M42 Running on 3 cylinders after head replacement

[JBentley95]

Hi all, please HELP !

I had to remove my head after the chain tensioner boss cracked and required welding back on (previous owner didn't use a crush washer and over tightened the chain tensioner to stop oil leak !).
The engine was running fine before removing the head and under inspection everything looked very clean. I did not mess with the head at all, apart from welding the boss back on and giving it a good clean/paint.
Put everything back together with the timing correct and cranked it over by hand a couple of times to roughly check.
Engine started first time but sounded like a bag of nails with some noticeable misfiring. I thought maybe the hydraulic tappets needed to fill up so I pored a bit more oil in the head and ran it for a bit at 2500 RPM. This didn't solve anything and the misfiring got worse. Also I stupidly didn't keep an eye on my temp gauge and the engine got pretty hot ! (Air lock in the cooling system, which I then sorted out)
Took the valve cover off and turned the engine over using the end of a screw driver to roughly check compression (didn't have a compression tester). The front cylinder had almost no compression. I cranked it over to dead center leaving all valves closed on the front cylinder. Using a bit of pipe to fit I blew into the cylinder and could feel air escaping from the intake manifold.
So I suppose one or both of the intake vales are not closing properly..... S#!T !

Before I pull the head again does anybody have any suggestions or anything I should try out ?

Thnaks

[motormanmick]

You need to do a compression test and if it fails the head needs to come off to see what's wrong. If you had put everything back correctly as per original, it should have run fine, so something is wrong. Have you got 2 plug leads crossed over, I've seen that done. I'm hoping you haven't got bent valves. Also I'm assuming you replaced the head gasket and cleaned all surfaces ect.