Mystery tap

[724xz]

Alright got a 85 720 2.4z blew head gasket between 3 & 4 replaced it along with the pesky tensioner deal got everything back together and adjusted valves cranked and there is a constant tapping noise coming from the same area.  also before start I went through the bottom end main bearing caps before accepting the headgasket failure, any ideas, valve sticking, piston failure from cam timing? Sounds about the same as when it blew less the miss. 

[datzenmike]

From what you say, it sounds like it was tapping before you blew the headgasket? Yes?

 

Unlikely a piston or you would have seen damage when changing the gasket.

 

Main bearings rarely go bad as they get oil first before feeding the rods. All the mains do is turn and there's 5 of them to share the load. Rods are all alone taking the pounding from the piston.

 

 

Knock? A lower frequency like a 4 pound sledge hammering on the block?

Does it get louder if you step on the gas briefly? Yes.... Rod bearing.

 

Taps are higher pitch and metallic. Ticking. Has to be in the top end. Valve lash is 0.012" on both. Set on a hot not cold engine.

 

 

[DIY 1985]

But it doesn't sound like a ball bearing hitting the bottom of a paint can?

[Stoffregen Motorsports]

Does it run better since you replaced the head gasket? I have seen erosion in the aluminum between combustion chambers. This can cause a "tap" almost like an exhaust leak.

 

Are you sure you don't have an exhaust leak? Like a cracked manifold? That can sound like a tap.

[datzenmike]

Again it would get louder under load.