High Milage '79 SC "Common Problem"
 

My 225K mile SC has a thing that I am told is common for high milage SCs but unknown what causes:

At around 4000-4500 RPM, during aggresive acceleration, I get a sound like a fast pre-detination with mild amount of black smoke. It usullay happens in lower gears but has been doing it some in 3rd and 4th gear also. It will stop by backing off the throttle slightly.

Anyone have this experience? Any known causes/remedies?

Oh oh. Sounds like broken cylinder studs.

That was my first thought but local independant says they have seen it many times on high milage SCs and it was not the studs.

I suspected maybe the distributor advance was not working properly or mabey the oil scavenge pump was backing up.....

Don't know about the "black smoke" part of this, but I'd remove the valve covers and check all 24 head stud nuts. You may even find part of a broken stud falls right out on the floor from the exhaust side (the usual place for failure).

How do I know this?
My motor is apart right now for this very reason, and your symptoms (except the black smoke) are exactly as mine.

Further to this......

Try *retarding* the ignition timing to around 0 degrees BTDC, and then take a spirited drive. If the noise is gone, I would bet the farm on a broken head stud (or six).

carbon

Mine rattled and smoked too, until the timing was cut a degree or two. flies to redline fine now. All studs were verified as good when John Walker took it apart for clutch and tranny.

It was a huge weight off my shoulders.

rjp

Thanks for the responses. I will check the studs and try the timing thing this weekend and post results.

DLG