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Author Topic: Merlin Glow Plugs  (Read 2330 times)

Offline Dave Moritz

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Merlin Glow Plugs
« on: January 17, 2021, 08:10:51 PM »
I see that Brodak has their hot, 4-stroke plug in stock. Anyone tried it yet?  Is it the same thing as the Merlin 2004?

Dave Mo...
It’s a very strange world we live in, Master Jack.” (4 Jacks and a Jill)

Offline Robert Zambelli

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Re: Merlin Glow Plugs
« Reply #1 on: January 17, 2021, 09:30:16 PM »
Hi, Dave - news to me.
Although I'm familiar with many of the Brodak products, I had no idea that Merlin made a 4S plug. I thought Brodak sold only the OS 4S plugs.
BUT, looking at the photo in the website catalog, it does not look like the 4S plugs I normally use - no protrusion.

If you decide to try one, please post your results/opinion.

Bob Z.

Offline Lauri Malila

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Re: Merlin Glow Plugs
« Reply #2 on: January 17, 2021, 11:39:04 PM »
Btw, what would be the closest replacement to Merlin #2004 hot plug. I really like it a lot (or my engine likes).
I still got a decent stock but it won't last forever...

Lauri

Online Massimo Rimoldi

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Re: Merlin Glow Plugs
« Reply #3 on: January 18, 2021, 12:18:50 AM »
Hi Dave.
A few years ago, Al told me that plug #2004 and #2009 had the same filament, only #2009 had a longer nose.

I hope this helps, Massimo

Offline Dave Moritz

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Re: Merlin Glow Plugs
« Reply #4 on: January 19, 2021, 08:43:31 AM »
Hello All:

Thanks for the responses. It looks like the blind leading the blind here. I'll place some on order soon and provide what feedback I'm capable of.

All the best.

Dave Mo...
It’s a very strange world we live in, Master Jack.” (4 Jacks and a Jill)

Offline Dennis Moritz

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Re: Merlin Glow Plugs
« Reply #5 on: January 27, 2021, 03:46:11 AM »
Common to use RC plugs in control line stunt. Try a few. At one time they were reasonably priced. Owner of Merlin passed a while back. Don't know how that effected availability or price. Our club has favored Thunderbolt RC plugs for years. We are absolutely certain they are the best. Might be a cult illusion and opinion.
« Last Edit: January 27, 2021, 08:53:15 AM by Dennis Moritz »

Offline Dan McEntee

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Re: Merlin Glow Plugs
« Reply #6 on: January 27, 2021, 07:34:37 AM »
   I don't know anything about the Brodak offerings, but I use GlowDevil R/C Long plugs for the most part and have been for many years. I also have some Thunderbolt R/C long plugs in my stash also. I use an R/C with idle bar plug because it helps protect the element, and gives carbon some place to grow and can be cleaned off if necessary.  What makes a plug a "hot" plug is the length of the element and the size of the opening the element is in. The longer the element and bigger the chamber means a more fuel to mix with the element and that makes a hotter plug. Four stroke plugs are hotter because they often have that extra stub at the bottom of the plug to make the chamber longer. The best way to tell if a plug works or not is to just try one.  pages and pages of discussion have been done on this subject and search is in order to read more.
   Type at you later,
  Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline Dave Moritz

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Re: Merlin Glow Plugs
« Reply #7 on: February 14, 2021, 08:36:31 AM »
I've now got in my hot little hands a Merlin plug (also hot) from Brodak. It is the long, four-stroke version with the extended snout and red color around the post. Apparently it is old stock and when Brodak is out, they'll be out for good.

Dave...
It’s a very strange world we live in, Master Jack.” (4 Jacks and a Jill)

Offline Dan McEntee

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Re: Merlin Glow Plugs
« Reply #8 on: February 14, 2021, 09:46:14 AM »
I've now got in my hot little hands a Merlin plug (also hot) from Brodak. It is the long, four-stroke version with the extended snout and red color around the post. Apparently it is old stock and when Brodak is out, they'll be out for good.

Dave...

    Now that you have a good example, compare it to another plug, standard and four stroke, to see the difference in the coil size and the size of the chamber. I think the four stroke plugs with the extended snout have this to get a deeper chamber for a longer coil to make it extra hot. the bigger, deep chamber holds more fuel for a bigger reaction.
    Type at you later,
    Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline BillP

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Re: Merlin Glow Plugs
« Reply #9 on: February 14, 2021, 04:04:35 PM »
The plugs I've checked under a lab microscope show hots have smaller diameter wire than colds. Didn't pay attention to chamber size.
Bill P.

Offline Fredvon4

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Re: Merlin Glow Plugs
« Reply #10 on: February 15, 2021, 11:44:20 AM »
By examining "hotter" and "cooler" spark plugs of the same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have more substantial ceramic insulators filling the gap between the center electrode and the shell, effectively carrying off the heat, while the hotter plugs have less ...

The difference between hot and cold glow plugs is the amount of heat they hold. By changing the glow plug from cold to (let's say) medium, ignition timing will change - will happen faster in the cylinder (given that you don't modify the needle settings), or will happen at a lower pressure

For the most part, the type of fuel you are running will impact the kind of glow plug you need to use. ... In general, the higher the the nitro percentage, the colder the plug should be. Conversely, the lower the nitro percentage, the hotter the plug should be.
"A good scare teaches more than good advice"

Fred von Gortler IV

Offline Lauri Malila

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Re: Merlin Glow Plugs
« Reply #11 on: February 15, 2021, 12:07:04 PM »
By examining "hotter" and "cooler" spark plugs of the same manufacturer side by side, the principle involved can be very clearly seen; the cooler plugs have more substantial ceramic insulators filling the gap between the center electrode and the shell, effectively carrying off the heat, while the hotter plugs have less ...

I'm sorry, but that's a little weird statement. Firstly, I have never seen a plug manufacturer varying the insulator depending the deat range. They stick with the same basic construction and alter the dimensions of coil and the cavity in which the coil sits. If you have seen differences between insulators, it's propably between different brands.
And the insulator thermal conduction plays a homeopathically small role anyway.
Secondly, if you have more insulator, wouldn't that make the plug more hot?🤔

Regarding 4-stroke plugs, technically they are hotter, but instead of thinner filament they have a longer (heavier)  coil with higher heat capasity. That helps them stay hot during the exhaust stroke.

Btw, I noticed that the so called Turbo Plugs are available in a huge variety of heat ranges. Does anybody know how their "hot" corresponds with our "hot" plugs? If they are similar, they might be an interesting option, plus you get a more intelligent combustion chamber shape with them. Turbo plugs are like Nelson plugs, but with a metric fine thread. Instead of a soft sealing ring, they have a conical sealing surface in the bottom of plug. L

Online Massimo Rimoldi

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Re: Merlin Glow Plugs
« Reply #12 on: February 15, 2021, 01:49:18 PM »
Hi Lauri.  Maybe the table provided by OS can be useful. Unfortunately using Turbo Plugs involves modifying the engine head, but maybe you know a good machinist who can do the job ....

Massimo
« Last Edit: February 15, 2021, 11:35:55 PM by Massimo Rimoldi »


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