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pulled threads out of carb
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sat Jun 08, 2013 11:34 pm    Post subject: pulled threads out of carb Reply with quote

went out for a little T&T friday night at the local 1/8 mile track. car is still lean but getting better. my third pass i made nearly a full pass before afr started getting north of 13:1. this was the longest run under boost at WOT. it popped and started running a little weird. i thought i hurt it but it cleared out by the time i made it back down the return road. i jetted it as fat as i could with what i had in my tool box and went for another pass. immediately after launch, the bonnet popped up and this is what i found....





i really dont know what boost was. i was buisy watching afr Embarassed . so, im thinking about a helicoil and permanently epoxying that and the stud into the carb. before i do that, does anyone have a better idea ?

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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Sun Jun 09, 2013 12:43 am    Post subject: Reply with quote

Can you add more fasteners?
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Skunkworkx
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1968 Chevrolet Camaro

PostPosted: Sun Jun 09, 2013 8:20 am    Post subject: Reply with quote

Where does the stud go ?

Pinning may be an option also ?

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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sun Jun 09, 2013 11:04 am    Post subject: Reply with quote

sorry, i forgot to mention that this is the stud for the bonnet.

i was also thinking about building something off of the four carb bolts that hold it to the intake. i just havent come up with any decent ideas on that yet. lots of issues with linkage.

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clay
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1972 Chevrolet Nova

PostPosted: Sun Jun 09, 2013 11:07 am    Post subject: Reply with quote

If it is still using the 1/4" thread, I would drill and tap it for a 5/16" - 18 all the way through. I use a piece of threaded rod and run it down as far as possible in the carb and use a locknut to keep it there. It doesn't look like you had a lot of thread engagement and I'm thinking that was your problem. If you do the math on a 5 1/8" area at 20 lbs. boost you're looking at just over 400 lbs. trying to blow the bonnet off. Wait till you blow a hose off - that makes a pretty good bang Laughing . Clay
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af2
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1933 Willys Coupe

PostPosted: Sun Jun 09, 2013 5:50 pm    Post subject: Reply with quote

That looks like it goes in the base plate. I would time sert it with loktite then thread a 5/16 rod as Clay said.
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af2
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1933 Willys Coupe

PostPosted: Sun Jun 09, 2013 5:52 pm    Post subject: Reply with quote

Still wondering why more bonnets don't exit the hood on a good back fire????
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clay
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1972 Chevrolet Nova

PostPosted: Sun Jun 09, 2013 7:33 pm    Post subject: Reply with quote

That's a good question. My first time at a 1/4 mile track I hit the rev limiter right at the stripe and for some reason it backfired bigtime. It blew off a 4" hose on the inlet of the supercharger. It took out the thrust bearing in it but the bonnet was fine. Go figure. Clay
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Sun Jun 09, 2013 11:42 pm    Post subject: Reply with quote

Clay, what are you using for a gasket to seal the bonnet to the carb ? im just using a plain old paper air cleaner gasket. if the bonnet isnt really tight, it blows the gasket out. im thinking that, having to tighten it down so much may also be an issue with the threads pulling out.
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Paul P
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PostPosted: Mon Jun 10, 2013 1:10 pm    Post subject: Reply with quote

Use a heli-coil and grade 8 1/4-20 stud. A jam nut or a long hex standoff is a good idea to stabilize it.
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af2
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1933 Willys Coupe

PostPosted: Mon Jun 10, 2013 5:34 pm    Post subject: Reply with quote

10sec.et wrote:
Clay, what are you using for a gasket to seal the bonnet to the carb ? im just using a plain old paper air cleaner gasket. if the bonnet isnt really tight, it blows the gasket out. im thinking that, having to tighten it down so much may also be an issue with the threads pulling out.


Keith, on the 6-71 deal we use two receivers with .030"x '.125 groove and a band of o-ring at .125" to seal at 25 lbs. They only fail on a big backfire but then the burst panel and the fire wall have been reshaped.... Embarassed
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clay
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1972 Chevrolet Nova

PostPosted: Mon Jun 10, 2013 7:47 pm    Post subject: Reply with quote

I've got you some gaskets on the way - should be there Thursday. Extreme Velocity uses an o-ring between the bonnet and their spacer if you run one. Usually the bonnet itself isn't thick enough to cut an o-ring groove in the face and you can't put one on most carbs and use a chamfer on the bonnet because there are open areas on the carburetor that won't support the o-ring on the i.d. like their spacer does. The o-ring just seals bonnet to spacer - you still have the same problem under the spacer. I made some plastic rings that basically serve to protect the carb and bonnet rubbing together. I have used nylon but for some reason it gets larger over time. I don't know if it is due to heat and pressure or it's a reaction to gasoline vapors. I believe the one's you're getting are made out of delrin - I made them a year or two ago so I'm not sure but that's what the material looks like to me. It doesn't conform much at all but it really doesn't have to be sealed 100% airtight - there are so many cfm going through the system you'll never see a small leak performancewise. Clay
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10sec.et
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1969 Oldsmobile Cutlass

PostPosted: Tue Jun 11, 2013 1:43 pm    Post subject: Reply with quote

Paul P wrote:
Use a heli-coil and grade 8 1/4-20 stud. A jam nut or a long hex standoff is a good idea to stabilize it.


that was my original thought. the stud already is grade 8. the problem i see is the helicoil is not very long. still wouldnt have much thread engagement. i have tried doubling them up and i can never get them lined up well enough to work.

im probably going to drill and thread all the way to the throttle plate for a 5/16 stud and loctite it in place with a jam nut.




clay wrote:
I've got you some gaskets on the way


awesome !!!! Cool I'm not worthy

i need to give you a call one evening. im thinking about trying the extended vent tubes again.

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clay
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1972 Chevrolet Nova

PostPosted: Tue Jun 11, 2013 7:19 pm    Post subject: Reply with quote

Quote:
im probably going to drill and thread all the way to the throttle plate for a 5/16 stud and loctite it in place with a jam nut.

That's all you need. I would just run a jam nut and forget the Loctite. Keeping the stud tight in the carb is all you need. Stacking helicoils is definately hit and miss. Give me a call whenever. Clay

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William Jones
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1971 Ford Mustang

PostPosted: Tue Jun 11, 2013 8:15 pm    Post subject: Reply with quote

Here is a pic from one of the guys on another site im sure with your skills you will do somthing nicer than this.

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