My 400 engine started making a "clanging" going down the freeway, steady cruise, and it was rather loud, then the noise quit being so obnoxious, but I could hear a clanging at certain RPM's and felt something wasn't quite right.

I limped it home.

Compression check on all cylinders was between 125 and 150, except for cylinder number 7.

I started the autopsy this evening:

I pulled the valve cover to the left cylinder bank, revealing BOTH pushrods bent on the number 7 cylinder.

What could have caused this, and shold I jsut put two new pushrods in and "see what happens" or should I pull the head to inspect the piston top / valves for damage in case the pistons collided with teh valves (or can that happen on these engines?)

Thanks, guys!

Shane

My build is the following:

Ford 351M-400 (400 original cubic inches / 6.6 liters) bored out .030 over to make 408 cubes / 6.7 liters.
Edelbrock #2171 Intake Manifold
Edelbrock Performer #1405 600 CFM Carb
Edelbrock #8844 water pump
Edelbrock Performer-Plus #2172 camshaft and lifters.
Aussie Cleveland 302C "Quench" heads
Pistons: Federal Mogul 427P / Sterling STL-427P30 (same thing) 4.030 diameter, 10CC dish

 

Now thats a nice setup you have there!
Any astimate on the performance of the engine?

as far as the pushrods:
I'd check and see if you can push the valves down or not, so if they're stuck or not.
If not possible, i'd take the head off...
what rockers do you have?

 

OEM rockers. Maybe this is a good excuse to upgrade to some roller rockers and beefy pushrods, huh? What are those roller-rockers guys use?

I discovered it is down on coolant a bit (a half gallon) as well?

How about this theory:

Overheat while my wife was driving causes a blown head gasket. coolant leak while parked seeps into #7. Engine starts up and hydrolock-bends pushrods on number seven - and then punches out more head gasket to ventilate into atmosphere (I can hear what sounds like air leak adjacent to number 7 while engine is running).

I am going to pull the head tomorrow and we shall see about the head gasket - and I want to get an inspection of the #7 piston top anyway.

If that is what the problem was (hydrolock) do I need to pull the oil pan and check the #7 connecting rod or am I totally out to planet X with my whole theory?

 

Seeing as there are no push rods on that cylinder now. I'd try airing up that cylinder and see what happens first.

 

I went ahead and replaced both lifters, both pushrods, and both rocker arms on the number seven cylinder.

She runs great again.

I still do not know what caused the problem, but it is solved now.

A plus is that I re-sealed my intake manifold valley pan gasket (with a new one, of course) and a ton of gaskacinch and silicone so I no longer have an oil leak at the rear of the manifold.