Mailbag: What’s Poppin’? Possibly Worn Cam Lobes

Got questions?
We’ve got the answers—Mondays when the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re diagnosing unwelcome exhaust noise.

From: R.C. • Dunnellon, FL
Q: I’m having a problem with my 1979 Monte Carlo/406 project that I can’t figure out. I’ve driven the car for about 5,000 miles, and it’s developed a popping noise through the exhaust. The noise is not very loud but it happens in one-second gaps at 800-1,000 rpm. Before this problem, I changed the thermostat from 160 degrees to 190 degrees because it was taking too long to reach operating temperature. However, now it reaches over 200 degrees when idling! Any help would be greatly appreciated.

A: Sounds like your camshaft has a lobe or two going flat. It’s common wear and tear in older engines like yours. When an exhaust lobe begins to flatten, it will develop that popping sound and run warmer than usual. To diagnose a flat lobe, simply remove your valve covers, turn the motor over by hand, and check if all of the rockers are moving the same. You’ll most likely find one or two moving out of sync because of the lobe flattening. To get your Monte Carlo back in ship shape, you’ll likely need to swap out that old cam with something new.

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