Destroying Glow Plugs

[Rick Sowell]

I need some advice on glow plugs: I have a .12 rigger that is going through plugs almost every run, the plugs are not burned out but are mangled and crushed, what causes this? this boat has a Picco 12 aircooled buggy engine, running 30% fuel, M440 prop, strut bottom even with the rear shoes bottoms, Macs pipe set at about 8 1/4", runs pretty well but I can hear it lose power in the corners with the extra load of turning, get off the rudder and it picks up alot of speed. I have tried to richen it up alot but can't seem to tell if that is what I should be doing. any thoughts from anyone?

 

[ACTION JACKSON]

I need some advice on glow plugs: I have a .12 rigger that is going through plugs almost every run, the plugs are not burned out but are mangled and crushed, what causes this? this boat has a Picco 12 aircooled buggy engine, running 30% fuel, M440 prop, strut bottom even with the rear shoes bottoms, Macs pipe set at about 8 1/4", runs pretty well but I can hear it lose power in the corners with the extra load of turning, get off the rudder and it picks up alot of speed. I have tried to richen it up alot but can't seem to tell if that is what I should be doing. any thoughts from anyone?

i would check your head clearance, example if your at 15 thou go to 12 thou

 

[jetpack]

Distorted glow plugs come from either too much compression for the percent of nitro being used, too much load on the engine, or too much scavenging from the pipe like a lean condition. Its telling you it is a "timing" problem.

Try lowering your compression, lengthening the pipe, or use a smaller prop and see what happens.

After you get your motor to hold a plug, this might be handy to look through also:

Reading Glow Plugs and Head Buttons

Before you try your next new glow plug, run it up to a hot red-orange and let it completely cool about five minutes, then run it up to hot again. Do this several times. It will heat temper your coil before it has to take the pounding of compresson and fuel. Do NOT go white hot with it...it will frost the coil, same as a lean run will do and cut down the action of the plug. You want the plug to stay glossy. Just stay red to orange and you should be okay. What is important is making sure the plug cools off as much as it did before heating it.

They naturally do this by themselves with each run, but you can give them a gentle head start on the process before they get pounded - and might not survive it. Like anything in a motor...glow plugs need breaking in also before they can take hard use. Always stay rich the first few runs with a new glow plug and give it a chance.

This used to be stated with every glow plug KB sold on the back of the package before the light went on that they shouldn't really be bragging how to lengthen the life of a plug. <_<

Remember also a glow plug should not really burn out that often. If treated in a modest tune, they should last past a couple jugs of fuel if not more. Some sport engines can go their whole life on it's original plug if it's kept in sport tune.

It is only when you step up to very high nitro (40%-60%) is when you start burning plugs every tank or so, because the coating on the coil is designed to react only with methanol...not nitromethane, and no setting will ever be correct for the plug to last any long length of time. Like they say, Nitro is pure dynomite...

 

[Chris Wood]

nobody has asked WHAT plugs you are running.

little motors like HOT plugs and if you are trying to run say a mc-9 it is way to cold. you could be leaning it out to much to compensate for a cold plug

let me know

chris

 

[jetpack]

Yep Chris is on the right track too.

Here is a couple of things that will help track and cure things also.

Repeated glow plug failure usually points to too much compression.

 

If the element is pushed up inside the glow plug after some run time to it, it means you need to lengthen your pipe setup or change to a warmer plug. If the element is gone, then the opposite is true and you should change to a colder plug or shorten up the pipe.

 

I would in either case, back off the compression. Always start with a soft engine, then after everything seems to be holding...a good mixture and plug stays shiney...up the nitro if you want, or start lowering your head clearance, or start bringing the pipe in until things start to fall off, then add back a shim or boost to a cooler plug, or load up a bigger prop.

 

Also a good idea to fully flush an engine when you blow a plug to remove any fragments. Sometimes those element fragments can imbed themselves into the piston or the head, causing a hot spot and cause pre-ignition and fool you, let alone tear up bearings or score the skirts especially if you blew it because of a lean condition.

 

Blowing glow plugs is never a good deal and should be taken care of right away before major damage happens because its more than just ash blowing out the exhaust, its shrapnel that can be trapped inside the engine, and not really the friendly kind because it can promote ignition all in the wrong spot or time. They are much different animals than spark plugs when they break. The element fragment can imbed itself into the skirt of the piston way down low, and still be glowing well enough to ignite the incomming charge waiting inside the crankcase. Although rare, can explain how sometimes crankcases split, or skirts blown out...not because of working strain, but because of a crankcase fire...backfire...

 

 

[Ron Olson]

Rick and I were talking in the chatroom last night and he's tried K&B's and an MC-9 with the same results. I threw a couple of suggestions to him but figured there are more people out here that know what the're typing about.

If you need head shims, I'll see what I have. I've got 2 parts engines.

 

[Don Ferrette]

A 40mm diameter prop sure sounds like a bit much for a .12....... :huh:

 

[Ron Olson]

Yup. Mine could swing a Prather 215 but not a 440 for some reason. Last night I also suggested a smaller prop.

 

[Don Ferrette]

Yup. Mine could swing a Prather 215 but not a 440 for some reason. Last night I also suggested a smaller prop.

Maybe try one of those Y535's that Bob C. is selling-

http://www.intlwaters.com/index.php?showtopic=31219

With a smaller 35mm diameter but higher 1.5 pitch progression it might go really well, then shorten the pipe and let it scream.

 

[Jack ODonnell]

Distorted glow plugs come from either too much compression for the percent of nitro being used, too much load on the engine, or too much scavenging from the pipe like a lean condition. Its telling you it is a "timing" problem.
Try lowering your compression, lengthening the pipe, or use a smaller prop and see what happens.

After you get your motor to hold a plug, this might be handy to look through also:

Reading Glow Plugs and Head Buttons

Before you try your next new glow plug, run it up to a hot red-orange and let it completely cool about five minutes, then run it up to hot again. Do this several times. It will heat temper your coil before it has to take the pounding of compresson and fuel. Do NOT go white hot with it...it will frost the coil, same as a lean run will do and cut down the action of the plug. You want the plug to stay glossy. Just stay red to orange and you should be okay. What is important is making sure the plug cools off as much as it did before heating it.

They naturally do this by themselves with each run, but you can give them a gentle head start on the process before they get pounded - and might not survive it. Like anything in a motor...glow plugs need breaking in also before they can take hard use. Always stay rich the first few runs with a new glow plug and give it a chance.

This used to be stated with every glow plug KB sold on the back of the package before the light went on that they shouldn't really be bragging how to lengthen the life of a plug. <_<

Remember also a glow plug should not really burn out that often. If treated in a modest tune, they should last past a couple jugs of fuel if not more. Some sport engines can go their whole life on it's original plug if it's kept in sport tune.

It is only when you step up to very high nitro (40%-60%) is when you start burning plugs every tank or so, because the coating on the coil is designed to react only with methanol...not nitromethane, and no setting will ever be correct for the plug to last any long length of time. Like they say, Nitro is pure dynomite...

BECAUSE THE COATING ON THE COIL IS DESIGNED TO REACT ONLY WITH METHANOL. ???????

 

[jetpack]

Yes, the glow plug element material only catalizes with methanol compounds.

 

[Jack ODonnell]

Yes, the glow plug element material only catalizes with methanol compounds.

WHERE ARE YOU GETTING THIS INFORMATION FROM. ?

 

[jetpack]

Platinum which is either coated to the coil wire, or the coil completely made from platinum (the better kind) can glow through catalytic reaction with methanol vapor, even with no other ignition source.

Castor oil, synthetic oil, nitromethane, ect cannot generate this reaction with platinum. Methanol vapor is unique in this respect with platinum, it is what enables glow plugs to work.

The closer you get to running 100% nitro, methanol content becomes less and less until your glow plug stops working or blows out gets destroyed. At this point, glow power isn't the right method of ignition, and you have to switch to a spark ignition system to make it happen.

 

[Jack ODonnell]

Platinum which is either coated to the coil wire, or the coil completely made from platinum (the better kind) can glow through catalytic reaction with methanol vapor, even with no other ignition source.
Castor oil, synthetic oil, nitromethane, ect cannot generate this reaction with platinum. Methanol vapor is unique in this respect with platinum, it is what enables glow plugs to work.

The closer you get to running 100% nitro, methanol content becomes less and less until your glow plug stops working or blows out gets destroyed. At this point, glow power isn't the right method of ignition, and you have to switch to a spark ignition system to make it happen.

I did not ask for the history, I asked where you got your information.

 

[jetpack]

I made it a personal study with my 9th grade physical science teacher, Mr. Norbert.

I was actively involved with building and flying 1/2A control line at the time, and the class book opened up to catilytic reactions one day. I brought up the subject of my glow heads and the rest is history, and we studied more into what platinum is all about. Helps make it one of the world's most precious metals.

 

[Rick Sowell]

wow all good information, thanks guy's, the plugs I have tried so far have been K&B 1L and HP also an MC9 and 59, about the same results with all, maybe a longer run before failure, but didn't keep track of that. I will check head clearence and then I will know that for future reference, the prop may be the problem as I can hear it lose speed in the corners and pick up when off the rudder on the straights. I will try a smaller prop. Ron said he used a V937/3 and said it was a little peaky on the pipe, the specs for that prop have way more pitch than I am running so I don't know if that will be a cure. I have a 215 and a 36/55 that I may have to try. all the info posted is a great help so far you guy's are awsome keep posting any comments as this will help other people as well. thanks again.

 

[Norm Doerr]

I would put a smaller prop on the thing, look at setup etc etc. The boat is loading up in the corners and making the engine work too hard. This may have already been covered in this thread, (I don't have time to read all this stuff). The glow plug is telling you something here. Rather then look at the plug as the problem.. look at what is loading the boat in the corners.. you put a big load on an engine and it wants more fuel goes lean and sags Again ... it is telling you something.

 

[Rokieboater]

Jack,

Can you shed some light on your experience/theories about glow plugs? Or at least your counter argument.

I am NOT Trying to start anything, rather just interested in your knowledge. It's apparent that you disagree can you tell us why?

Maybe start a new thread.

AGAIN, I am not interested in arguments, just knowledge.

Robert Holland

 

[Anders_Martinelle]

Mr Jetpack,

Distorted glow plugs come from either too much compression for the percent of nitro being used, too much load on the engine, or too much scavenging from the pipe like a lean condition. Its telling you it is a "timing" problem.

Hmmm, you will never kill a plug because of to high CR.

The thing that kill plugs are HEAT or a bad engine.

Find what is generating the heat and the problem solved.

Try lowering your compression, lengthening the pipe, or use a smaller prop and see what happens.

Do that but not lower the CR.....

Anders

 

[mtruex]

Mr Jetpack,

Distorted glow plugs come from either too much compression for the percent of nitro being used, too much load on the engine, or too much scavenging from the pipe like a lean condition. Its telling you it is a "timing" problem.

Hmmm, you will never kill a plug because of to high CR.

The thing that kill plugs are HEAT or a bad engine.

Find what is generating the heat and the problem solved.

Try lowering your compression, lengthening the pipe, or use a smaller prop and see what happens.

Do that but not lower the CR.....

Anders

the .12 motors dont like to lug a lot of prop, m440 is way too much, that is whats causing most of the problem..free up the boat and put a prop on that will spin easy,for 30% fuel somewhere in the 35mm range should get you going..then start shortening the pipe, .12s like to rpm..

i have also seen low timing and high CR cause this problem on the .12s with higher nitro