TLDR; engine making clacking sound only at acceleration, sounds like exhaust leak at headers to me but shop is telling me cracked piston and to replace the entire engine.
Attached vid is a little long but you can hear it kick in at about 10 seconds, and again around 1:20 mark.
Details: 1971 El Camino with a 1979 Chevy 350 4 bolt main, bored .30 over, recently started clacking when accelerating over 35mph. The clacking only occurs only when accelerating in gear, stops immediately when I take my foot off the gas. Does not make clacking sound while in park and pressing on gas. Other than the noise, there are no other symptoms, drives butter smooth, no smoke, no slop, no vibration, starts 100% and idles great.
Shop is telling me it’s a cracked piston and recommending replacing with a new crate engine. I’ve been using this shop for 12 years but something in my gut just doesn’t feel right about this, it’s a lot of money so I’m really just looking for a sanity check here. I’ve heard a car with piston slapping and it’s constant, even at idle. I feel like a cracked piston would be a constant sound while the engine was running, just seems odd to me that it only makes noise when I’m pressing the accelerator. I’m leaning towards exhaust leak at headers but could be entirely wrong, I am absolutely not a mechanic.
Other possibly relevant details…I’ve dropped over $7,000 into this car in the last 10 weeks.
Replaced:
- Alternator
- Front Wheel Bearing
- Master Cylinder
- Rear Wheel Cylinders
- Throttle Cable
- Radiator
- Driveshaft
- Transmission
After all this, I’m obviously not thrilled at the idea of dropping upwards of $10k for a crate engine and install, I’ll absolutely do it if need be but I really just would like to hear from others if this sounds right, I acknowledge I am not a mechanic in any way shape or form and totally ignorant, and my gut feelings have been wrong before, but that’s a lot of money and thought I’d see if you all had any thoughts before I bother other shops for appointments for a second opinion.
If I should get a second opinion, I’d be greatly appreciative for any shop recommendations in Southern New England