My car engine sounds like BB's in a coffee can !

Dougsters · Jan 23, 2013

My bone stock 1966 C Code on light acceleration/deceleration 1200-1800RPM range makes a sound like BB's or samll nails in a tumbler from engine/exhaust header area. Background: I removed smog pump a year ago and didnot have the noise. It is timmed to 10 Deg. Int. Total is 32 @ 2500RPM. Vac. Adv. 15 deg. in at 1200. Carb set correct (float level etc.) Plugs reflect good burn. Vac. @ 17". I'm wondering if the extra o2 from smog pump was burning any extra fuel that carried over to exhaust? Live in So. Cal. (Thermactor still on) was on when I bought in 2010,so only removed pump to date. It's not like a backfire but a rattle or small fire crackers. Below and above above RPM range no problem? Any help appreciated as I'm out of ideas. Thanks in Advance.

Hwyman · Jan 23, 2013

After I had to buy a replacement pump once when mine wore out, I started leaving the belt off except when I took it in to smog. When it finally got old enough so I didn't need to smog it, I took the pump off and put plugs in the end of any open hoses. I never had any issues with noise or pinging. Not sure what is causing your problem, but based on my experience, it isn't the missing smog pump.

Dougsters · Jan 23, 2013

Hwyman said:
After I had to buy a replacement pump once when mine wore out, I started leaving the belt off except when I took it in to smog. When it finally got old enough so I didn't need to smog it, I took the pump off and put plugs in the end of any open hoses. I never had any issues with noise or pinging. Not sure what is causing your problem, but based on my experience, it isn't the missing smog pump.

Thanks Hwyman--Maybe it's not related but need to remove Thermactor headers and plug the heads like you. With Thermactor manifolds on the spark plugs are a PITA to change .

madspeed · Jan 23, 2013

you have cats on it?

Dougsters · Jan 23, 2013

madspeed said:
you have cats on it?

No Cats, just stock exhaust manifolds H pipe then oval stock mufflers,reasonators then out the back valance via trumpet GT tips.

woodsnake · Jan 23, 2013

Any chance this is a "buzz" sound? Like an exhaust pipe vibration, from a bad engine mount?

jka · Jan 23, 2013

Have you checked for exhaust leaks?

65ShelbyClone · Jan 24, 2013

A clear video of the sound could be helpful.

madspeed said:
you have cats on it?

On a '66 Mustang?

Mr67Stang · Jan 24, 2013

What fuel are you using? What you describe sounds like it could be predetonation, which can destroy pistons and bearings. If you are using premium fuel (92-93 octane) a stock 289 should be fine. If you are using CheapoEthonol 87 octane then this may be your problem. These cars were built when we had leaded gas at 100+ octane. I have in the past described the sound as someone crinkling up aluminium foil or hard celophane plastic under the hood. It tipically happens only when the engine is under a load such as initial take off from a stop or climbing a hill. Exsessive carbon build up in the combustion chamber and top of pistons can cause predetonation as well. So, if your wondering why you never had the problem before, this is a possability.

65ShelbyClone · Jan 24, 2013

Whenever I see "BBs in a coffee can" mentioned, I immediately think pinging, but it's happening under deceleration too.

Dougsters · Jan 24, 2013

Mr67Stang said:
What fuel are you using? What you describe sounds like it could be predetonation, which can destroy pistons and bearings. If you are using premium fuel (92-93 octane) a stock 289 should be fine. If you are using CheapoEthonol 87 octane then this may be your problem. These cars were built when we had leaded gas at 100+ octane. I have in the past described the sound as someone crinkling up aluminium foil or hard celophane plastic under the hood. It tipically happens only when the engine is under a load such as initial take off from a stop or climbing a hill. Exsessive carbon build up in the combustion chamber and top of pistons can cause predetonation as well. So, if your wondering why you never had the problem before, this is a possability.

I here you with the fuel,previos owner used 89 grade I use 91 octane. I grew up in the sixties so I know this calif. gas is crap now! When egine gets up to temp.,sound is less pronounced. I'ts diffently in the engine I disconnected Vac. Adv. but still does it,thougt it might be advancing to quick. When decelerating I can have my foot off the gas and it still makes sound around 1500 RPM's. This is where my vacuum adv. was all in so tried the above disconnect. Need to get audio file. Thanks all for your help ,will get back with more info. once it stops raining.

65ShelbyClone · Jan 24, 2013

Pinging is unlikely if it happens under engine braking like that.

Hwyman · Jan 24, 2013

It's a little bit of a pain, but---- one by one you could remove a belt and go for a real quick drive. It would eliminate something like a bearing going bad in one of the accessories (alt., water pump, etc.)

jka · Jan 24, 2013

Have you checked or tighten the header bolts? If this noise gets better as the engine is warm.. i would check for exhaust leaks at the header. I had a header leak that was so bad it sounded like my engine was about to come apart ..turns out i blew one of the header gaskets.

bartl · Jan 24, 2013

If you still have the Thermactor tubes on and the hoses aren't plugged you'll get that sound from the anti-backfire valves.

Dougsters · Jan 25, 2013

bartl said:
If you still have the Thermactor tubes on and the hoses aren't plugged you'll get that sound from the anti-backfire valves.

bartl-Thanks for info ,yes I stll have thermactor manifolds on and check valves.Check valves now have a rubber cap and hose clamp where hose would have went. I guess if valve malfunctioned it makes sense. Need to remove one day but they are a PITA so waiting for engine rebuild. Again thanks to all for the help.

Dougsters · Jan 25, 2013

Hwyman said:
It's a little bit of a pain, but---- one by one you could remove a belt and go for a real quick drive. It would eliminate something like a bearing going bad in one of the accessories (alt., water pump, etc.)

Good idea will keep it on my list .TX

madspeed · Jan 27, 2013

65ShelbyClone said:
On a '66 Mustang?

You never know! I've seen and heard it many times where the catalyst inside the converter breaks loose from the housing and rattles like bb's in a can. In this case, thats easily ruled out

My car engine sounds like BB's in a coffee can !

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