I have a 1974 F-250 with a 390 and supposedly 428 heads. I have a ticking sound which sounds like an exhaust leak from the number 4 and 6 cylinders. When I pull the spark plug wire off while it is running the sound goes away. That would be a rod knock, correct? The noise is only at idle and acceleration. If I hold the RPM at 1200 or higher the sound is not there. A rod knock is always present isn't it?

Compression checks out good. Oil pressure is 3/4 up the stock gauge. Sound doesn't change at all depending on engine temp. I put in a quart of Rislone but it did nothing. When I bought the truck the two problem cylinders also had the exhaust manifold gasket blown out around the exhaust ports, not sure if that is related.

I've seen on this forum about the wrist pin making noise. What causes that?

Where should I start?

 

I'd install a mechanical gauge to get some numbers with your oil pressure. Have you changed the oil recently? How did it look?

 

[quote=1974f250;6997446]

When I bought the truck the two problem cylinders also had the exhaust manifold gasket blown out around the exhaust ports, not sure if that is related. quote]
Did you replace the gaskets? Pulling the plug wires would quiet a leak. A rod knock sounds like just that, a knock not a tick.

 

I changed the oil about 800 miles ago. It looked dark but no metal. I haven't owned the truck very long so now telling how many miles were on the oil. I will hook up my mechanical gauge tomorrow.

Yes, I changed the exhaust manifold gaskets and they are not leaking.

 

Oil pressure at idle is 60psi cold and 15psi warm. At 2000 RPM warm it is 40psi.

 

I pulled some rod and main bearings. They are both a little into the copper. I heard it's possible to change main bearings without dropping the crank. Is there a special technique to this? If I unbolt all the caps will I get enough play in the crank to slip the upper bearing around?