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testors with modified glow head

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testors with modified glow head

Post  ninjaman on Sun Jul 10, 2016 8:53 am

Hello,
I bought a Testors Spitfire off ebay, https://www.youtube.com/watch?v=gV0iHibkR6A, I took apart the engine and the glow head filament was broken. I thought that I would try modifying it to take a regular glow head. I bought the 1/4 32 tap and tapped the hole and the plug fitted fine. There was a big gap between the top of the inside of the glow head and the plug. There was about four/five threads between the filament and the top of the compression chamber (if you get what I mean).
I decided to cut down the top fine to lower the plug, now the plug sits a little proud of the compression chamber top. When I turn the prop it feels like it is getting stuck before TDC, I can push it through that position but with more force than usually required. I think that I have increased the compression ratio a little too much (if my knowledge of engines is correct). When I tried to start the engine it did go for a few seconds. I think that I will have to put in a washer to create some space in the compression chamber.
Is there an ideal starting position for the needle valve? getting this thing going is a little tricky and frustrating.

Thanks
Simon
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Re: testors with modified glow head

Post  batjac on Sun Jul 10, 2016 7:40 pm

Simon, I assume you're using the original aluminum head gasket that came with the Testors engine. I measured the Testors head gasket, which is very thick, with a pair of digital calipers. I found that 5 Cox .049 head gaskets equals one Testors aluminum gasket.

As for the needle starting position, I found that 5 turns open start my pipe bombs and after break in the engines peak around 3 3/4 to 4 turns open.

The Measurin' Mark
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Re: testors with modified glow head

Post  ninjaman on Tue Jul 12, 2016 12:33 pm

Still cant get this thing to fire. I don't know what I am doing wrong. I was thinking about stripping it down and showing (in a video) the insides with some description. With the compression really tight as it is compared to my other engines, it does seem to fire once. It makes a loud popping sound but only the once.
Not sure what to do really, I want to get it flying but cant seem to get it to work.
Any advice would be great!
Thanks
Simon
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Re: testors with modified glow head

Post  pkrankow on Tue Jul 12, 2016 1:37 pm

Has the engine been apart? Recently? Are there burrs on the exhaust ports from tools? This can be fixed, carefully, with rubbing compound.

If you apply a bubble agent to the outside of the head are there bubbles anywhere? (I simply use fuel when I am at the field, not a good agent but good enough. No clean up too, unlike soap/water mixes or Windex)

What plug are you running? Is it a good plug? What temperature? (should be in the medium/hot to hot range for a 1/2a engine, typically)

If the glow plug is too long, try a "short" plug. Is there a plug gasket? Doubling up on plug gaskets has been done in the past when a short is required and not available, but it is not recommended. Any mark between the two gaskets can cause a leak just like a crease in a head gasket can cause a leak. Lapping the plug gaskets on some very fine sandpaper (400 or finer with oil) can help if you are forced this way.

Are there enough head gaskets? This was mentioned earlier by Batjac who is more knowledgeable about Testors engines.

Are there any leaks in the bottom end of the engine? The reed? The engine back to case? Have you done a suck/blow test with the reed and a clean piece of fuel line?

When you say "one pop" are you meaning running on prime, say a second or less, or a literal single pop?

How are you priming? Typically 1/2a engines, and even some bigger ones, having the exhaust closed and hanging a drop on teh side of the piston is all the required fuel. Blowing fuel into the cylinder is typically enough to flood the engine.


Phil
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Re: testors with modified glow head

Post  ninjaman on Tue Jul 12, 2016 4:29 pm

I think I may be flooding the engine, not to sure how much to use. I will keep that in mind when priming. The pop comes from the prime like you say, an initial burst of life and then dead.
I have not done any of those things that you mentioned, like blowing the reed valve. I am guessing that the exhaust port is the back of the engine opening. Where you see the piston there is a front opening and a back opening, I am guessing you mean the back when you mention the exhaust.
I have two gaskets between the plug and cylinder head. There is one gasket between the cylinder and cylinder head. I don't have any more, what is a good substitute?
I will try to research those other things. I don't think there is a leak. I have noticed a leak in the past coming from the cylinder head, I just tightened the cylinder head.
Thanks for the advice, I will report what happens
Simon
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Re: testors with modified glow head

Post  Oldenginerod on Tue Jul 12, 2016 5:14 pm

Both front & back are exhaust ports, so a prime at either is fine. Also, it may be a good idea to place one drop in the air intake. That is the small round hole right beside the needle valve. I'm not sure if you can get to that with the engine in the plane. If the reed is stuck, a drop of fuel here may help to unstick it. If the engine runs a bit longer with a drop in the intake, then the problem is most likely a blocked fuel spray bar. Remove the needle valve & blow into the hole it came out of with a small piece of tubing.
If the engine still feels tight at TDC, try to establish if it is mechanical interference or simply excess compression. I don't think you will give one of these engines too much compression.

Rod
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Re: testors with modified glow head

Post  pkrankow on Tue Jul 12, 2016 5:38 pm

The intake has the reed. My best guess is this is a reed problem causing a fuel feed problem, or a plugged NVA

I would remove the needle and forcibly flush the needle assembly. This will flood the engine. It also may float out trash from the reed seat too. Clear the flood first by tipping up the engine and draining it, then trying to start it till it barks. Then fuel it, set the NVA (3-5 turns from closed?) prime the exhaust only (since it already should have some fuel in the case) and have at it.

(note: I use this method on Cox reed engines that I have reason to suspect they ingested some dust or dirt and/or every 5-10 flights or so)

If it doesn't cooperate then a partial tear down is in order to verify and clean the reed, reed seat, and make sure the back of the engine is in good order with nothing pinched. The suck/blow test with some clean fuel line is used to verify the operation of the reed.

Phil

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Re: testors with modified glow head

Post  ninjaman on Mon Aug 01, 2016 7:35 pm

Hello,
I have stripped down the engine and forced fuel throw the valve which seems clear. I have removed and cleaned the reed. I then tried the engine. I can usually get it to pop along for a second or two, I have tried a fresh battery as I can not always hear the sizzle. I put a little amount of fuel on the intake and start flipping the prop. I can feel the prop tighten, then feel a kick. It is about half a turn on the prop to get this kick but it doesn't always happen. When it does fire, it runs erratically. I can not get it to run for more than two to three seconds tops. I tried a larger prop but that has no effect. I will try again tomorrow.
Any advice would be greatly appreciated.
Thanks
Simon
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Re: testors with modified glow head

Post  Oldenginerod on Mon Aug 01, 2016 10:53 pm

Feeling a "kick" as you turn it over slowly usually says that it's a little flooded. Sounds like it's over-compressed. I think I mentioned about the different heads/gaskets in an earlier post. This engine should have a really thick alloy head gasket. Your description of the erratic running make me think it might be bouncing backwards and forwards on the compression, and not actually turning over. Are you using the spring starter? Maybe it needs a little more authority in the flick. If you're not accustomed to flicking props it can be a little daunting at first, but don't be scared to get in and give it a really good strong flick.
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Re: testors with modified glow head

Post  pkrankow on Tue Aug 02, 2016 6:47 am

If it is going back and forth instead of full revolutions there is no doubt that it is over compressed. A reed engine will run like that for a surprisingly long time sometimes. The best way to tell is to have a high contrast between the visual background and the prop, viewing the prop from the front or rear of the engine. You need to know where Top Dead Center is as that is the part that will not have a prop sweep visible.

Phil
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Re: testors with modified glow head

Post  gcb on Wed Aug 03, 2016 8:11 am

Simon,

First, remove the plug and make sure the engine turns over smoothly.

Second, replace the plug and turn it over and check that it still turns over smoothly. Don't confuse high compression with hitting the plug with the top of the piston. If in doubt, use a shorter plug or add extra plug gaskets. The plug should not protrude into the combustion chamber far enough to hit the piston.

Third, close the needle all the way and practice starting off a prime. Correct any problems that prevent an easy start-up. Once you can do this, then try it with the needle open. I would suggest opening a couple of turns at a time. That will prevent flooding on start-up.

George
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