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Unread 08-19-2005, 10:40 AM   #1
JerseyDevil541
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Valve Rattle

Hey Folks I hope you can help.
I have a 1982 CJ-8 with a rebuilt 4.2 (22 K miles) using a Holley 7448 carb and an auto trans.
The valves sound like i'm making POPCORN when I get on the highway and pull a hill.
The timing is set at 5 degrees (it was WORSE set at 6).
I've added the "Juice Box" upgrade (big distributor cap and 8mm wires and big output coil).

Is there a test you can recommend to make sure the HEAD isn't messed up ?
Any ideas or suspicions ???

I'm worried that if I keep driving it the way it is.... something will go BANG !

Thanks
Charlie

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Unread 08-19-2005, 09:00 PM   #2
78jeeper258
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Sounds like you are suffering from predetination or knock. Todays 87 octane usually sucks for older vehicles. Some 87 octane barely seems to burn in my CJ but that can stem from a contaminated tank at the gas station.

Try switching to a higher grade of fuel (93 octane) or dumping some octane booster from an auto parts store to see if your problem goes away.

Not sure what stock timing is on that motor but try slight variations since it is likely that might help matters.

Just wondering what plugs you are running and when they have last been changed.

To answer your last question, if it is knock, then it will potentially hurt the motor.
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Unread 08-20-2005, 06:03 AM   #3
JerseyDevil541
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Thanks for your reply

I'm using Bosch Platinum.

I'll try the octane boost to see if it helps and try using SUPER gas next week.
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Unread 08-20-2005, 05:47 PM   #4
78jeeper258
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About those platinums

Just a point of interest, in my experience, those Bosch Platinums really suck. I have had 3 cars, a ford escort, a chevy s-10, and a dodge shadow not run correctly after the owners had me put Bosch platinums in. A set of AC Delco plugs may be what you are looking for to fix your problem.

With current fuel costs, your fill-up next week may cost the same as a set of new plugs.

Last edited by 78jeeper258; 08-20-2005 at 05:48 PM.. Reason: typo
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Unread 08-21-2005, 11:27 PM   #5
Fullsize_CJ5
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sounds like pre-ignition to me. The fuel is igniting as soon as the piston starts up on it's compression stroke, this causes the piston to "rattle" in the cylinder. It's sounds terrible but doesn't usually harm your engine. Make sure your engine timing is set correctly, also be sure the engine is not running hotter than it should. Higher octane fuel will most likely stop the problem.
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Unread 08-31-2005, 12:07 AM   #6
Jerry Bransford
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Quote:
Originally Posted by JerseyDevil541
Thanks for your reply

I'm using Bosch Platinum.

I'll try the octane boost to see if it helps and try using SUPER gas next week.
Could your engine be loaded up with carbon in the combustion chambers? Carbon is a common cause of premature ignition/pinging/detonation.

I agree on the recommendation to get rid of the Bosch Platinums, they don't normally work well in Jeep engines. And if they're not the right heat range, they could even cause or contribute significantly to the pinging. And a properly running 4.2L engine definitely (!) should not need any octane higher than 87 to run properly. I'd find the real root cause of the pinging and not continue to waste more money burning the wrong octane.
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Unread 08-31-2005, 11:19 AM   #7
Vinnyl32
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Quote:
Originally Posted by Fullsize_CJ5
sounds like pre-ignition to me. The fuel is igniting as soon as the piston starts up on it's compression stroke, this causes the piston to "rattle" in the cylinder. It's sounds terrible but doesn't usually harm your engine. Make sure your engine timing is set correctly, also be sure the engine is not running hotter than it should. Higher octane fuel will most likely stop the problem.
"Dosent usally harm your cylinder" Yea right Pre-ignition (pinging) is caused by high combustion chamber temps. If you continue to drive your engine with pre-ignition temps can get so extreme that you could melt the piston, damage the cylinder etc. I have seen it happen....
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