Hi,

I'm no expert by any measure, and have had no issue with red blocks, but I can recall 3 experiences with definite rod knocks.

The first 2, a 50 IHC and a 55 Chevrolet developed the knock while driving and neither made it home under their own steam. Both sent the rod through the block in under 10 miles.

The third was a 62 Rambler with a flat head Continental. This also developed suddenly but I was able to somehow baby it 50 miles home, holding my breath the whole way. The knocks were pronounced at idle and never diminished with warm up. At higher revs they turned into more of a roar.

I have a recent experience that is not exactly as you describe, but similar enough that I thought I'd throw it out there.

I bought a 90 245 this spring that had sat 7 or 8 years in a garage without being started. I got it going and made it home, but it ran so poorly and had noise coming from so many places it was hard to know what I had.

I eventually sorted everything out until all that remained was a knock at cold idle. It quieted down after warm up or higher revs, but wouldn't completely go away. With the hood up and jerking the throttle at idle it sounded exactly what I remembered of rod knock. When I pulled either the plug wire or injector connector on #1 the knock completely disappeared, so I was expecting the worst.

I've heard of piston slap, but I wouldn't know it if I heard it. Searching the brick board on that, somebody mentioned the exhaust manifold gasket and I thought it was worth a look, but I was doubtful. I've replaced several but none ever produced anything vaguely similar to what I was hearing.

Sure enough, when I put my fingers under the #1 exhaust port with engine cold and idling I felt something. I pulled the manifold to find a tiny crack in the gasket and replacing it was all it took to reclaim my $400. investment.

Peter