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Glow plugs dying per tank of fuel

Glow plugs dying per tank of fuel

Old 02-20-2014, 08:47 AM
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Default Glow plugs dying per tank of fuel

Background info:
Engine: OS 30VG - fully sealed engine using Merlin 2006 glow plugs, and broken-in with Byron 25% nitro with 11% lubrication - engine ran like a champ and didn't destroy glow plugs every tank of fuel

I had to switch to this fuel due to the hobby shop no longer carrying my old fuel. New fuel: Byron 30% nitro with 11% lubrication

After switching to the new fuel, the engine required some additional tuning. At this point, the engine will run great for 200cc of fuel (sufficient blue smoke, sounds good, good power at low and high end, temps are 240-250F), but after that, it will not idle nor stay running... I switch out the glow plug with a new one and vuala, the engine runs just fine for another 200cc of fuel. Upon glow plug examination, there is very very small amounts of moisture left over on it and it turns slightly silverish after running. I'm probably running 1/24 too rich. The glow plug does have a burn on the coil that's probably 1/10mm long and the plug still lights up the way it should (see pictures below). My concern is the 1/10mm burn in the coil that I'm guessing is likely causing my problem but I don't know what's causing it to happen.

I tried running an OS A5 and that provided the same performance as the Merlin 2006's and it still produced the same results after 200cc of fuel.

New glow plug is on the left; used glow plug that's had 200cc of fuel run through it is on the right.



What do you guys think is the problem? Thanks for the help.
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Old 02-20-2014, 04:01 PM
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Without knowing your tuning experience and how you tune it's hard to say. First thing comes to mind is try adding a .10mm shim.
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Old 02-20-2014, 04:03 PM
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Too much compression. Need to add a head shim. Engine could also have a stretched/worn rod.
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Old 02-20-2014, 04:48 PM
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Just for the hell of it. Put in a new plug. Run the engine for 200 cc, then let it cool down completely and then try again without changing the plug and see how it runs.

Last edited by Austin's dad; 02-20-2014 at 05:04 PM.
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Old 02-20-2014, 06:01 PM
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I'll pickup a shim from my LHS and give that a shot. Thanks for the help guys. I'll post back any new results.
Originally Posted by Austin's dad View Post
Just for the hell of it. Put in a new plug. Run the engine for 200 cc, then let it cool down completely and then try again without changing the plug and see how it runs.
Same results occur.
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Old 02-22-2014, 08:11 AM
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In my experience, when glow plugs burn out this fast, it's running too lean.

Try to richen the bottom and top by 1/8 turn. Even if it seems sluggish, just test this out to see what happens. If it still burns out the plug, try to richen one more 1/8 turn. If it still burns out, take the head off the engine and look for any small pebbles that might be bouncing around in the engine.
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Old 02-22-2014, 05:21 PM
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The pics are of the OS A5 plug right?

Reason I ask is the OS A5 ( OS No. 10 ) Is one of the coolest running plugs you can get from OS ( Suggested use in Flying RC because of the air cooling effect on motors keeps them consistently and evenly cooled.) Running around 210 would be the most I'd subject that plug too, I'd imagine running hotter than that with a higher Nitro content would most definitely foul the plug

Simply put your engine is running FAR hotter then the plug filament is rated for in my opinion.

If you haven't already, Try the OS #8 Medium Plug, This OS plug is specifically used in the OS VG.30.

Hope that can help, If the problem persists I doubt it's the fault of your plug, and more to do with the fuel mixtures from your high/low/idle needles.
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Old 03-03-2014, 02:44 AM
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Most people us a rule of thumb that Hot plugs are better for bigger engines and faster engines.
That plug is probably way too cold. Especially for off road use.
http://www.osengines.com/glowplugs/
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Old 03-03-2014, 08:32 AM
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Are you wiping the plug off before you take the picture. I don't see any slight brownish color or slight oil residue. You an tell a lot about the tune oft he engine by looking at the plug.
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Old 03-04-2014, 12:10 PM
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Merlin 2006 glow plugs are hot.

Im with Frank. Those plugs do not look like they been ran. After one tank in my car, you could tell a used plug from a new plug.

By running one tank of fuel it sounds like it happens when the engine gets hot.

I would suggest going back to factory settings on the engine. With no residue on the glow plug, I wanna say, you are running super lean some where. Just a guess, because Im not there, but, picturing it in my brain say, your running rich on the bottom (getting smoke) and super lean on top. Just my thought.
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Old 03-04-2014, 06:54 PM
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Originally Posted by token View Post
Merlin 2006 glow plugs are hot.

Im with Frank. Those plugs do not look like they been ran. After one tank in my car, you could tell a used plug from a new plug.

By running one tank of fuel it sounds like it happens when the engine gets hot.

I would suggest going back to factory settings on the engine. With no residue on the glow plug, I wanna say, you are running super lean some where. Just a guess, because Im not there, but, picturing it in my brain say, your running rich on the bottom (getting smoke) and super lean on top. Just my thought.
the 2006 plug is considered cold according to merlin.
http://www.merlinglowplugs.com/Car.html

I would try the 1998 plug
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Old 03-05-2014, 05:03 AM
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I hate to tell you this but it sounds to me like it's time for a pinch.
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Old 03-31-2014, 01:15 PM
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I tried richening it up and couldn't get it to tune right. I reset my needles and tried to retune and couldn't get it to tune without blowing through glowplugs. My LHS got some more 25%/11% Byron fuel in. Upon resetting my needles and retuning, the thing runs like a champ now and doesn't burn through glowplugs. Thanks for the help guys.
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Old 04-02-2014, 02:14 AM
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You switched | increased ... nitro % without adding a head shim - too much compression.

Should run 30% anyway ... more power at cooler temps. All you needed was a head shim. [ most likely ]
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Old 04-02-2014, 09:06 AM
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Originally Posted by Hoese37 View Post
Too much compression. Need to add a head shim. Engine could also have a stretched/worn rod.
Originally Posted by SoCalTazer View Post
You switched | increased ... nitro % without adding a head shim - too much compression.

Should run 30% anyway ... more power at cooler temps. All you needed was a head shim. [ most likely ]
+1
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