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Why the whistle?

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Why the whistle?

Post  Oldenginerod on Tue Jan 13, 2015 12:37 am

Looking for some clues here.  I have an .049 which I built up a couple of years ago out of parts I acquired in a couple of ebay parts lots.  Later parallel crankcase, Tee Dee #4 cylinder with standard head, plastic 8cc tank & plastic backplate.  When I first assembled it I fitted a Tee Dee head, along with all new gaskets and a new steel reed.  First run was mindblowing!  Thumbs Up  It screamed so hard that it scared me, but after the initial run, I couldn't get it to start, not even pop.  Thumbs Down  Head was fine, but it now felt like it had very poor comprssion.  I dismantled it & checked the piston & bore and there's no obvious damage or wear.

Fast forward to now.  I mounted it up the other day just to see if I could get it to run, which I did, but it required an electric starter.  Performance was mediocre but it did run.  I noticed while starting it that it had a high pitched squawk on every rotation, almost like a dry bearing noise, but everything is nice & free.

Today I removed the tank to check the reed.  Firstly, the plastic reed retainer was stuck in the back of the crankcase.  I refitted it to the tank and could barely suck through it.  I fitted an old star shaped mylar reed and it was easier to suck through, but was just like a sports whistle.  I put it back together and the squawk is even more pronounced.  I've never heard a reed make so much noise.  I haven't tried to start it since swapping the reed.  I haven't really had any experience with the plastic type retainers so I wonder if I've missed something.  Huh...

Rod.
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Re: Why the whistle?

Post  TDbandit on Tue Jan 13, 2015 1:00 am

I have a product engine doing the same thing, it runs fine but it has an annoying chirp to it all I can think of is the reed not sealing properly or the new style retainer is allowing the reed to float off its seat too far "shrugs". As far as compression goes this is a long shot but I once had a piston wear through the crown in the center where the ball/socket is, it was about the size of the tip of a fine ball point pen but it was enough to cause compression loss. This happened to a babe bee I had that I ran the dang bejesus out of. the cylinder/piston fit was fine. it was just the little pin hole on top of the piston took me forever to find it. You could of maybe gotten a piston that had a few resets on it and wore through on that screamer of a run you had. (Bandit)
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Re: Why the whistle?

Post  balogh on Tue Jan 13, 2015 2:50 am

Had the same experience with the piston crown punctured by the ball, when the fit was set too tight - though the ball oved easily in the socket, but the gap was just too small - and the formerly established varnish was abrased off the socket and could not reinstate itself due to the tight fit.

Although the resetting tool manual states the desired mimimum gap to be left when setting the balljoint, it is - at least for me -impossible to measure...I have developed since my early mishaps a natural feel of what gap may be right and stop hammering it just in time.
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Re: Why the whistle?

Post  TDbandit on Tue Jan 13, 2015 9:43 am

balogh wrote:Had the same experience with the piston crown punctured by the ball, when the fit was set too tight - though the ball oved easily in the socket, but the gap was just too small - and the formerly established varnish was abrased off the socket  and could not reinstate itself due to the tight fit.

Although the resetting tool manual states the desired mimimum gap to be left when setting the balljoint, it is - at least for me -impossible to measure...I have developed since my early mishaps a natural feel of what gap may be right and stop hammering it just in time.
I do the same thing. As you said, there is no easy way to measure the ball gap. I have done it once by taking a piece of wood, drilled a hole  that was just small enough to have a fairly tight fit around the rod and shallow enough where it would not touch the bottom of the piston skirt then clean the piston of all oil "you want the socket dry" then insert the rod in the hole till it bottoms then take a dial indicator fixture and set it up where it just touches the top of the piston and zero out the indicator then measure the deflection as you lightly tug up and down on the piston and take a note of the readng. It;s not easy so I just now go by feel "tap, tug, rotate and tap again" until i get the feel i like. The sad thing is you can only reset a piston so many times before it punches the top of the piston. (Bandit)


Last edited by TDbandit on Tue Jan 13, 2015 9:52 am; edited 1 time in total
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Re: Why the whistle?

Post  balogh on Tue Jan 13, 2015 9:48 am

my experience is that the socket and probably the ball as well are hardened as your engine runs more and more, and after an initial 1-2 resets on a young piston you do not have to bother with another reset.

My veteran 051 has run way more than 100 hours so far and I have not had to reset it in the last 80 or so hours.
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Re: Why the whistle?

Post  TDbandit on Tue Jan 13, 2015 10:01 am

balogh wrote:my experience is that the socket and probably the ball as well are hardened as your engine runs more and more, and after an initial 1-2 resets on a young piston you do not have to bother with another reset.

My veteran 051 has run way more than 100 hours so far and I have not had to reset it in the last 80 or so hours.
Yeah you're right it work hardens forgot about that. Either way that's how I've measured it in the past not easy though. (Bandit)
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Re: Why the whistle?

Post  GWILLIEFOX on Tue Jan 13, 2015 10:13 am

What is the clearance supposed to be? How many thousands?
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Re: Why the whistle?

Post  TDbandit on Tue Jan 13, 2015 10:17 am

GWILLIEFOX wrote:What is the clearance supposed to be?  How many thousands?
End play is from .001 to .003 very tiny. (Bandit)
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Re: Why the whistle?

Post  roddie on Tue Jan 13, 2015 10:40 am

Hey Rod, Just a "guess" here.. You mentioned an electric starter. A photo of your engine would help.. but you say that it has a plastic "integral-style" 8cc tank.. (like a Black Widow?) and has a plastic reed-retainer.. (like the newer-style horseshoe back-plate?) I was thinking that the pressure against the reed-retainer from the crank-pin; using an electric starter could have worn and/or possibly distorted the retainer from the friction/heat. If the front of the case is worn (also a symptom of using an electric starter).. this could definitely have happened.. and would explain why the retainer was stuck in the case.

I would disassemble the engine again.. and try replacing the reed-retainer (if you have an extra one) and install a starter-spring.

If you're in the habit of using an electric starter.. keep an oil can with your engine-running accessories.. and place a few drops behind the prop drive-plate; working it in by hand-flipping a few times. I go "easy" on the pressure when using my electric starter.. and use quick bursts. I also have the starter running before I completely engage the spinner. I think it's a little safer.. and could save from breaking the con-rod if the engine is flooded.
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Re: Why the whistle?

Post  pkrankow on Tue Jan 13, 2015 1:10 pm

If compression seems low or non-existant I would chase head gaskets.

Many of my reed engines whistle or chirp while starting or priming. If it doesn't become a pop (pop) pop sound (reed open, compression over TDC , reed close) when I cycle the engine _s_l_o_w_l_y_ I flush the reed out by pulling the needle and backflushing through the needle threads (pinch the fuel line if you can). This naturally floods the engine to an insane level BUT it will often float out trash and allow the reed to seat properly again without a tear down. Hold the engine sideways, or prop down, and slowly cycle it through. If the cylinder fills with fuel, or feels like it might have, do not pull it through compression, but go the other direction a couple flips.

On my basher, which gets driven into the dirt regularly, I have to back flush every 4-5 crashes, which when a handful of newbies are trying, is about every 15 minutes or so. Just memorize the needle setting and I often don't have to tweak with it after flushing and resetting. The setting is slightly different on different days. When an engine is hot and running right it should start on prime after only 1-3 flips. I flush when the flip count exceeds that.

Phil
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Re: Why the whistle?

Post  Oldenginerod on Tue Jan 13, 2015 3:01 pm

I'm pretty sure the reed itself is what's chirping. I've had it apart again and it's all nice and clean. The crank has no significant end float & hasn't been interfering with the retainer, which is not such a tight fit on the tank, but is tight in the case. I don't have another to try. I'll probably just pull the whole tank assembly off a good running engine & try that. If it solves all my problems I'll probably just grab a couple of new reed retainers next time I order.
As I mentioned, I only built the engine out of scraps. I was pretty happy to dicover the Tee Dee cylinder in amongst my parts lot & wanted to make use of it. I'm pretty sure I used a brand new piston/rod in it initially. I was just so disappointed in it after the initial high speed run, but I'll get it sorted out eventually.
Thanks for all your hints.

Rod.
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Re: Why the whistle?

Post  RknRusty on Tue Jan 13, 2015 3:13 pm

The only plastic 8cc tank I ever used eas on a Black Widow. It became misshapen and interfered with the reed. I threw it away and never tried another one. I agree that it's probably the reed chirping. I'd like to hear you post back and say it ran so fast it scared you again.
Rusty

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Re: Why the whistle?

Post  roddie on Tue Jan 13, 2015 7:52 pm

Rod, Cox International sells 3 different plastic reed retainers.. and each one is for a certain application. When looking at the 8cc plastic integral-style tank alone.. it states to use the "grey" plastic reed retainer (not the flanged type) Which one are you using? It's a bit confusing.. because they also sell an 8cc aluminum tank (conversion kit) that shows the flanged (black) reed-retainer being used. That would mean that they sell 3 different 8cc tanks; one requiring a "circlip" retainer, one requiring a flanged retainer.. and one requiring the round grey one having no flange. I'm still on the fence on whether the flanged one requires a gasket or not. I don't like the whole idea of either of the plastic retainers actually.

When Cox was still in business.. I ordered from them a few times. One such time; I got 4 of the old-style black horseshoe back-plates that use the circlip. Two of them now have broken/cracked clip-holders. I don't know what type of plastic it is.. but I don't think it's Delrin. I'm always nervous when changing a reed or cleaning.. that they'll break at the clip housing.

like this one..



Having these backplates got me designing/building my own airplanes though. Around that time, I had scored about two dozen Perfect wedge tanks; from tiny "midge" tanks.. up to 1.25oz. for around a buck apiece.



I went through a period in the early 90's where I built and flew a lot.. but then went through a long period of only sporadic building.. and virtually no flying.. up to the present. I'm glad that I managed to hang on to all my model stuff through the years.  Small Cox Logo
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Re: Why the whistle?

Post  Cribbs74 on Tue Jan 13, 2015 7:56 pm

It's the reed. It's always the reed.

The ball socket when really worn will make a clicking noise when turned over by hand. When running you can't hear the ball socket click.

The reed will make that noise when it is pinched and not free to rotate.



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Re: Why the whistle?

Post  RknRusty on Tue Jan 13, 2015 8:06 pm

Cribbs74 wrote:It's the reed. It's always the reed.

The ball socket when really worn will make a clicking noise when turned over by hand. When running you can't hear the ball socket click.

The reed will make that noise when it is pinched and not free to rotate.



Right. I usually only hear it when I perform the suck/blow test prior to assembly. Sounds like a baby duck call.
Rusty

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Re: Why the whistle?

Post  pkrankow on Tue Jan 13, 2015 10:32 pm

Cribbs74 wrote:It's the reed. It's always the reed.

The ball socket when really worn will make a clicking noise when turned over by hand. When running you can't hear the ball socket click.

The reed will make that noise when it is pinched and not free to rotate.



Ahhh. Thank you. I have not had a mini-duck-call experience yet.

Phil
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Re: Why the whistle?

Post  Oldenginerod on Wed Jan 14, 2015 1:48 am

RknRusty wrote:
I usually only hear it when I perform the suck/blow test prior to assembly. Sounds like a baby duck call.
Rusty
That's it Rusty!! That's what I'm hearing.  A baby duck call. lol!

Roddie.  It has the grey clip-on retainer.  It's the black plastic 8cc un-vented tank, so by your reckoning I have it right.  I think the outer rim of the retainer I'm using is clamping the reed hard against the outer circumference of the reed seat, so the reed has to flex in the middle to open the passage, rather then float away from the seat.
I'm sure somewhere I have an example of the black flanged type retainer, but I'm pretty sure all my aluminium tanks use a clip.
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Re: Why the whistle?

Post  pkrankow on Wed Jan 14, 2015 9:01 pm

Most aluminum tanks use a G clip. Some do not. There is an advantage to the plastic retainer. In case of a crank crash into the retainer the plastic takes the hit, the crank and tank are likely fine. With a G clip the tank takes the hit and probably has significant damage rendering it junk. The crank may also be damaged by the harder materials.

SOME reeds are out of tolerance and too long (it is rather rare for purchased reeds). Use super sharp scissors and shave a tiny bit off one end if you determine this is the case. Take the smallest amount the scissors will cut.

Phil
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Re: Why the whistle?

Post  roddie on Wed Jan 14, 2015 11:00 pm

I have reeds of Mylar, Teflon, Beryllium and Steel. The thicknesses vary as much as .010" (0.25mm)

For example;  
Beryllium-Copper (star-shaped)=.001" (0.025mm)
Steel=.002" (0.05mm)
Mylar=.005" (0.127mm)
Teflon=.010" (.25mm)

When you consider these differences.. you have to wonder about how the reed actually operates.. and ask yourself; does the retainer clearance between the seat, play much of a part in the reeds operation (no matter what the style of the retainer)? Naturally; the reed must be able to "flex".. and if a circlip/G-clip type retainer is too tight against the reed's outer diameter, it may hinder it's flexing.. preventing smooth operation.

The old Beryllium-Copper reeds were/are fragile at .001"... but that's the thickness that Cox originally designed them to work with the circlip style reed-holder. It would be interesting to measure the clearance between the circlip and the outer area of the seat without a reed installed, to see what it is. If it's less than .005".. then a Mylar reed (.005") is going to be pinched when the clip is installed. This could be checked with a precision shim/gage strip. I honestly can't see how a .010" thick Teflon reed would even function under a circlip.. but they do make them. I would guess that being able to achieve a .001" clearance would be optimal; so as not to either bind or excessively flutter.

Ron Cribbs is an advocate for having the reed free to rotate under a circlip.. and I can understand why. This is an area that I have definitely overlooked over the years.. and one that's probably caused inconsistent running between my reed-valve engines.
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