What happenned to my motor? (catostrophic damage)

[supravw]

Long story short, last November or so I swapped a 4g63 into my colt. Left the bottom end alone, aside from bs elim. The head was newer, 25k on rebuild, all new timing belt components, water pump, etc. ARP headstuds torqued to 100. Started up fine, no smoking, ran good, put about 25 miles on it and I'm driving at 60mph, just cruising and it makes a weird noise and stops running. Won't start again, won't even crank.

Fast forward to now.
I just pulled the motor out and took the head off for the first time. One valve dropped. No other valve damage, and the weirdest part is there is no mark on the piston where the valve would hit (causing it to break). Does anyone know what might have happened??? I'm completely lost.

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And I don't see how there is debris in the other cylinders either...

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See there are no impact marks where the valve could have hit to break it...

 

[sbiggi]

Could have lost a keeper. Valvestem could have broke.

If the valve was bent before the rebuild, that would stress the stem every time it closed the valve and eventually it would break.

 

[supravw]

Could have lost a keeper. Valvestem could have broke.

If the valve was bent before the rebuild, that would stress the stem every time it closed the valve and eventually it would break.

The stem is still in the head, just the head broke off.

The valve being partly bent could make sense, but I would have thought I might have felt it when checking timing??

 

[blcknspo0ln]

The stem is still in the head, just the head broke off.

The valve being partly bent could make sense, but I would have thought I might have felt it when checking timing??

Not necessarily, that valve could have been closed at the time of checking TDC and cranking it by hand for timing. Something along the valve system just got stuck or gave up. I would also check the lifter to see if there's something fishy about it.

 

[supravw]

Thanks for the input, I'll check that out. I've been following your rebuild thread and picked up quite a few pointers that I'll be using on my build. Hopefully I'll have some better luck this time.

 

[Defiant]

Well, the head snapped-off and it just "failed". There may not be anything more to it than that. If that valve got hot, I think you'd see signs of it, and the other valve would look the same. No real sign of unusual heating in that cylinder, from what shows in the head.

"Sometimes things fall apart, that's God's love in disguise"

 

[supravw]

Well, the head snapped-off and it just "failed". There may not be anything more to it than that. If that valve got hot, I think you'd see signs of it, and the other valve would look the same. No real sign of unusual heating in that cylinder, from what shows in the head.

"Sometimes things fall apart, that's God's love in disguise"

So it wasn't my fault!? WOOHOO! I've been thinking what could I have done wrong sense it blew up on me. That's some crappy luck though. Hopefully that's out of the way now and I'm on to enjoying DRIVING my dsm powered mobile!

 

[Defiant]

Even beating the snot out of it shouldn't have popped off a valve head. You'd have been more likely to go out-of-bounds on the fuel trims and burn one before just breaking it like that.