No Compression on Cylinder 7

I Have had a week from hell with my Range Rover 4.6 HSE.

The Rover ran fine, it had a small leak from the water pump. I proceded to change the water pump with a new one. To make a long story short.. My car has not run since.

It turns out that the new water pump had a couple of bolt shoulders that were about 3/16th shorter then they were supposed to be. When tightening the new pump on.. I broke the timing chain cover. The bolts went in to far and broke a small piece of the casing which happened to fall into the timing chain........ ( I was not aware of this and proceeded to put the car back together...) After the car would start i found that the timing chain was broken. I replaced the timing cover and I replaced the timing chain. Crank at 12 and Cam at 6. I put everything back together and the car ran terrible. Lots of missing. I then pulled all the plugs and did a compression test. Cylinders 1 thru 6 and 8 have about 125 PSI each. Cylinder 7 has 0 PSI. I took the valve cover off and the push rods are moving the rockers and the cylinder is moving up and down.


Does anybody have an idea as to what the problem could be?

So let me get this straight.... you broke the timing chain accidently, and then tried to crank the engine over? Or you started it... it was running and then it stopped and you found a broken timing chain?
I guess it does not matter either way... but it sounds to me like you may have a bent valve. It is not sealing up... hence the 0 pressure. This would be caused by a valve being in the down position... and the piston coming up and smacking it since the valve would not move if the timing chain was broken.

Just my .02

Hope this helps.
Cheers,
Curly

The engine was turned over by the starter when I didnt know the timing chain was broken, Is this engine an Interference fit? I didnt think it was.

Hopefully you've sorted this out by now, but in case not, I agree with Curly - it sounds like a bent valve to me, too. Most high-efficiency(!), high-compression engines are interference design nowadays, and the 4.6 pushes the limits of the original 3.5-litre block, so I'd say it was highly likely that the piston would smack the valve with the timing chain broken. Can't think of anything else that would have caused the symptoms you describe, either.

Good luck sorting it out.

How did you diagnose this?? I am worried about my car

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Originally Posted by Landlover.Hunter

How did you diagnose this?? I am worried about my car

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Cylinder compression test kit. Remove all spark plugs. Fit tool. Turn over engine. Read guage. Normal pressure should be noted.

To diagnose rings... remove tool. Squirt engine oil into cylinder through sparkplug hole. Refit tool. Turn over engine. If pressure goes up, then rings are failing. Same low pressure, bad valves.

Easy peezy