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  #1 (permalink)  
Old 08-07-2013, 06:38 PM
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Cobra Make, Engine: Butler Cobra. 350 Chevy Engine, blueprinted, heads cc'd, ported, polished, manifolds matched, big valves, 1.6 roller rockers, TB Injected, mild cam, MSD crank trigger electronic ignition. TKO-600 transmission. XKE Jaguar rear. IFS by Fast Cars
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Default Butler Cobra. Spark plug boots melting

I've just got my Cobra running and have been driving it for three weeks and I'm sorting out any problems before I dismantle the car and do the body work and paint. Car is FANTASTIC and I'm LOVING it.

But I do have a problem with the number 2 and number 7 spark plug rubber boots melting as these are too close to the headers. Headers are original butler.

I have a 350 Chevy Small block with 202-160 iron heads, 62/64cc combustion chambers, straight plugs. These similar to Z28 and Corvette of the 1970-tees era. Camel Hump I believe.

I'm using Champion RJ12YC spark plugs that are one of the suggested plugs for this engine and thought I had a great solution with trying to switch to the NKG 2057 BPM8Y plugs which are 3/4" shorter than the Champion. Only problem is when these are finger tightened into the head, the hex of the plug ends up below the recess of the counter bore of the plug hole and there is no room for a socket wrench to fit to tighten it. So back to square one.

Has anyone had this problem. And how did you solve it.

Does anyone know if shorty 5/8" hex spark plug is available in a crush washer style that will fit this head. Also what is the design criteria that dictates when a tapered seat plug can be used. My heads have a nice 45 degree chamfer around the tapped spark plug hole that looks like a perfect mating surface for a tapered plug seat. The plug thread is 14mm X .375" (3/8") thread length.

BTW. Headers are wrapped with header wrap and the insulation is touching the spark plug boots on number 2 and number 7 plugs.

PS. The car LOVES the engine, so please don't hurt my feelings with wise cracks on my non traditional engine. It just a Hot Rod after all.

Thanks, Arthur

If you'd like to see my build photos click on the link. I hope you enjoy it. https://www.facebook.com/media/set/?...1&l=0d9c5c8c6d

Last edited by lal Naja; 08-08-2013 at 04:20 PM.. Reason: Adding link to photo show, typo, more info.
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Old 08-07-2013, 08:35 PM
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I've had that same problem. You need the proper plug for the threads in the head and the proper heat range for the combustion ratio. I now use MSD spark wires with straight boots that can be bent at an angle away from the header tubes. They have helped but #7 is still a little crispy.
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Old 08-07-2013, 09:56 PM
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Congratulations Arthur on getting your baby up and running.

I wonder how many other Cobra owners have faced up to the many small challenges you have in building the car single-handedly. More than just knowing every nut and bolt, you must know every thread and torque setting.

I'm sorry I can't offer any advice on your spark plug problem -- perhaps Craig will chip in with a suggestion. BTW he says too that the small block Chevy is perfect in his Arntz. He says the car is for sale but it seems to me that he's not trying too hard to shift it!! It's become his daily driver and he's having way too much fun with it.
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Old 08-07-2013, 09:57 PM
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Insultherm Spark Plug Boot Insulators - Fiber Glass Sleeving


I've used these for years, they work very well and are the least expensive.

Chevys typically use a short 90 degree boot with the wires below the header tubes.
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Last edited by Rick Parker; 08-07-2013 at 10:16 PM..
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Old 08-07-2013, 09:58 PM
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Thank you Tom, I'll look at your suggested MSD boots.

I currently have very tight 90 degree boots and I'm guessing that from the top of the spark plug terminal to the outside of the rubber is less than 3/16".

I've just thought of an ides that may give me a little more space. I can reduce the height of the spark plug terminal by cutting off half of it. The terminal in the spark plug boot that clips to the spark plug is only about 3/16in depth. And off the top of my head, that will give me about 3/16" to 1/4" of air space. I'll check tomorrow when I have a spark plug in my hand.

The plug I'm using now is a recommended plug for the heads. However I think for city driving I may need to go one step warmer.

Arthur

Last edited by lal Naja; 08-07-2013 at 10:05 PM..
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Old 08-07-2013, 10:30 PM
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Rick, thanks for the tip. I've considered these but am hoping to find a shorter spark plug. In the mean time I'll use these sleeves for protection. I hope these will fit my Taylor 90 degree boots. The link shows the type of boot I'm using. You can also see the boot in my Facebook Album.

http://www.speedwaymotors.com/Taylor...sal,14931.html

Thanks, Arthur

Last edited by lal Naja; 08-07-2013 at 10:47 PM..
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Old 08-07-2013, 10:43 PM
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Thank you Don, It's great to be driving the car. It's performance is outstanding. And yes I'm intimately connected to all the mechanical and electrical features of the car.

I still have a lot to learn about the Holley Commander 950 Pro EFI. It has been a huge learning curve and I've been plodding trough the program and manual to become proficient. I had no idea it was this difficult. And yes! it has been the most difficult part of this build.

Arthur
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Old 08-08-2013, 04:47 AM
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Nice job! I love the rollbar grommets. Would you be interested in making another set?

I looked at my car and my wires are run underneath the headers and come up behind the engine to the distributor. Nothing comes close to the exhaust at all and no wires are laying on the valve covers.
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Old 08-08-2013, 08:08 AM
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Arthur----

The flow out of those cylinders are away from the spark plug a little bit and a pretty good sized dimple in the header tube wont hurt your performance( it might even increase the flow numbers!) Take a medium sized ball peen hammer and set it on the header tube where you need the clearance and tap it with another larger hammer to indent the tube for a bit more clearance----work it patiently (whats a 1/2 hour added to 10 years?)

Good to hear that you are driving it this summer-----
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Old 08-08-2013, 08:51 AM
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Quote:
Originally Posted by joyridin' View Post
Nice job! I love the rollbar grommets. Would you be interested in making another set?

I looked at my car and my wires are run underneath the headers and come up behind the engine to the distributor. Nothing comes close to the exhaust at all and no wires are laying on the valve covers.
Thanks for your appreciation on the rollbar bezels. Making these were far more time-consuming than anyone would ever expect, especially the oval one. And it may not be evident, but one of the other ones is also slightly oval. Sorry to say, I just don't have the time or the inclination to repeat this process to make another set.

Are your headers Butler original? Is your engine a Chevy?

I would have the same header to boot clearance if I were to run the wires underneath. Finding a shorter spark plug will certainly help me. I'm not giving up on this option as of yet.
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Old 08-08-2013, 09:06 AM
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Quote:
Originally Posted by Jerry Clayton View Post
Arthur----

The flow out of those cylinders are away from the spark plug a little bit and a pretty good sized dimple in the header tube wont hurt your performance( it might even increase the flow numbers!) Take a medium sized ball peen hammer and set it on the header tube where you need the clearance and tap it with another larger hammer to indent the tube for a bit more clearance----work it patiently (whats a 1/2 hour added to 10 years?)

Good to hear that you are driving it this summer-----
Hello Jerry, Yes I'm going to do some dimpling on the headers when I remove them from the car. There is insufficient room to be able to make even the slightest hammer tap.

I'm still going to pursue finding a shortie spark plug for a better fit. A 5/8" hex size spark plug would be necessary too. I'm hoping I can use tapered seat plugs too, but I'm still trying to determine what the engineering/design criteria needs to be at the spark plug hole in the head to accept the taper seat plug.

BTY, I believe that running my new engine on the Dyno may not have beeen the best idea. Not sure what could have gone wrong but, I'm blowing a ton of oil out of the PCV 1 1/2 quart in 200 miles. You may recall that I built the engine back in 1987, perhaps parts/rings from that era may not react too well to the high reving stress. I think perhaps I should have followed the traditional break in procedure by driving some 500 to a 1,000 miles before a dyno run.

Hope al is going well with you,

Arthur

Last edited by lal Naja; 08-08-2013 at 04:38 PM..
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Old 08-08-2013, 09:55 AM
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I have the same problem with #7 plug being too close to the header. My problem is that it's arcing through the boot.
I am running these Accel shorty plugs http://www.summitracing.com/search/department/ignitions-electrical/part-type/spark-plugs/shorty-spark-plug/yes/make/chevrolet/engine-type/v8
I think I'll try the insulators that Rick suggested. I did try one fiberglass mesh sleeve from Summit and the boot still melted though it.
Any ideas on how to stop the arcing throught he boot? Have been using MSD boots as well as some hi-temp ones as well.
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Old 08-08-2013, 10:41 PM
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Interesting reading on plugs, wires, etc.

GrumpysPerformance.com • View topic - ignition wires & getting the header clearance
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Old 08-09-2013, 05:09 AM
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Quote:
Originally Posted by lal Naja View Post
Thanks for your appreciation on the rollbar bezels. Making these were far more time-consuming than anyone would ever expect, especially the oval one. And it may not be evident, but one of the other ones is also slightly oval. Sorry to say, I just don't have the time or the inclination to repeat this process to make another set.

Are your headers Butler original? Is your engine a Chevy?

I would have the same header to boot clearance if I were to run the wires underneath. Finding a shorter spark plug will certainly help me. I'm not giving up on this option as of yet.
I must have different headers as my car is an Arntz. I have at least 1.5 - 2" clearance between the wire and the header with a Chevy 350, angle plug heads, 90 degree boot running underneath. I will grab a picture later. I will check the plug type also as the boot covers the whole ceramic portion of the plug. My heads may be newer than yours as I believe they are from a 1984 1 ton truck.
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Old 08-09-2013, 05:35 AM
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Long live the Bow Tie COBRA. There is an article in this months Kit Car solutions for heat problems including spark plug wires.
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Old 08-09-2013, 07:51 AM
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Quote:
Originally Posted by joyridin' View Post
I must have different headers as my car is an Arntz. I have at least 1.5 - 2" clearance between the wire and the header with a Chevy 350, angle plug heads, 90 degree boot running underneath. I will grab a picture later. I will check the plug type also as the boot covers the whole ceramic portion of the plug. My heads may be newer than yours as I believe they are from a 1984 1 ton truck.
Angled plugs would make a difference for sure.

Knowing what plugs you're using may also be worth knowing.

I'm still trying to determine what the engineering criteria is on a spark plug hole to enable the use of a tapered seat plug. I've read that some heads in the era of mine were designed for both types of plugs.

Looking at the spark plug hole on my heads makes me believe that angled seat plugs may work. The chamfer around the plug hole seems like a perfect mating surface. See photo of my spark plug hole in the link below.

http://m1283.photobucket.com/albumvi...IokUH0sw%3D%3D

Last edited by lal Naja; 08-09-2013 at 07:55 AM.. Reason: add link
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Old 08-09-2013, 12:39 PM
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I will get you the plug number, but I can say I seem to have a lot more threads in mine than you do and my heads have a tapered plug with no milled flat for a washer. I think my plug would sit way too deep in the combustion chamber from the looks of it. I will measure the thread length tomorrow.

I didn't realize you had straight plugs. That is the difference. Mine plugs are angled kind of down and in.
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Old 08-09-2013, 02:57 PM
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Quote:
Originally Posted by joyridin' View Post
I will get you the plug number, but I can say I seem to have a lot more threads in mine than you do and my heads have a tapered plug with no milled flat for a washer. I think my plug would sit way too deep in the combustion chamber from the looks of it. I will measure the thread length tomorrow.

I didn't realize you had straight plugs. That is the difference. Mine plugs are angled kind of down and in.
My current plugs have threads 3/8" (0.375") long. I believe that there is a 3/8" taper seat plug available.

If you by any chance have a photo of the spark plug hole in your head I'd love to see it. Thanks!!
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Old 08-10-2013, 07:38 AM
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Let me give this a shot at uploading a photo..

[IMG][/IMG]

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Old 08-10-2013, 09:19 AM
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Quote:
Originally Posted by joyridin' View Post
Let me give this a shot at uploading a photo..

[IMG][/IMG]

Thank you for the photos. Enlightening! If you're using tapered seat plugs in these holes, I'm inclined to believe that my heads will work fine with them if I'm able to find 3/8" reach plugs. Now to further my search and find a tapered seat peanut or shorty style in the correct heat range with a 5/8" hex.
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