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TT .39 heli engine ruens glow plugs

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Old 09-01-2012, 07:47 PM
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Basil Yousif
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Default TT .39 heli engine ruens glow plugs

I have the Thunder Tiger .39 heli glow engine on a Raptor 30. The engine is starting to ruin glow plugs only after one flight. It also has a problem sucking in fuel while trying to start it.
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Old 09-01-2012, 09:06 PM
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Default RE: TT .39 heli engine ruens glow plugs

rear bearing is going bad.
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Old 09-01-2012, 09:32 PM
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Default RE: TT .39 heli engine ruens glow plugs

If you are having fuel delivery issues it is probably going lean and burning up the plugs. Check for things like cracked fuel nipples, ho;es in fuel lines , carbueretor gaskets leaking, loose fuel fittings etc.
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Old 09-02-2012, 04:15 AM
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Default RE: TT .39 heli engine ruens glow plugs

Rear bearing
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Old 09-02-2012, 04:57 AM
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Default RE: TT .39 heli engine ruens glow plugs

One thing to do is to examine the glow plug element closely. You can use a jeweler's loupe or something else to get a good view of it. The glow plug element's condition can be very helpful in determining why you are ruining glow plugs.

Here is a good article on what to look for with a glow plug.


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Old 09-02-2012, 08:03 AM
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Default RE: TT .39 heli engine ruens glow plugs

Did you by any chance use RTV to seal the muffler?
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Old 09-03-2012, 06:39 AM
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Default RE: TT .39 heli engine ruens glow plugs

I've used RTV to seal backplates, carbs, and mufflers for years. Never a problem with glow plugs. I am going to agree with previous responses; bearings or fuel delivery problem.

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Old 09-03-2012, 04:59 PM
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Default RE: TT .39 heli engine ruens glow plugs

Before you run the engine again, take off the back plate and inspect the rear bearing. The bearing cage may be breaking apart. If so then a big chunk of it may breaks off and damage your piston and liner. That is what killed my Pro 46. I had several glow plugs go bad and I didn't realize what was happening until it was too late.
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Old 09-03-2012, 06:30 PM
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Default RE: TT .39 heli engine ruens glow plugs


ORIGINAL: earlwb

One thing to do is to examine the glow plug element closely. You can use a jeweler's loupe or something else to get a good view of it. The glow plug element's condition can be very helpful in determining why you are ruining glow plugs.

Here is a good article on what to look for with a glow plug.



I had a scrapbook of "Duke's Mixture" articles that got lost in a cross-country move of my household. I'd sure like to find some or all of them. Do you have a source?

TIA,

CR
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Old 09-04-2012, 09:21 AM
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Default RE: TT .39 heli engine ruens glow plugs

The rear bearing is probably shot that sounds like it I'll check it. The glow plug looks like it's had someone stick a nail inside where the filament is. It's pushed in. I always use RTV in the muffler.
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Old 09-04-2012, 09:39 AM
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Default RE: TT .39 heli engine ruens glow plugs

RTV to seal mufflers is a recipe for disaster. First, you don't need it. Second, if you use anything more than the very thinnest smear, it can/will fleck off and get sucked into the combustion chabmer during the intake portion of the stroke. If that happens it will snuff the glow plug immedately.

A properly faced muffler/engine joint doesn't need any gasket or RTV. If the surfaces aren't flat, then a thin smear of 5min epoxy will seal it without the issues of RTV
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Old 09-04-2012, 10:23 AM
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Default RE: TT .39 heli engine ruens glow plugs


ORIGINAL: Charley
I had a scrapbook of "Duke's Mixture" articles that got lost in a cross-country move of my household. I'd sure like to find some or all of them. Do you have a source?
TIA,
CR
Sorry no, just a few I gleaned from other sources here or there.


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Old 09-05-2012, 04:39 AM
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Default RE: TT .39 heli engine ruens glow plugs


ORIGINAL: BarracudaHockey

RTV to seal mufflers is a recipe for disaster. First, you don't need it. Second, if you use anything more than the very thinnest smear, it can/will fleck off and get sucked into the combustion chabmer during the intake portion of the stroke. If that happens it will snuff the glow plug immedately.

A properly faced muffler/engine joint doesn't need any gasket or RTV. If the surfaces aren't flat, then a thin smear of 5min epoxy will seal it without the issues of RTV
I dont see the argument that RTV kills glow plugs to hold water, at least with my experiences. I've never had a glow plug get snuffed out because I used RTV to seal any part of the engine. Every engine I own has a leaky muffler without any sealant on it. Whether it leaks from where the two halves meet, the end caps, or the flange at the exhaust port.... they all weep a little bit. I'm lucky I haven't lost a muffler or part of one. Since I used some black or orange RTV to seal the muffler, they don't come loose and leak anymore.

No offense, but epoxy would be the LAST thing (remember, this is my opinion) I would ever use to "fix" a leaky mating surface. What would happen if a little fleck of that epoxy got into your engine...? That would be more damaging to the glow plug than a little silicone rubber IMO.

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Old 09-05-2012, 05:08 AM
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Default RE: TT .39 heli engine ruens glow plugs

To each his own, I'm only passing on my somewhat limited experience
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Old 09-05-2012, 05:17 AM
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Default RE: TT .39 heli engine ruens glow plugs


ORIGINAL: BarracudaHockey

To each his own, I'm only passing on my somewhat limited experience
I wasn't trying to beat you up, just so you know. I just havent had it happen to me in 15 years of modelling. [&:]
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Old 09-05-2012, 07:29 AM
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Default RE: TT .39 heli engine ruens glow plugs

Hi!
Could be that you set it too lean!
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Old 09-05-2012, 08:10 AM
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Default RE: TT .39 heli engine ruens glow plugs

ORIGINAL: Basil Yousif
I have the Thunder Tiger .39 heli glow engine on a Raptor 30. The engine is starting to ruin glow plugs only after one flight. It also has a problem sucking in fuel while trying to start it.
Going back to the first post again. A problem sucking fuel implies a air leak somewhere. The O-ring under the carb is the first thing to check. You must push down on the carb hard to compress the O-ring a little before tightening up the screws or clamp. The next is the back plate might be loose. The head could be coming loose too. Then we get to the bearings, where the front bearing may not be sealing like it should leading to an airleak too. Then there is adjusting the engine to run too lean, heli engines tend to run a little more on the rich side than airplane engines do.

Of course we do not know what fuel the OP is using. Too much nitromethane can be a problem if the engine isn't set up for it.

Also what brand glow plug is the OP using. The wrong heat range plug can be a problem. Years ago I got a batch of defective major band name plugs too. I went through one flight per plug, I never bought any of those brand plugs since then.


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Old 09-05-2012, 11:30 AM
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Default RE: TT .39 heli engine ruens glow plugs


ORIGINAL: earlwb

ORIGINAL: Basil Yousif
I have the Thunder Tiger .39 heli glow engine on a Raptor 30. The engine is starting to ruin glow plugs only after one flight. It also has a problem sucking in fuel while trying to start it.
Going back to the first post again. A problem sucking fuel implies a air leak somewhere. The O-ring under the carb is the first thing to check. You must push down on the carb hard to compress the O-ring a little before tightening up the screws or clamp. The next is the back plate might be loose. The head could be coming loose too. Then we get to the bearings, where the front bearing may not be sealing like it should leading to an airleak too. Then there is adjusting the engine to run too lean, heli engines tend to run a little more on the rich side than airplane engines do.

Of course we do not know what fuel the OP is using. Too much nitromethane can be a problem if the engine isn't set up for it.

Also what brand glow plug is the OP using. The wrong heat range plug can be a problem. Years ago I got a batch of defective major band name plugs too. I went through one flight per plug, I never bought any of those brand plugs since then.


earl the problem with sucking in fuel is a air leak but not where your thinking lol. the bearing is shot. parts of it have tore up the piston to sleeve fit. the wear from this has bits of aluminum going to the plug and causing to burn out.

NEW ENGINE!
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Old 09-05-2012, 01:09 PM
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Default RE: TT .39 heli engine ruens glow plugs

Ok, I think that  you are likely correct about that.

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Old 09-05-2012, 04:13 PM
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Default RE: TT .39 heli engine ruens glow plugs

Basil have you removed the engine from the heli yet and inspected it?
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Old 09-07-2012, 11:15 AM
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Default RE: TT .39 heli engine ruens glow plugs

I took the engine apart but I couldn't find andything wrong. Check the pictures out and see if there's anything that sticks out. The shaft and piston movments are smooth and have no play in fact pretty good for an engine that has ran for 4 years.
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Old 09-07-2012, 01:53 PM
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Default RE: TT .39 heli engine ruens glow plugs

Now is a good time to replace the bearings. They are likely the culprit in this case.

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Old 09-07-2012, 04:56 PM
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Default RE: TT .39 heli engine ruens glow plugs

yes bearings and a new ring. Kinda hard to tell but looks like the chamber is nicked up from bits metal. get better picks on the head.
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Old 09-08-2012, 10:15 AM
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Default RE: TT .39 heli engine ruens glow plugs

So the bearings can still be bad even if they look good, I guess just a little bit of wear and the vibration can ruin the plug. The shaft does move with no play.
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Old 09-08-2012, 12:22 PM
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Default RE: TT .39 heli engine ruens glow plugs

If the engine is apart its best to do the bearings. The only way to truly examine them is to remove them from the engine, put a side load on the bearing and turn it with your finger to see if its notchy, but for the price of a set from RC Bearings.com if you're going to do that you might as well throw them out and replace them.

Vibration won't make your plug go bad.

Running too lean, using RTV for a muffler gasket, and a bearing coming apart will make your plug go bad.

As for the RTV, if you use a very thin smear where none oozes out into the exhaust flange, you're fine, most people tend to over do it and it WILL snuff your plug immediately if if flecks off and gets back into the combustion chamber, this is well documented.
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