Classic/Antique Car Repair/1978 Chevy 350

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Expert: - 12/20/2007


Question
QUESTION: After my car warms up, I hear a loud knocking. I did a tune up on it... plugs, plug wires, oil & filter, (didn't change the cap) & it still knocks. Could it be the wrong plugs that were installed? Could it be timing?
It runs good & never backfires or stalls! It never knocks when I first start it... only after it's warm! Please Help!
Thank You

ANSWER: Hi Dave:
When you say knocking, do you mean tapping, like the rods or lifters tapping? Or is it a clunking sound coming from underneath the car? If the latter, is your Chevy a manual shift or automatic? It could be the clutch if manual shift. Answers to the above questions will help nail the problem down.

---------- FOLLOW-UP ----------

QUESTION: Sorry! It's an automatic. It's not a clunking sound, more like a loud tapping. I only hear it, when I'm at an idle. (stop light & pulling unto garage.) When I pop the hood, I can't pinpoint the location of the noise.
Thanks

Answer
In that case, the problem sounds like your valve lifters or rockers. Take the oil cap off and listen closer inside the heads and see if this is the case. Normally sufficient oil in the motor can quiet them if they are not worn too badly. Check the oil level (when car is cold, not running). If oil is full and clean, I suggest (as a temp fix) you add one quart of Lucas Engine stop leak. Otherwise, it may be time to rebuild the engine. Does it smoke any when pressing the gas?

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Visit my website at: http://www.classytransportation.com/ I can answer most questions about autos built in the 60's 70's and 80's. Specifically, Lincolns, Rolls Royces and the Excaliburs. Mechanical issues and technical questions are my expertise. I also have a general knowledge of most older automobiles. Keep in mind, I can only provide answers if the questions are very specific and complete. Without details, I can only speculate and that's not good for solving your problem.

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