Bmarsh1605

Hey all! Looking for some advice here. I had an 08 express van with a 6.0 come In with a #5 misfire. Did some diag and determined it was likely an intake valve issue on #5. Pulled cylinder head and found #5 intake valve was indeed bent and had collided with piston. All other valves/ pistons look ok. #5 push rod and valve spring and rocker all look ok. My question is what could the root of this issue be? Piston came up too high because of bad wrist pin or rod bearing? I didn’t hear any abnormal engine noise other than misfire and exhaust gases whooshing into intake. Valve float or weak valve spring possibly? Auto trans so that kinda rules out possibility of over rev. I’m just trying to get an understanding of what happened so I don’t put this back together and still ha e an issue. Thanks guys!

G Atsma

Check and see whether #5 piston comes up higher in the hole than the others.
ALSO check that particular valve guide for any evidence of sticking of the valve. Excess wear would make the valve **** a bit and possibly stick.

Bmarsh1605

the intake valve was jammed up in the guide for sure. I was able to get it close further with the cyl head off by tapping the valve lightly with a hammer. I wasn’t sure if Valve felt tight in the guide because it was bent or if it got bent because it was tight in the guide. I rolled engine over a few times and it seems to come up about flush with the deck of the block, no more or less than the others

G Atsma

It is tight in the guide because it got cocked from sloppiness in the guide, then stuck open, which in turn caused it to collide with Mr. Piston, bending it and jamming it in the guide.
Not sure this is the reality, but it sounds plausible and makes a good story.

Che70velle

iTrader: (6)

How many miles on the van? I thought 07’ was last year for LQ4...irrelevant here. I’d pull heads and have them gone through if in fact the bottom end is fine. How bad does the piston look?

00pooterSS

iTrader: (40)

If piston was coming up too high it would have likely hit the exhaust instead of the intake, or maybe both, but it would also be hitting the head and there should be witness marks on the piston and the cylinder head.. There's only about .04x" between the piston and head, and you should have far more valve clearance than that. (meaning it would hit the head before the valves).

Due to that I would suspect either a broken valve spring let the valve drop down, or the valve somehow got stuck in the down position due to a funky guide.

Hard to say without being there.

Definitely drop off the heads at a machinist and have them carefully inspected.

And with the heads off rotate the motor until the suspected piston is on the down stroke, then push down on it and see if it falls down any. Check them all for any slop.