Td42 zero compression in one cylinder

hi, I have a td42 that was running on 5 cylinders. I took it to my mechanic who told me it was down on compression on some cylinders and the number 3 cylinder had zero compression. I have pulled the cylinder hoping to see the cause of said lack of compression but I can see anything wrong, is there anything in particular I should be looking for. I was hoping to have found a stuck valve but that doesn't seem to be the case. Any help will be much appreciated

Since it's down on other cylinders as well as the 'zero' one, you can expect the problem to be more than just a sticking valve.

You could do a cylinder leakage test, or make up an adaptor to replace the injectors that you can connect an air-line to and see where the leakage is going by bringing it to TDC on firing (one revolution from overlap) - if into the exhaust you'll hear it there, same with the intake at the manifold intake. If it's past the rings you can hear it from the filler cap, into the cooling system there will be bubbling at the filler.

After doing some checking, seems that engine is very susceptible to cracking the head if overheated, which may be the problem.

Regardless, eventually you're going to have to pull the head to check several of the components that may be contributing to the problem.

Unfortunately I have jumped the gun and removed the cylinder head, I'm thinking I might fill the intake and exhaust runners with fluid and see if they leak, I have already filled the suspect cylinders intake runner with WD40 and I can see it leaking, albeit very slowly but I'm unsure if WD40 is too thing for this test and if so what fluid I should use. I will also add that this is a push rod engine so no valves should be opening. Thanks again.

A leak is a leak - more viscous (thicker) fluid will just slow it down.

However, that may not matter, anyway - there is a mark that looks a LOT like a crack at the 8-9 o'clock position of the intake valve seat pictured (and you doubled up again), running towards the exhaust. What are the others like?

Clean the head surface and have a good look and any crack should be very obvious.

What do the pistons and bores look like?

So I've given it a bit of a clean with some break cleaner and a rag, thinking I might hit it with a toothbrush tomorrow, I haven't found any cracks in the head, but it looks like most of the pre combustion chambers have cracks in them. I wonder if this could lead to lower compression.

Maybe a helpful tip for u. I found the best way to test valves is to fill the combustion side of the head with water and blast compressed air through the runners, valves should be air tight

I don't expect so, but it isn't a good sign and if they aren't servicable parts, might mean the head needs replacing - you really need to take it to a head specialist for cleaning, checking and an accurate assessment of the head's condition.

Those other cylinders look OK, it was that first picture that hasd what appears to be a crak from the valve seat.

Are you able to identify which picture goes with the good, weak and no compression test results?

Have you had the piston and bore condition looked over yet?

Yeah the precombustion chambers can be purchased new and installed, I have filled the intake ports on the head with methylated spirits and every single one leaked, some more than others. I will be taking it to cylinder head shop but its the long weekend and I was hoping to some stuff done on the car. I haven't had a good look at the cylinders but when I removed the head I turned it over and couldn't see any damage.

Also the photos are labelled to the corresponding cylinder number 3 is the cylinder with zero compression.

Ah, me bad... hard to make out, since it's been cleaned up, if it really was cracked or a casting irregulaity.