Clein15

Recently i noticed that my 66 coupe has developed an annoying little rattle when i accelerate. It is a 200 CI straight 6 with a C4 automatic transmission. The engine was overhauled 4 months ago, the transmission was overhauled in 1989 before being put in storage, the exhaust system however, is the original 1966 system. The rattle only occurs when the car is in gear and i am accelerating, i can let off the gas and the rattle will disappear. The rattle sounds like its coming from the firewall/transmission tunnel area. Any help would be great!

Clein15

I'd also like to add that I've been running it off of regular unleaded gas and putting a lead additive in. Should I up it to a higher octane? The oil does need changed soon so I'm going to check the exact mileage later to see if that's a possible solution

Diputado

Put the car on a lift and check for anything loose along the exhaust system. If that is the original exhaust...something may be rusted out or loose.

JAGGUY

I have had the starter drive contact the flywheel on mine and have read others have the same problem.
Replaced starter and noise was gone.

Clein15

Checked the exhaust out, there is nothing loose however it is rusted terribly. The starter is old as well so I'll pull that out and have a look. I'm going to have someone come down and trouble shoot it this week with me. Thank you for the help so far guys

jlg2002

Typically, rattling on acceleration is caused by octane vs ignition timing issues. essentially too much timing advance for the octane in the fuel. try going up to premium for a couple of tanks. and double check your dwell and timing are at spec.

You may also have combustion chamber carbon deposits that are flash starting the air fuel mixture. An old mechanics trick i learned back in the 70's was to take a pop bottle full of water and slowly pour it down the carb while at high idle. With the idea that the steam generated in the combustion chamber cleaned the carbon out- i'm not sure if this is true but it seemed to work back then.

Clein15

Well that start went on me tonight so i think it was that but im still going to run premium for a few tanks and ill run a bottle of water through after we replace the starter as well. Thanks guys!

Clein15

Fixed the errors... err not having a good night -.-

jonward786

I had two occasions of rattling. First time muffler was too close to floor and it was lightly banging against the car. Second time the rubber in the transmission mount was completely cracked and the transmission was bouncing off the tunnel

Diputado

I agee with all the recommendations EXCEPT pouring water down the carb. Doesn't sound like a very good idea to mix oil, gas, AND water in the upper cylinder/combustion chamber. Interestingly though...my Dad used to use a similar type of trick to "clean the valves"...but instead of water he used automatic transmission fluid. I watched him do it, and he would run the engine at a fast idle (about 1200-1500 rpm) and very slowly trickle about a couple ounces of fluid into the carb. The engine smoked like hell for a couple minutes, but ran just fine afterwards. Safer and easier on the upper cylinder walls than water. Just keep the rpm up...if you let it go dead while doing this, you'll have to pull the plugs and clean them to get her started again.