rattle on acceleration

[William F.]

Just had the plugs changed on my '67 L79 (Denso 14P-U's) because of a high rpm miss. Pulls to redline now but around 4500-5000 rpm, sometimes lower, I hear a loud rattle, not a "ping", sounding like it's coming from right side of dash or right side of engine compartment. Not sure if I heard this prior to plug change or not. Timing set to 10 degrees BTDC, using non ethanol 93 octane Shell. Added about 1/4 tank of 110 racing fuel and still same rattle. Wouldn't seem to be detonation unless a hot spot in one of the cylinders. Know this is a tough question, but what do you think?-loose spark plug?, hopefully just something under dash, but what?
Thanks

[Gene M.]

Re: rattle on acceleration

If you just changed the plugs then check there first. Could be loose wing nuts on ignition shields or loose plug heat shields. Were all the plug compression washers in place when installing new plugs?

[Joe C.]

Re: rattle on acceleration

Does the car have factory sidepipes? If so, the inner perforated tube could be rattling. It could also be the inspection cover on the bellhousing.

[William F.]

Re: rattle on acceleration

Thanks,
Yes, it has side pipes. Could the chrome strip covering the top of the side pipe shield also be a source of the rattling?

[Joe C.]

Re: rattle on acceleration

Thanks,
Yes, it has side pipes. Could the chrome strip covering the top of the side pipe shield also be a source of the rattling?

Not likely if it's installed correctly. There should be a steel retainer strip that runs along the door sill and which locks the entire upper edge of the spear molding tightly in place. The original sidepipe mufflers' inner perforated tubes are made of thin sheet metal. Mine drove me crazy and almost sounded like detonation. After I replaced them with very low restriction mufflers, the rattle was gone.

[William F.]

Re: rattle on acceleration

Joe,
I can rattle the passenger side "spear(I'm calling the "spear" the chrome and black painted strip that runs front to back at top of side pipe shield)by hand, but not sure if this is what's rattling while I drive. Guess I'll have to get a knowledgeable friend ride shotgun with window down and see what he hears.

[Joe C.]

Re: rattle on acceleration

Joe,
I can rattle the passenger side "spear(I'm calling the "spear" the chrome and black painted strip that runs front to back at top of side pipe shield)by hand, but not sure if this is what's rattling while I drive. Guess I'll have to get a knowledgeable friend ride shotgun with window down and see what he hears.

Take that one off and drive it to check. You'll also verify the presence of the retainer strip at that time. Easier to attach "spears" without the retainer and sometimes these are omitted. It's more likely that the rattle is coming from inside the muffler.