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Post  Iceberg on Wed Mar 06, 2019 7:32 pm

I have a merlin head and glow plug. When I run it on various engines it seems to run really good for maybe 30 seconds then kind of fluctuate and then get back into business. Then I change out for a standard or high comp cox glow plug and it runs true without any fluctuation until tank empty. I needed to add four copper head gaskets until it would start ok. I guess that the compression is higher on the Merlin accounting for the multiple copper shims required. I have wondered if any other suggestions are out there that would help as regards why this head might fluctuate while running but the Cox one does not do that?

Thanks
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Post  Mark Boesen on Wed Mar 06, 2019 7:51 pm

How does it run with five gaskets? Over compression will cause a engine to sometimes run erratic, as is a hard to needle engine.
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Post  1/2A Nut on Wed Mar 06, 2019 10:49 pm

Is that a flat coil glow bee plug? So this is the insert type with an adapter plug?
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Post  Iceberg on Thu Mar 07, 2019 2:06 am

Yes it has a coil similar to the cox ones but has a separate insert piece that threads over it. I've only tried 4 head gaskets I'll try 5 gaskets tonight and see.
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Post  Iceberg on Thu Mar 07, 2019 4:21 am

Well I put 5 shims and then went to 6 shims. I actually ran pretty good but still had some slight rpm wavering? I took off the two blade 5x3p and put a three blade 5x3.5p. That was what ran pretty good. Prop wash was also good. Dare I try seven shims? Seems loosing a lot of compression?
Thanks
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Post  KariFS on Thu Mar 07, 2019 5:00 am

Could it be that the engine just "wants" more load? The other prop has one more blade and higher pitch. Do you have an even bigger prop to try with?

5x3 sounds kinda small for a hopped up engine, although I am far from an expert on this.

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Post  1/2A Nut on Thu Mar 07, 2019 5:02 am

Here is the flat coil insert type no hole for the element greatly improves compression.
That is weird stuff going on on your end I can get by with 1 shim and a nelson plug with my TD engines
What kind of engine are you running over there?

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Post  Iceberg on Thu Mar 07, 2019 7:29 am

The plugs I have are like the one you show on the right with the purple color. I am going to try a 6x4 tomorrow with the Merlin head. The motor is a real nice venom looking block. Fred sent over. I ran a 6x4 yesterday with standard coz head. Ran great just a touch slower.

Yes 6 or 7 shims didn't sound right to me.
Thanks
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Post  RknRusty on Thu Mar 07, 2019 1:17 pm

Hey, Ice. It's not unusual to need 5 head gaskets with those drop-in plugs. Especially with a fairly new engine that has good compression already. In fact I usually advise people to start with 5 and work from there. That is a good head and plug combination though. I run them on all of my Cox engines. And on Norvels when they need replacing.
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Post  NEW222 on Thu Mar 07, 2019 4:30 pm

Hey there 1/2A Nut. Question time for you! Where on earth did you ever find the flat coil plugs? Also , who the heck makes those. I have nover seen nor heard of those before your mentioning it along with pictures. That looks kind of funny, but interesting. Thank you.
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Post  1/2A Nut on Thu Mar 07, 2019 5:43 pm

Without the hole in the plug you get better compression is one reason for the flat coil
another is it spreads the heat further out across the top of the piston for bigger burn
more bang / power. The flat coil element is more robust and can handle higher nitro
lasts longer and handle higher compression. Great for competition engines.
Merlin Glow Bee Plugs. Owner died the family is not currently selling the plugs.
Now the site has been closed down here is the old link:

http://www.merlinglowplugs.com/Aircraft.html

New link modified with the following message:

http://merlinglowplugs.com/

Some sites still have old stock but Merlin also made conventional plugs. The sites
i have found that had stock did not have flat coil types all those have been sold out.

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Post  NEW222 on Thu Mar 07, 2019 7:17 pm

Very interesting. Thanks for the information. Too bad they are no longer available. Funny to me though as one would think someone else would try to produce them. I could see the benefits now though.
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Post  Mark Boesen on Thu Mar 07, 2019 11:17 pm

Iceberg wrote:Well I put 5 shims and then went to 6 shims. I actually ran pretty good but still had some slight rpm wavering? I took off the two blade 5x3p and put a three blade 5x3.5p. That was what ran pretty good. Prop wash was also good. Dare I try seven shims? Seems loosing a lot of compression?
Thanks
Ice RC Plane


-Make sure there's no varnish on cylinder?
-needle is not leaking, add a short piece of tubing to needle base. Remove needle and wipe, sometimes crap will cause wavering.

-no air leaking on backplate?
-decent gasket on airtube?
-Is it a new engine, it just might need some time?
-What is the nitro and RPM you're getting? What is the 5x3 you're using? Is it flexing?
-welcome to the fun world of 1/2a's!
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