SC engine noise question
 

Here's the information:

- 1981 SC with 93k on the odometer
- spark plugs replaced 1,500 miles ago with regular Bosch
- timing reset by local shop to 5 degrees btdc and centrifigal advance set to 16 degrees at 3k rpms and 24 degrees at 6k rpms less than 400 miles ago
- always have used 93 octane fuel from Exxon

here's the noise and question:

- at about 3800 to 4200 rpms in 2nd gear under constant acceleration there is a slight pinging/knocking noise
- noise is not heard in any other gear or in any other rpm range
- it is not breaking or suspension and once I either let off the accelerator or press it down further the noise stops

ideas or suggestions?

could it be preignition or detonation with the current settings and selected range of occurance?

thanks for the help!

bump

My 83 had the same ping on hard acceleration when I first bought it. A Techron treatment took care of it. Carbon buildup. Could also be a broken head stud or two, but hopefully just carbon. Good luck.

Check your valves, mostly so you can check for broken studs. That's where my money is and why my car is doing the same thing. Take a torque wrench to the studs and make sure there aren't any loose ones.

Dr. Williams: how was dinner?

Thanks for the ideas guys.

Here's another twist to the puzzle:

- it is intermittant and cannot be replicated when stopped and revving the engine up to 5k rpms.

I drove it to work today and only heard it once as I was accelerating hard through 2nd to 3rd. Twice when stopped I stood on the brakes and revved her to 5k, stopping at 4k for a few seconds. Not once did I hear it.

I am begining to think maybe there is something loose in the engine compartment so I will check that possibility.

Keep the ideas coming ...

Get Thee a bottle of Techron.

It only doing it under load is exactly the way it happens. It also doesn't do it hardly at all when the motor is cold. In the morning on the way to work, mine rarely ever does it. In the afternoon or after running for a while and the motor is nice and warm, it will do it much more.

Dr. Static, lets just say her cooking is very comparable to my engine rebuilding. Capable, but needing experience. I told her I'd be happy to remove the batteries from the smoke detectors for a while. :p Good thing I have about five extinguishers at home.

And go figure, the pans don't just wipe clean with a paper towel after burning things like the guy told her. Who knew?

They are pretty nice but OMG. She will be practicing a lot so wish me luck. So far she's 1:1. I told her she can practice all she wants until I either gain or loose a lot of weight, then I'm going back to the cooking.

rstoll- I meant to put this in my last post but forgot: I hear you (about the techron) and will pick one up this week. This is something I've been meaning to do for awhile since I've had the car over a year and don't know when/if it was ever done before.

Head stud(s).

Try this test:
Retard the ignition timing to 0 degrees BTDC or more.
Drive the car, revving to 4-5K rpm while listening for the noise.
If you no longer hear it with the retarded timing, you likely have a broken head stud.