River 3.5 v8 no compression in #5

Hi all

Wonder if someone can give me a bit of advice re: my Rover 3.5 v8 fitted to a Series 2.

Bit of background, the block was from an early range rover, I had it rebuilt (rebored, full Rimmer rebuild kit) by a friend about 6 years ago.

I originally had twin carbs fitted but had terrible problems getting it to start in cold so fitted an Edelbrock carb. Its always used too much oil and would puff a little blue smoke on start up when hot. No noticeable blue smoke when driving or overrun.

I’m now rebuilding the landy and so decided to look at the engine. Just completed a compression test (on a cold engine, as everything is stripped off the vehicle, with carb off so WOT). I’m getting 135-150 across all cylinders except #5. No compression registering on the gauge. With my finger over the spark plug hole I only feel faint pressure. I put 5ml of oil in the chamber and retested, again no compression registering on the gauge.

I’ve pulled the head and as per photos there is significant carbon build up on #5 piston on the inlet side. The chambers across the head look very black.

Grateful for thoughts on what to do next. Before I pulled the head I checked the valves were opening ok, couldn’t see and noticeable sticking in the valves and cam lobes seem ok. As I added oil and rechecked (with still no compression doesn’t this points to heads? but nothing obvious I can see.

I figured I should probably remove the piston and check the rings? I did wonder if I had glazed the bores but the other chambers have compression and figured if that was the case all would be low?

Put the plugs back in & with the head upside down (as in your pic) put water or other liquid in the cavity so the valves are covered. Use an airline to blow air into the appropriate leg of the inlet & the exhaust & see if there is a lot of bubbling around the valve.
Check the head is flat. This is best done by an engine reconditioner & yours looks like it need a good clean, possibly slight warpage.
They should also be able to check the head for any cracking.
You have a composite head gasket as opposed to the more usual plain thin steel gasket.
Composite gaskets aren't a bad thing - I used Elrings on my 3.5EFi when I overhauled the heads a few years ago after having both checked. Both had very slight warpage & needed a very light reface. Some comment about they will lower the compression slightly but as far as my RRC is concerned I've noticed no loss - I did fit a new cam/followers/timing chain - but it's got the aerodynamics of a garden shed anyway.
But has a previous owner tried to deal with a warped head by using one?

The other pistons look very clean - have you been having cooling or coolant loss issues? If coolant is getting into a cylinder(s) it can steam clean the piston(s) & is often a good indicator on the P38.

Your head is very black & I wonder if you're running very rich and/or burning oil.
Be worth dropping the sump & removing that piston to check the rings are present & in good condition. If only to rule them out. Will also make checking bore wear easier

Those pistons look way too clean. Given the head is black is be checking the cam is operating both valves properly on that cylinder

Closer look & the exhaust valve your screwdriver is pointing at has what looks like a semi-circular mark on it. Is this just a mark or is it damaged?
Pull both valves & check the seats & valves to ensure they aren't damaged, that they mate properly & that there isn't a build up of carbon on the exhaust valve stem stopping it fully closing.
After cleaning valve & seat use grinding paste & one of the rubber sucker sticks to see how well - or not - the valve seals against the seat.

As you're completing a full rebuild why not just fully rebuild the engine too? Do the job properly and have total peace of mind. If not able to rebuild yourself send the engine complete to Turner's and be done with it. If still on SU's you could rebuild these and set up yourself...or send off to Burlen Fuels down the road from you in Salisbury, they come back better than new.