Cox to redesign the reed-holder.

The Cox 6 x 2 L/H prop is not being currently produced, as far as I know. It was standard issue on their PT19 Flight Trainer. They are out there though. A flying-buddy having a Cox PT19 might have extra props. If there's any older-established hobby shops in your area.. ask the "owner" if they have anything Cox-Hobbies related. Chances are they might have replacement-props for the most popular airplane that Cox built. You might also find some other Cox-treasures.. you just never know.

The tank-extender as you said; is likely the smaller/std. Bee .062" ID, which is literally choking-away the benefits of all the other high-performance features of the engine. I personally wouldn't use it on that engine. It can be hard enough to get a single tank-bowl to seal. You also need two venturi-gaskets for a tank-extender I believe. If there's anything a high-performance engine "doesn't need".. it's added variables when it won't run right.

Best of luck!

Hi Roddie, it's very interesting all the comment you make. I am very surprised by the large number of variables that make a Cox engine work well, regular or poorly, or do not work directly. I think Cox, I reach almost every corner of the world, what happens is that many people left because of lack of knowledge for the proper functioning of them.
Today that I have taken up the theme of the Cox engines, I am overwhelmed by the number of variables that can happen in a single engine so that the result is very good or disastrous.
I fully agree with you that the valve assembly and retention ring are a vital point in all engines that have this system, as even the Pee Wee .020, the latter is much more critical - delicate - even though the line Of the 0.049.
I remain attentive to such good information! Regards....

I agree. I flew RC starting the middle 80's and you rarely saw a Cox engine. When you did, you saw a lot of issues with consistency at run time. The other reason was their engines were small and the hardware to make a well flying plane of the 049 size was expensive and not very good. Most affordable hw was geared around the 40-60 size plane at the time. The issue with reliability had a lot to do with the complexity of the induction system for reed valve systems and the fact we did not have the network of help on how to make them work. The control line people and RC people were in vastly different circles. At the time, OS was the premier motor. So reliable and trouble free. Mount the engine and minor tuning and it ran well for years. I think if we had the lower priced micro servos, batteries, rx then that we have now as well as the support of forums like these, they motors would have been more viable in the RC community. I have no doubts that the CL folks had the kinks worked out back then but we were rarely in social contact with eachother.

MauricioB wrote:

Hi Roddie, it's very interesting all the comment you make. I am very surprised by the large number of variables that make a Cox engine work well, regular or poorly, or do not work directly. I think Cox, I reach almost every corner of the world, what happens is that many people left because of lack of knowledge for the proper functioning of them.
Today that I have taken up the theme of the Cox engines, I am overwhelmed by the number of variables that can happen in a single engine so that the result is very good or disastrous.
I fully agree with you that the valve assembly and retention ring are a vital point in all engines that have this system, as even the Pee Wee .020, the latter is much more critical - delicate - even though the line Of the 0.049.
I remain attentive to such good information! Regards....

Hi Mauricio, Yes.. it is interesting to learn about more ways to get consistent or "better" performance from the Cox engines. I found that installing "larger" fuel line for an external tank, helped to get fuel to draw through the line using a "Killer-Bee" (large venturi) backplate on a suction-only feed. This might help the Tee Dee to draw fuel better too.

I made "compression-fittings" to squeeze the ends of the fuel-line smaller.. for a tight-fit on the smaller NVA nipple/tank fittings.




Smaller line was developing "air-bubbles" when the engine ran-off the exhaust-prime. This cured that issue.

Nice looking Cloud Ranger Scot, Did you every get a chance to run the RE-Set Venom ? or did the cold set in on you ....

I reset it and ran it. Still needs more power. I think I need to test it with the tank extension off. I think that is limiting airflow. Adding one of those aftermarket glowheads does seem to boost power by 500 or so rpm.

Got most of the Cloud Ranger covered. I got the vertical fin all jacked up. The rudder runs from the vertical fin to the Fuselage to the ventral fin. While I have the horizontal stabilizer square to the wing and vertical fin, the fin is not perpendicular to the fuselage by a bit. Normally when I square up a plane, I use the wing saddle as the datum. I install the horizontal stab first and make sure it is level to the wing and square to the fuse. Then I put the fin on last. I do that since most people say not to alter the wing saddle. Well, I guess the wing saddle is not square to the fuse and that cascaded to the fin not being perfectly vertical. I got it covered up pretty good with a monokote hing but still hated to see that bad alignment.

I still need to cover the ailerons and wire the plane up. If weather permits, I should be able to do a test flight in a week.

https://drive.google.com/open?id=0B_rKS7jwgyK3ay1uNmdIRG5XSk0

Making progress.  Close weather is helping out Brrrr!

I am having a hard time getting photos to embed in the replies. I seem about 5 options for inserting photos but cannot figure out how to make any of them work. What is the secret to putting a photo in a post (just like every other forum)?

Trying to upload photos again.

roddie wrote:

MauricioB wrote:

Hi Roddie, it's very interesting all the comment you make. I am very surprised by the large number of variables that make a Cox engine work well, regular or poorly, or do not work directly. I think Cox, I reach almost every corner of the world, what happens is that many people left because of lack of knowledge for the proper functioning of them.
Today that I have taken up the theme of the Cox engines, I am overwhelmed by the number of variables that can happen in a single engine so that the result is very good or disastrous.
I fully agree with you that the valve assembly and retention ring are a vital point in all engines that have this system, as even the Pee Wee .020, the latter is much more critical - delicate - even though the line Of the 0.049.
I remain attentive to such good information! Regards....

Hi Mauricio, Yes.. it is interesting to learn about more ways to get consistent or "better" performance from the Cox engines. I found that installing "larger" fuel line for an external tank, helped to get fuel to draw through the line using a "Killer-Bee" (large venturi) backplate on a suction-only feed. This might help the Tee Dee to draw fuel better too.

I made "compression-fittings" to squeeze the ends of the fuel-line smaller.. for a tight-fit on the smaller NVA nipple/tank fittings.




Smaller line was developing "air-bubbles" when the engine ran-off the exhaust-prime. This cured that issue.

Roddie,That good information !, true, air bubbles !, so when more diameter tend to disappear !, good data !.
You know that in my experience I've noticed ....: the engine with its own vibrations at high rpm, makes the valve flapper move and automatically vary the setting and engine turns ..... God !, Pee Wee 0.020 if He is easy friend!

I think I should have a flight worthy plane today. I did notice that using a BW motor seems to leave me tail heavy. I am not sure if the steel pushrods are a bit too heavy. I will try balancing with them out to see if that gets me in the neighborhood.

Eric, did you ever sell that throttled 09?

Yes Scot the Throttled .09 Medallion is on its way to a good home , i looked for the how to insert Pics tutor but couldn't find it was hopping you had figured it out . If you click on the pic icon and then select files , after they are finished loading to bar press the Insert button that should do it . You not have any lead weight to put into the model to balance? I will have some .09 s for sale pretty sone though TD or Med. Did you enjoy that Heat wave yesterday at 73* for one day after being 5* this past weekend, Hope you can get it in the air .