Houston...we have CONTACT! UPDATED 09APR

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CobraSix

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Well...got some bad news today. For somereason, my #1 spark plug is getting hit by either a valve or the piston. It's just barely hitting, because there is almost no marking on the plug, and it only closes the gap from .055 to .015. It's hitting the curved part of the electrode. I guess I'm going to try another plug and index it so it has the electrode point sideways.

I guess my block has been decked...should have measured it. Oh well, live and learn.

Slade
 
Somehow, I suspect this may relate to your poor gas mileage.
 
How much was your head decked what pistons are you running. I have a cut up log head off a 250 and the chambers are not deep at all.
 
Sorry to hear it has happened, Slade. This is a first in my "experiences database" with the sixes.

I suspect Tim is onto someting, maybe in conjunction with a long nosed plug. Are you running a composite gasket?

We could benefit from a full troubleshoot!

Adam.
 
Running a thin head gasket with a head milled at least .030 (48cc for chamber volume on an Aussie head). it's only on the #1 piston though...that's kind of the odd part. Like I said, I think it's just the curved part of the prong sitting too far it. I mean, the amount of movment required to bend the prong is only like .010. smaller then the amount of the gap closing. I do think finding a plug that has slightly different threads that make the electrode horizontal vice verical will clear up the problem.

Slade
 
Or you could try adding another spark plug washer from a spare spark plug, indexing it and see if that gives you the 1/4 turn you need.

Bummer of a problem, I hope the simple fix works.
(48cc for chamber volume on an Aussie head).
Click to expand...
What is your C/R? Maybe you could benefit from a composite head gasket without lousing too much compression.
 
Well, with the head milling, I thought 9.5:1. This spark plug issue makes me wonder about the decking of the block...so maybe higher.

Slade
 
:shock: 48cc? From memory they start at about 58 or so!!! You have taken a good few thou off. And they were made for the thicker (intermediate style) head gasket... I reckon there'll be a shorter plug that'll do the trick.

Cheers, Adam.
 
Before you suspect your machining, and based on the fact that it is only one spark plug, do you have predetonation?That can close the gap on a plug too. Try to see into your cylinder with the piston at TDC and see if you see and damage on the top of the piston. Detonation can cause little pieces of the piston crown to nick off and hit your sparker tip.

Good luck, Duane


CobraSix said:
Well...got some bad news today. For somereason, my #1 spark plug is getting hit by either a valve or the piston. It's just barely hitting, because there is almost no marking on the plug, and it only closes the gap from .055 to .015. It's hitting the curved part of the electrode. I guess I'm going to try another plug and index it so it has the electrode point sideways.

I guess my block has been decked...should have measured it. Oh well, live and learn.

Slade
Click to expand...
 
Engine is running really well, even with the closed gap. here is a picture of the plug:

number1a.jpg

number1b.jpg


The rest of the plugs use this:

number4b.jpg


I am wondering if I do have contact, wonder if I have valve contact too.

Slade
 
Okay not to get off on another subject (I just have to ask) but with that high of compression, what grade gas are you using?

Sorry, but I'm not trying to open a can of worms but I was just wondering is all.


-Chris
 
Actualy Chris, you might be on to something, like I stated above with the detonation......
Duane

stang200 said:
Okay not to get off on another subject (I just have to ask) but with that high of compression, what grade gas are you using?

Sorry, but I'm not trying to open a can of worms but I was just wondering is all.


-Chris
Click to expand...
 
There are contact marks on the plug. I'll pull and take some pictures when I go home.

I am running 92-93 octane. I'm really kind of concerned with the decking, but I figured I'd have issues with the other plugs too.

Slade
 
HI
Just one other quickie.. is this the first time you notice this or has it happened more than once on that cylender??
Maybe you just for got to gap that one??
Tim
 
I've gapped it 3 times. I thought that when I first noticed it...figured I forgot to gap. Regaped it, next day, pulled it again, and flattened again.

I'll try another brand.

Slade
 
How did you get that plug to burn that color mine are grey almost black with unleaded petrol.
 
Tim,

Sounds like you are running rich then. I think I may be just a little on the lean side. Plan on jetting up 1 or 2 sizes.

Slade
 
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