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The only thing that does that is the pistons hitting the valves.

I did that at high RPMs, about 7000, but it was only one valve.

It sounds to me like whoever put the cam in did not check for piston to valve clearance; the chains are loose at startup, until the oil pressure comes up, so that's probably when they hit.

This is the first time I've heard of this particular problem.

If the valve is moving sideways, the guide is cracked or worn badly.

I'd pull that motor, and go over everything carefully; you could have broken chain guides or something.

The heads have to be reworked at a minimum; the valves are probably bent, and at least one guide is bad.

Do a teardown, and post pix.

There will be marks in the carbon on top of the pistons, showing what happened.
 

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Discussion Starter #22
Thanks Grog, that was my initial thought as well. PTV contact or loss of oil pressure. There is no side to side play in the valve, it's in there very tight. Tight enough that it will not budge. It is possible that this was not a factory cam and it was installed incorrectly. Aside from giving everything a visual inspection, I put the motor in as it was from the original seller, so no clue if the cam was factory PI or not. I'm going to start tearing in to it this weekend, and will post up some pics after.
 

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I was looking at the cams listed in your sig; Comp XE268's.

Loss of oil pressure will either cause the rods to knock/seize, or the cams to seize; Cams break chains if they seize.

Valves only fail like that if they hit something.
 

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Discussion Starter #24
I was looking at the cams listed in your sig; Comp XE268's.

Loss of oil pressure will either cause the rods to knock/seize, or the cams to seize; Cams break chains if they seize.

Valves only fail like that if they hit something.
Ahh, got it. I need to update my signature. Those cams were in the original motor, but when it blew I essentially replaced it with what I thought was a stock '02 Mustang GT motor. Update: I got the top end off and I am close to having the front cover off as well. The timing chain going to the head with the stuck valves is extremely loose, I suspect what I will find when I get the cover off is either a failed tensioner or broken guides. Either way I will get some photos up of the results. Taking my time here, but hoping to have more info this weekend.
 

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Discussion Starter #25
Here is what I found when I finally got the timing cover off this weekend... Looks like the passenger side tensioner has failed. It also looked like the guides were toast on that side as well. Next step is to get the head off and over to a machine shop for new valves, guides and seals for the three that were damaged. Anyone have any ideas as to what could have caused this? Also, I was under the impression that the 02 and 0 GT's came with the plastic tensioners without the ratchet system, which leads me to believe that the previous owner may have replaced these in the past.

36903
36904
36905
 

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The 03 cars definitely had plastic.
36906
 

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Discussion Starter #27
Update: I got the passenger side head off this afternoon, and was a bit surprised to not see any PTV contact on the pistons. I ran the car for a while after the issue started so it's possible that all of the un-combusted fuel had washed off the marks. Anyways, after I got the head to the machine shop they determined that 3 of the intake valves and guides were bad (I am assuming this means bent, but I didn't ask the tech to elaborate) I should have the head back on Thursday and will start getting things put back together, hopefully before it starts getting colder.
 

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Discussion Starter #28
Alright, I have the head back on and torqued down. I made sure to put the head on with the pistons down to avoid PTV contact when putting them on. My next challenge is timing the pistons/cams since I have pulled the whole thing apart. From what I can gather I need to pull the cams off, and set the #1 piston to TDC, and from there the cams should go back on with the timing marks in the 12 o'clock position, and from there I line up all of the timing marks with the chain end links. My question is, how do I know if the engine is in the intake or exhaust stroke for TDC? Does it matter since the ECU is using the cam sprocket as a reference does it automatically know?
 

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You’re way overthinking it. Simply lay the chains flat and Mark the links at each end that are vertical, and just line the marked links up with the crank sprocket dot (at TDC) and the cam sprocket dots. Dot to dot, simple as that.

You can do this with the cams loose but I prefer to have the followers removed. Then just rotate the crank with the keyway facing straight left where all pistons aren’t at TDC and pop the followers back in with a screwdriver.
 
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