Spark Plug question

AstoN_B · 13-03-2010, 02:10 PM

For a friend.

His rally car keeps burning spark plugs out, sometimes two sets in a days rallying sometimes not at all. It the porcelain bit that burns not the spark tip.

He's been using NGK TR5a/10 as thats what parts place said would be best.

Car is a Mk3 fiesta with 1.6engine but 2.0 head apparently.

What plugs would be better to try? I thought some with higher temp range unless theres too much power coming to plug which is burning it out?

Never heard of that though

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tabetha · 13-03-2010, 04:57 PM

What precisely do you mean by burn.
If it was getting hot enough to melt the porcelain you'd have no engine well before that, as it would have melted first.
Porcelain is normally made from Kaolin, which is aluminum hydrosilicate, this is fused with white quartz, well specifically feldspar, at a temperature of 1300-1400 C.
Even soft procelain needs 1100C to melt.
It can be pitting or something else though, really need to see a plug.
tabetha

AstoN_B · 14-03-2010, 04:56 PM

Only problems I've heard of are where the porcelain comes loose from the threaded body.

It appears to be orangey brown where the lead plugs on. That's the description I got. I'll try and get a picture in next couple days cause it's at his lockup unles he's got an old set.

Any ideas so far?

tabetha · 14-03-2010, 06:15 PM

The orange colour is okay, it's called corona discharge, you get it where high voltage and electric conductive liquids are in close proximity, usually oil fmes is enough to do it, they get attracted to the porcelain and cause the staining, if it gets like streaky lightning looking though this is discharge through the body gap between porcelain and metal, not good need throwing away.
As to why they become loose in the body is a mystery, only ever had that once in 25+ years.

AstoN_B · 16-03-2010, 10:08 AM

I'll have a proper look when it's next out. Hopefully somethng of nothing. Didn't ask whether there was a misfire too. Probably is just some oil vapour, maybe something in the lead plug.

If I get chance I'll get a photo.

13-03-2010, 04:57 PM	#2
tabetha BANNED BANNED Garage is empty, add now Trader Score: (0) Join Date: Jul 2006 Location: uk Posts: 24,646 Rep Power: 0	What precisely do you mean by burn. If it was getting hot enough to melt the porcelain you'd have no engine well before that, as it would have melted first. Porcelain is normally made from Kaolin, which is aluminum hydrosilicate, this is fused with white quartz, well specifically feldspar, at a temperature of 1300-1400 C. Even soft procelain needs 1100C to melt. It can be pitting or something else though, really need to see a plug. tabetha Last edited by tabetha; 13-03-2010 at 05:03 PM.

14-03-2010, 04:56 PM	#3
AstoN_B An eye for detail... 1989 Ford Escort Trader Score: (1) Join Date: May 2009 Location: Preston Posts: 762 Rep Power: 3	Only problems I've heard of are where the porcelain comes loose from the threaded body. It appears to be orangey brown where the lead plugs on. That's the description I got. I'll try and get a picture in next couple days cause it's at his lockup unles he's got an old set. Any ideas so far? __________________ *'89 Diamond White XR3i EFi daily/fast road/show car:* 90 spec, 4-2-1 tubular manifold, Piper 285 cam & 2" stainless exhaust, poly bushed, Spax adj all round, Tarox Strada pads. Cossie lattice's being refurbed for track sessions. *'88 XR3i Cab project:* Custom ITB's, Manifolds and Blacktop conversion, IB5 with Group N gear set + millions of details! Needs finishing ASAP as its gone on too long

16-03-2010, 10:08 AM	#5
AstoN_B An eye for detail... 1989 Ford Escort Trader Score: (1) Join Date: May 2009 Location: Preston Posts: 762 Rep Power: 3	I'll have a proper look when it's next out. Hopefully somethng of nothing. Didn't ask whether there was a misfire too. Probably is just some oil vapour, maybe something in the lead plug. If I get chance I'll get a photo. __________________ *'89 Diamond White XR3i EFi daily/fast road/show car:* 90 spec, 4-2-1 tubular manifold, Piper 285 cam & 2" stainless exhaust, poly bushed, Spax adj all round, Tarox Strada pads. Cossie lattice's being refurbed for track sessions. *'88 XR3i Cab project:* Custom ITB's, Manifolds and Blacktop conversion, IB5 with Group N gear set + millions of details! Needs finishing ASAP as its gone on too long

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14-03-2010, 06:15 PM	#4
tabetha BANNED BANNED Garage is empty, add now Trader Score: (0) Join Date: Jul 2006 Location: uk Posts: 24,646 Rep Power: 0	The orange colour is okay, it's called corona discharge, you get it where high voltage and electric conductive liquids are in close proximity, usually oil fmes is enough to do it, they get attracted to the porcelain and cause the staining, if it gets like streaky lightning looking though this is discharge through the body gap between porcelain and metal, not good need throwing away. As to why they become loose in the body is a mystery, only ever had that once in 25+ years.

16-03-2010, 10:08 AM
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