3cyl gas exhaust valve breakage common?

gears · Jan 27, 2015

So while I'm tearing into this motor ('68 3400) to fix the snapped #3 ex valve I'm wondering if this is a common enough problem that I should order a new valve set for $76 as insurance I won't be putting holes in anymore pistons.

Are these 2piece valves and that's why the head separated mid-stem?

MikeJM · Jan 27, 2015

To my knowledge it's not seen as a common problem. There are several things that could have caused/led to the valve breaking. A flaw near the weld or heat affect zone, valves are friction welded together btw. Excess lash and pounding on return to the seat, a worn guide or bend valve would not help this either as the valve head would make contact on one side or the other flexing the stem slightly.
After the valve dropped is that head ok?

If it were mine and assuming the head is ok I would redo it correctly, check for cracks, check the guides, recondition or ream to the next available size. And a new valve train kit.

gears · Jan 27, 2015

Yeah, full inspection is on my list of things to do.

The head is knicked up but I think it'll cleanup.

I haven't removed the other valves yet to check seats, bent stems/runout or if the guides need reamed.

Even if everything else checks out I'm contemplating replacing all the valves as cheap insurance so I only have to do the job once.

3cyl gas exhaust valve breakage common?

gears

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