valve seat

[redrider91]

this last weekend i was out at the dunes and somethin broke in the engine. upon getting it home and tore down part of the valve seat had broken out. part was embedded in the head keeping it from running. the other part was below the the head bolt nut opposide of the cam chain. any ideas how it got there and anyone else had this problem?

[bearair]

Typically a valve seat comes loose when the head has gotten too hot. This can happen on any aluminum head engine. The seats are an interference fit into the head. If the head gets too hot, the aluminum can break down enough for the seat to loosen a tiny bit. If it continues to run hot, the seat can break. It may not happen right after the damage was done. It can sometimes take quite some time afterwards, but it's almost always the result of the head getting too hot at some point.

[redrider91]

ok thanks.but what worries me is how it got up in the cam/rockerbox part of the head and underneath one of the head nuts

[bearair]

Can't imagine how it could have gotten up into the valve train unless it poked a hole in the head and came up through.

[redrider91]

no hole in it.its kinda scary