I just did a head gasket on bank two of a V6 after it didn't seal the first time but was running fine. After starting and it warmed up the engine I got a misfire codes on all cylinders on bank 2. So I did a compression test, Bank 1 all 140-5 psi and bank 2 all 160-5 psi. I did a leak down test bank 1, 3%, bank 2, 4&5 25% leaking back into the intake and 6 is 5%.
Any ideas before I pull the head off again?

 

Was the engine overheated resulting in the need to replace the head gasket?

 

Yes, but I've rebuild the engine with another used block and had the heads planed, the block look ok. I had the engine going fine but bank 2 head gasket started leaking exhaust gas into the coolant so I took it off and hand planed the bank 2 block. Seem to have fixed the head gasket leak.

 

I'm thinking that the different in pressure readings between bank 1 & bank 2 is because of the different work done on each side. That is B1 has only had a head plan (1 time) and B2 has had the head planed 2 times as far as I know and the block planed 1x. Both sides have .6mm head gaskets but I'm surprised how much that has affected the pressure between the banks.
I'm thinking of changing the head gasket on B2 for a thinker one (1.2mm) and sorting out the valve leaks to try and get the pressure between the two banks closer.
Any thoughts?

 

 

Right hand Cylinder head
I took the head off again, this is what the exhaust valves seats looked like. I'm going to re lap and test them.

 

+1 on relapping the valves as they don't appear to be sealing fully.

Did you inspect the block and heads with a straightedge and measure each at several points?

 

Yes, The block was in spec, just and the head has just been machined and its flat. I need to check the valve lash too. Yes, It looks like the exhaust side is not sealing? I should also check the spring pressure.