Plug eating monster = TT Pro 40...?  
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Plug eating monster = TT Pro 40...? - 9/26/2006 3:00:24 PM   
Jim Duda



Posts: 216
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		This is our 5th TT Pro 40 and it eats a plug after every run...engine is broken in and runs the same fuel and props as the previous four. Plugs in these four last an entire season!
Fuel = Powermaster 15% nitro, 18% lube-syn+castor blend
Props = 10-4, 10-5, 9-6 APC Sport series
Head shim = original .017 aluminum
Muffler = Stock, as supplied
Fuel Filter = Shadel's mini filter

Any ideas or suggestions?

< Message edited by Jim Duda -- 9/28/2006 3:54:07 PM >
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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 3:39:25 PM   
daven



Posts: 6908
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		burnt plugs are caused by either being too lean or overcompressed. I know you know how to set a needle, so look at your fuel system. I would suggest testing another tank with new fuel lines. If thats the stock head shim, you should be fine there.

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 3:40:33 PM   
fizzwater2


 

Posts: 800
Joined: 8/16/2004
From: Paola, KS, USA
Status: online 		If it was me, I'd try raising the head a little bit. Sounds like with all the machining tolerances, you may have one with higher compression than the others. Is the needle setting more particular on this engine?

What do the plugs look like when they come out? Can you take a pic of a plug and show us?

How about vibration? Is this engine on another plane, or have you run other engines on the same structure?

These all might be clues.. but a plug a flight is pretty extreme for 15% nitro

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 4:19:15 PM   
Jim Duda



Posts: 216
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		Dave & Fizz - Same plane as two other TT Pro 40s. Element is distorted and won't glow after one run. Launched at 800 - 1000 down from pinch. Top of piston (viewed through the plug hole in head) is shiney with No Discoloration. Fuel residue on fuse is light maple brown. Definitely not lean. Tank is Tettra 5.25 ounce. Needle is not sensitive at all.

I'll add a .003 or .005 or .008 head shim when I get some...

Plugs eaten so far: Thunderbolt 4 cycle (my favorite), K&B 1L, Tower long (no idlebar)
Ignitor used = Sonic Tronic twist and lock. (We don't use the Radio South ProDrivers on these plugs as they are kicked up for the Nelson plugs.)

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 6:01:34 PM   
fizzwater2


 

Posts: 800
Joined: 8/16/2004
From: Paola, KS, USA
Status: online 		A distorted plug sounds like high compression to me, but then, I've been wrong before..



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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 6:31:04 PM   
Jim Duda



Posts: 216
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		I'm lazy so the first thing I'm gonna do is install another plug gasket to raise the plug. If that doesn't help then I'll do it the correct way:
Mic the deck clearance;
Mic the depth of the head with no shim installed;

Compare those dimensions with similar measurements from another engine.

Higher than normal compression sure seems likely...

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 7:18:58 PM   
daven



Posts: 6908
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		It sounds like its overcompressed, but what are the odds??

I'm betting you got a leak somewhere in a fuel line or the tank and your sucking air.

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 7:42:41 PM   
fizzwater2


 

Posts: 800
Joined: 8/16/2004
From: Paola, KS, USA
Status: online 		are the plugs coming out dry and sort of burned looking, or are they slightly oily and just distorted? Take a good look at the plugs, see what they're telling you.

I think High Plains had a post a while back about reading plugs, a skill learned in Formula 1 racing where it was normal to burn a plug a flight.. you could read the plugs and get clues about your compression, needle setting, etc. You might search a little for that, see if it helps any.

Have you swapped engines on this plane, using the same tank and fuel line setup? If the other engines run fine, that might help rule out fuel tank problems. Maybe there's an air leak under your carb on this engine?



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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 7:55:07 PM   
Jim Duda



Posts: 216
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		Slightly oily but definitely distorted...two other TT PRO 40s with same lines, filter, tank, fuel = NO PROBLEMS. Air leakage under carb = lean...see comments below.

Professor Dave - sucking air would equate to a LEAN mixture...correct? Engine does not "sag" or lose RPMs in sustained up lines. No baked on fuel residue on fins or muffler which are indicators of lean (hot) runs. Tettra has no fuel outside the bladder so tank is OK.

Place your bets...

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 8:12:47 PM   
fizzwater2


 

Posts: 800
Joined: 8/16/2004
From: Paola, KS, USA
Status: online 		I would vote either overcompressed, since the plug doesn't seem to indicate lean (it would be drier) and it's distorted.

Have you noticed much difference in the way the engines run? Is this one significantly higher or lower RPM on the same prop as your other ones? Look very carefully at the oil residue on the side of the plane, are there any teeny metal flecks in it? Perhaps something is rubbing - foreign matter might be distorting a plug, too, but I'm thinking it's probably overcompressed a bit.

Check your head clearance, let us know what you find, I'm curious!


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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 8:30:07 PM   
daven



Posts: 6908
Joined: 12/7/2001
From: Andover, MN, USA
Status: offline 		Yes, sucking air would cause it to go lean, but it doesn't sound like thats your problem. Its gotta be overcompressed, measure and let us know.

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 8:34:08 PM   
Jim Duda



Posts: 216
Joined: 4/10/2006
From: Austin, TX, USA
Status: offline 		Calling Sherlock Holmes...calling Sherlock Holmes!

A distorted element many times will still glow when excited electrically...NONE of the half dozen or so dead plugs will. I find that very strange... Again, the ignitor I'm using causes just a medium orange glow to the elements so excessive voltage is not the culprit.

I just need to get off my butt and measure it.


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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 8:59:20 PM   
fizzwater2


 

Posts: 800
Joined: 8/16/2004
From: Paola, KS, USA
Status: online 		are the elements being shoved up into the plug, or over to the side? If they're against the side maybe they're shorting out, so they won't glow..

i'll stay tuned, I'm interested in what you find when you measure head clearance.



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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 9:25:07 PM   
HighPlains


 

Posts: 2666
Joined: 3/2/2003
From: Over da rainbow, KS, USA
Status: offline 		I'd check the bearings. If one of the balls is starting to spall, the nearly microscopic bits of metal will take out plugs about as fast as you put them in.

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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 9:31:12 PM   
fizzwater2


 

Posts: 800
Joined: 8/16/2004
From: Paola, KS, USA
Status: online 		howdy, high plains! I wondered about that myself, hence the comment about looking for sparkles in the oil on the side of the plane. A "light maple brown" color on the side of the plane after a flight might be a clue here we've not given much attention to. Usually the oil residue on the side is pretty much oil colored.. brown might indicate some sort of rubbing, bearing failure, etc.

How's life out there in the "high plains" of western Kansas? Too much working going on here in Eastern Kansas. I'm hoping to take my son, my step son, and a co-worker and two of his boys out this Saturday to fly the senior Kadet, hope there isn't too much wind!



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RE: Plug eating monster = TT Pro 40...? - 9/26/2006 11:26:19 PM   
DHG


 

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From: Arvada, CO, USA
Status: offline 		Wind? In Kansas? Surely you jest.

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