190 "Kinda Special"

You have got a very nice finish on the plastic - did you use anything to "finish" it. I always end up with a very rough finish on plastic.

Looks good! You can push the spray bar out and drill the venturi out for more rpms. If you don't go to crazy it will still draw fuel on suction if your not doing loops. That's a fine thread needle on those so if you want to run a bladder you can really drill that sucker out and gain about 1000rpm.

Jim

Thanks Guys!

Ian, I used an ordinary rather coarse file to remove the majority of the material and then a finer one to smooth out the surface. The fine file is labeled "mill file, bastard cut". I just moved the file in a light, steady slow stroke, and at the same time just a little sideways. One direction only, not back and forth. This brought out "fresh" Delrin, so the filed areas do look pretty good.

The inside of the intake was finished with a Scotch Brite type of product after the initial grinding. It left a flat surface, and also all the surfaces of the backplate that were left intact were a little faded. I just wiped the whole thing with air tool oil, it restored the look but of course it is now "oily", so it's not perfect.

EDIT 1: in the picture where I hold the part in my hand there is no oil or anything on it, so that's what it looked like before any treatments. After that it went into the ultrasonic with warm water and hand dish detergent and then the oil.

EDIT 2: Jim, if I push out the nva, how should I re-attach it? I thought they were sort of forced into position at the factory and not meant to be removed?

Thanks. I have tried all sorts of products for restoring delrin with no success. Any that have looked promising haven't been permanent.

KariFS wrote: Jim, if I push out the nva, how should I re-attach it? I thought they were sort of forced into position at the factory and not meant to be removed?

They're not, Ha! But, if you use the back end of a screwdriver handle, a dowel, or something similar and push on the needle end of the spray bar  (with the needle removed) it will come out. Force it back in needle end first. The trick is to not do it too many times or the fit gets sloppy and the spray bar will turn with the needle.

Jim

Jim, when you use a bladder with the fine needle plastic backplate, how many turns open do you start at?

The Student Mark

JPvelo wrote:.... push on the nipple end it will come out. Force it back in nipple end first. Jim

I can't say for sure, but I was pretty certain that the spray bar needs to come out the other way, pushing out from the needle side????

Oldenginerod wrote:

JPvelo wrote:.... push on the nipple end it will come out. Force it back in nipple end first.  Jim

I can't say for sure, but I was pretty certain that the spray bar needs to come out the other way, pushing out from the needle side????

You are correct! Sorry, it's been a few years since I've done one. I'll go back in and edit my previous post.

The embarrassed Jim.

batjac wrote:Jim, when you use a bladder with the fine needle plastic backplate, how many turns open do you start at?

The Student Mark

Mark,

Here's a write up I did when I first started doing these, all the info is in there.

https://www.coxengineforum.com/t3536-cranking-up-a-reed-valve-cox-on-bladder-pressure?highlight=Bladder

Is that a DIY aluminum bullet spinner?

While this may not be on topic with the subject, Mark raised the question of how many turns should the needle be out. That question is impossible to answer . This is due to many factors especially the taper of the needle. There was at least 3 style of 128 TPI needles that I own from Cox where there's a step in it. So to answer the question directly, with the bladder feed tubing pinched closed, holding this particular engine level, open the pinch off and wait a sec for the fuel to come dripping out. Adjust the needle until the drips are about 3/4"-1" apart. If the fuel is streaming out, it's obviously open too much  and if you can't control the drip as I mentioned it's not going to work and their could be a problem with a clog in the spraybar or a fault in the needle. If the needle is set too lean, the engine may run, but it will surge up and down in rpm and the needle will have to be immediately opened.

         Once the drip is set, starting procedures are pretty much the same. I like to run a prime through 2 times prior to opening the pinch off. I like to clear the engine and get a bit of heat into it prior to running on the bladder. Don't adjust your needle too quickly once it's running unless the setting is too lean. Trying to adjust the needle on a cold engine is going to result in a not so favorable needle setting. Stay on the ground a few seconds, I like to hold my finger on the head until I can't hold it there to get the to end heated up and the setting can now be adjust without a major change due to temperature.

For those interested in trying bladder pressure, I highly recommend using a additional head gaskets to give your plug life a bit more duration. If you don't feel the need for them, you can always remove them.


Running bladder pressure doesn't always allow for the same size prop one would run on suction, the needle sensitivity becomes too great. To counteract this, run a smaller prop and use higher nitro. This will allow for a fine adjustment and reliability. Your launch rpm is dictated by your needle setting. Quickly pinching the fuel line from the bladder should cause the engine to rise in rpm's quickly. If you pinch the line and it wants to quit, your settting is too lean. The engine is going to unload in the air and you must counteract this by launching slightly rich. The higher the nitro, the richer the setting during launch. Another tell tale sign is the end of the flight. WHen the head pressure of the bladder depletes, the engine run goes richer at the end of the flight. If your setting was  on the rich side, the very last few laps of the flight will yield a lean run. This means you can go in a bit more on your needle during launch.

1/2A Nut wrote:Is that a DIY aluminum bullet spinner?

I wish It's just a silver color Cox rubber spinner. I have two of them, not sure which model they are from.

KariFS wrote:

1/2A Nut wrote:Is that a DIY aluminum bullet spinner?

I wish It's just a silver color Cox rubber spinner. I have two of them, not sure which model they are from.

The silver rubber spinner came from the first version (c.'68) of the Corsair and used a couple years, when it was revamped, bellcrank moved into fuselage and red spinner added.

Thanks Mark, it's nice to know where at least one of my p.s. engines came from

EDIT: BTW, is that a left hand prop?

KariFS wrote:Thanks Mark, it's nice to know where at least one of my p.s. engines came from

EDIT: BTW, is that a left hand prop?

I have a couple of Cox L/H 3-blade props like that. Mine are 5d x 3.5p black, square-tipped/solid-hub. Might be a good prop to try. Bernie (Cox International) currently has them in stock. I've had mine for YEARS.. not sure where they came from. Bernie's are listed as "pushers".. but on a reedie you could just run them L/H "tractor" and gain some line-tension. It would be interesting to note the difference +.5" of pitch makes. Not quite the load of a 5 x 4... but a little more edge than a 5 x 3.

I think a 5x3.5 three blade would have about the same load as 5x4 two blade, I do think you loose some efficiency with a three blade. The square tip LH prop was designed for the Corsair, with the thought of increasing line tension, possibly from input from Dale Kirn, who worked at Cox at the time. I think Bernie's is the same just mislabeled.

The complete article has now appeared on Outerzone:

http://www.outerzone.co.uk/planfile_supplement/6104/290_Special_oz6104_article.pdf

Oops, that link didn't work, let's try another one:

http://www.outerzone.co.uk/download_this_plan.asp?ID=6104

KariFS wrote:The complete article has now appeared on Outerzone:

http://www.outerzone.co.uk/planfile_supplement/6104/290_Special_oz6104_article.pdf

Oops, that link didn't work, let's try another one:

http://www.outerzone.co.uk/download_this_plan.asp?ID=6104

I couldn't access either of these Kari.. I'll be following this thread.. because the whole concept of re-using this little product engine in a more capable balsawood model, I find endearing!

Did you bench-run the engine yet? The backplate came out real nice!

I have to wonder about the connecting-rod that was in there when you took it apart.. That's not something that you see everyday.. and probably wasn't done by a novice. How did the crank-pin look? I assume you're using that same crank? When you replace the backplate screws (assuming you haven't yet..) it would provide the opportunity to observe if there's any "slop" in the fit of the crankpin with the replacement piston/rod by rotating the prop-driver back and forth. If there is.. I would personally replace the crank.. or crankcase assy.

On the other hand...  Did the "old" piston/rod look ok (otherwise) when you removed it from the cylinder? You might want to hang onto that piston/rod. I don't consider myself an engine-guru by any stretch of the imagination.. but by the looks of it; someone went to a lot of trouble to thin-out the pin-end of that connecting-rod. You could measure it's "web".. but I'm guessing that there might be as much as a 50% reduction in bearing-surface (friction) area.. as well as more "end-play" on the crankpin. Having a ball-socket joint design "up top".. this might equate to a hotrod engine-mod    You just never know. I'm not implying that this mod would be suitable for longevity.. but could have been done as a maximum-performance effort to gain more rpm's. You did state the glow-head was burnt-out. This "might" have been caused from high-rpm operation. Only the person who massaged that connecting-rod could give you that answer. Do you have their contact info?

Roddie, if the link still doesn't work, you can find the article by going to outerzone.com, then searching "290". On the 290 Special page click "downloads" button, that should get you to the page where you can either click and open the plan or the article. The article is in PDF format, I don't know how to post those or if it is possible at all. I suppose I could try to capture the pages as "images" and then post them, but I'm running a little short on round-toits...

It never occurred to me that the rod mod would be a performance thing, I figured it was maybe caused by abuse by starter or pusher prop use in another engine, or maybe a "fixed" big end meltdown or even a left-over from an attempt to make a twin engine.

The crankshaft and the crankcase both looked intact, I polished them and did not see anything out of the ordinary. This engine was thrown in to the pile when I bought 4 or 5 other engines. The other engines were "almost-NIB" except for this one and a dirty TeeDee .051. Now that I think about it, the TeeDee did have 4 or 5 head shims and a piece of fuel hose around the needle valve, so it could be that a previous owner is/was after performance

The guy I bought the lot from had got the boxed engines from "an older fellow who liked to build planes but lately had not been flying them a lot", and due to the past tense I didn't ask anything further about him, not even sure if he's still around.

I did (of course) keep the modified piston/rod, thought about using it as a part of a honing tool or something. But I will now investigate the "hot rod" aspect also

I haven't run it yet, I'll need to get the brackets done first. I did find the necessary aluminum material for the brackets and bought the balsa for the plane though. My drill press is still under a pile of junk in some corner of the garage, but I already found the vise a few weeks ago Moving in a hurry is hell, 3 years after my workshop is still a mess. I've been too busy looking for my tools to organize the shop I guess