rattle from engine under higher load.

[jcskokos]

I have the 383 2bbl w/727 in my Coronet.

I can drive around all day and not hear this sound, but once I hit some hills or heavy acceleration I have a loud rattle sound coming from the engine area, another way to describe it may be a metallic version of when you are drinking though a straw and have hit the bottom of the cup. I recently replaced the motor mounts to kill another sound, and the tranny mount for a bad shock when going into gear. I rebuilt the carburetor and made sure to get the gasket for the air cleaner to carb because that was where I thought the sound might be coming from. The car has fresh oil, good clean gas. has anyone experienced this or something like it and knows how to fix it?

 

[ga66mopar]

I had something like that happen one time and the torque convertor bolts had backed off. It caused a slight rattle under load.

 

[Ralph Cali]

I had something like that happen one time and the torque convertor bolts had backed off. It caused a slight rattle under load.

Had this problem with my 383 and it turned out to be timing. Check your timing and experiment with it and see if it corrects.

Ralph

 

[hunt2elk]

Sounds like the timing might be advanced to much.

 

[super-bee_ski]

I had this issue on a 67 GTO
1. Timing
2. Could it be a lifter?
But yeah, pre-detonation AND it damamges the connecting rod bearings if left unchecked.

 

[RustyRatRod]

Is this something that's just recently started? If it's a high mileage engine, it could be carbon buildup in the combustion chambers.

 

[jcskokos]

It could be timing, I checked it before, but didnt have the spec on hand so I just put it where the idle felt smooth. I think it was advanced a bit if I remember right.
as for the high mileage part, it just rolled over. I have had the car for the last 6000 miles, and have changed the oils and filters already. I will also check the torque converter bolts when I can get it on a lift at work when I have a slow day.
Thank you.

 

[scotts74birds]

I agree with others on checking the timing. Depending on the year and CR of your motor, you may even have to go below the factory setting to account for today's crappy gas. Or try a tank of premium, and see what happens.

 

[jcskokos]

I found a chart that, if I am reading it right, the timing should be 0*TDC. Can anyone confirm this? I will try to locate the sheet.

 

[hunt2elk]

I don't think you can go by the charts with the differences in the gas from 40 years ago to today. Where is your timing set and are you sure the noise is pre detonation? Are you running premium fuel?

 

[jcskokos]

I am running regular 87 from the pump. I have usually ran arco because I heard they use less additives and other fun stuff, but I was told to try the Mobil station down the street with the same problem. That being said, I am not sure what the sound is, just from what others have had experience with my description of the sound. When my tank empties out(around this weekend) I will try filling with a higher grade. premium around where I am is 91octane.

 

[2059]

from your initial description, It's detination. higher octane will help but tuning the engine to the octane you want to use is the better solution. Keep in mind all the above mentioned contribute to the detination condition, carbon build up ect...

 

[Bruzilla]

I think 2059 hit it on the head. What you're probably hearing is pre-ignition detonation aka pinging. It occurs under heavy acceleration or loading of the engine, especially as temperatures get warmer. What's happening is heat and pressure is causing the air/fuel mixture to detonate before the spark plug fires, which screws up the timing of the engine and can seriously damage your rotating components.

Adjusting your timing can help with this problem, but then you run into other issues by not using optimal timing settings. If your timing is correctly set and detonation is still occurring, you need to increase the octane level of the fuel you're using. The higher the octane level, the higher the pressures and temps have to be to cause detonation. Get your timing checked, then try the next higher octane level of fuel and see if that stops it. If it's less but still there, go to the next level.

 

[RustyRatRod]

Pre ignition and detonation are TWO distinctly different situations people often confuse. Rather than try to explain in my convoluted way, here is a good article on it.

http://www.misterfixit.com/deton.htm

Also, a very cheap and easy way to tell if it's carbon buildup. Take a coke can full of water and slowly dribble it through the carburetor while holding the engine RPM about 2000. This will instantly steam the combustion chambers and break up and carbon that may be there. Carbon buildup does two things. It raises compression, but it also gets hot. So hot that it ignites the fuel and air mixture before the spark plug. THIS is pre ignition. Detonation is something entirely different. Read the link and you will understand.

 

[krowbar]

What year is the 383? You know they made leaded gas way back when.

 

[Richard Cranium]

Sure sounds like you have to

http://biwook.net/gallery/funny-****/really-weird-people/retard-monkey-mouth.jpg

the timing.

 

[RustyRatRod]

ewwwww

 

[jcskokos]

checked timing and it was showing at 30btdc, however when I adjusted it down it began backfiring through the carb and had a severe lack of power. put it back to 25-30(plenty of power and throttle response) and poured some octane booster in the half tank of 87 I had in there and it seemed to reduce it a lot. I have a hill nearby for my test drives and before if I tried maintaining 45mph up the hill it would ping and lose speed at the throttle level to not ping, after the bottle of booster I can hold it at 50 with no problems. I will try a tank full of plus(89) this weekend and see if it is enough, or if I have to pop for the 91.

I will also try the steam thing tomorrow after work. Do I pour in the whole can(slowly, of course), or just a small part of it?

 

[RustyRatRod]

All of it. But slowly. You'll get the hang o fit.

 

[D575]

I had a problem similar to that, it was too much total timing .