Help me diagnose this sound (with video)

[RealMcCoy]

Are the spark plugs out when you're cranking it over in the vid..?

[speedy25]

check your timing marks. Sounds like you have valves open/closing at the wrong time.

That noise is NOT a "knock"

-SP

[Wombat]

Originally Posted by RealMcCoy

Are the spark plugs out when you're cranking it over in the vid..?

Yes, every spark plug is out (i'm using an optima redtop from my good VR-4 and didn't want to completely drain it).

Originally Posted by speedy25;

check your timing marks. Sounds like you have valves open/closing at the wrong time.

That noise is NOT a "knock"

-SP

Dead on. When I went to look at the car, I noticed that the intake cam on the front head was off one tooth. When I brought the car home, I also noticed that the rear intake came was also off one tooth. Since then, I've put the car in time and most likely why I have the compression numbers that I do.

It's just that strange sound that has me wondering. I'm going tp drain the oil and inspect the oil filter and also pop the rear valve cover off and see if there's anything visually wrong.

[Idaho]

in for the carnage...ok not really. hope its something stupid that can be fixed easily.

[RealMcCoy]

I had a couple of possible theories hinging on the answer to my question.... At this point I think your most likely culprit is a sticking valve guide.. I think the valve opens in a normal manner, then hangs slightly and slams shut..

You should be able to easily confirm or debunk my theory by watching the valve operation once you get the cover off...

It could also be something stupid like a collapsed lifter letting the cam slam the valve open, instead of the gradual climb up the opening ramp

[stealthxtreme4]

Subscribed to see what you find out... Definitely interested on that sound. How'd you get the motor to turn over so consistently? lol. I've never seen a starter turn it over like that.

[jay04]

Did u ever remove the valve covers to see anything out of place ie rocker arm?

[Wombat]

Originally Posted by RealMcCoy

I had a couple of possible theories hinging on the answer to my question.... At this point I think your most likely culprit is a sticking valve guide.. I think the valve opens in a normal manner, then hangs slightly and slams shut..

You should be able to easily confirm or debunk my theory by watching the valve operation once you get the cover off...

It could also be something stupid like a collapsed lifter letting the cam slam the valve open, instead of the gradual climb up the opening ramp

Your theory and mine are dead on...glad we think alike I'm hoping it's just a collapsed, sticking lifter that is so bad that the spring isn't letting the valve return back to its closed position and the piston is actually pushing it back. However, if that were the case, I'd still want to pull the head and replace the sticking valve.

Originally Posted by stealthxtreme4

Subscribed to see what you find out... Definitely interested on that sound. How'd you get the motor to turn over so consistently? lol. I've never seen a starter turn it over like that.

Just pull all of the spark plugs. Without those in, you can't create compression in any of the cylinders.

Originally Posted by jay04

Did u ever remove the valve covers to see anything out of place ie rocker arm?

Not yet. That's the next step in this process and I'm going to try to do it tomorrow, although, this isn't the only thing I've got going on in my life (unfortunately), so I have to prioritize. First, I'm going to pull the rear rocker cover and do a close visual inspection and if I don't see anything then I'm going to drain the oil, remove the oil filter, cut it in half and see if there are any metal chunks in it. I'm also going to pour the oil through a fine screen to see if I can find any more metal shavings.

[jay04]

Yes it sounds like its coming from the back but it hard to tell from the video.

[Wombat]

Redid the compression check with the intake plenum off and got some slightly higher numbers on cylinders 1 and 5 (updated in the original post). I also removed the valve cover to check for any signs of physical damage, but I couldn't see anything. I also took another video of me covering up the individual intake runners so you can see why I keep saying cylinder 6 is the problem. I also noticed that there's a bit of backpressure that comes out of the intake runner when it makes the funny sound on number 6. I didn't notice that on any of the other cylinders.

3000GT VR-4 Engine Cranking Noise Part 2