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New piston/combustion chamber shape


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Soft on power, but ran amazingly well half a lap back to the pit.  No funny noises or anything, I was expecting to find that I had simply dropped a plug wire.


Looks like it was just fatigue.  One of the other intakes has a teesny flaw showing in the same location. Should have changed the valves out last season.

Tach memory said peak 8500 which is normal, sometimes a little closer to 9K.








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Michael Deilke

Whidbey Island, Washington


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Think the seat dropped first?  It's comprehensively....  mulched...


wait, no, it's been cut in half, hasn't it...




I've never (so far) had the head come off a valve.


Breaking a rocker's quiet like that- except that, when you go back to power,

there's a particular engine note that says, 'Oh, by the way, we've got 3 cylinders and one vacuum pump'



"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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We call that Reving for Dollars.  I'm with KB how many hours on those valves?  This from someone that had a valve with less than 15 hrs on it do the same thing at Monterey a few years ago.  

1970 1602 (purchased 12/1974)

1974 2002 Turbo

1988 M5

1986 Euro 325iC

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I can't remember where those valves are from or if they were all matched.  It looks like an exhaust have been quickly replaced somewhere along the way because it didn't have its stem necked down like the others.  But we (me and my motor/flow bench buddy) couldn't remember doing it and we're the only ones who have ever touched my heads since 2008. No idea the hours, I used that head for a couple seasons then switched to a 121 for a while then back for the last couple seasons..so quite a few hours..too many.

No fault of the parts, I run the stuff way too hard for my budget:) 


The seat could have dropped first, I've had that happen, the reason I don't think it happened this time is that the valve head and its edges are in amazing condition and the valve pocket looks pretty good too.  There is no extra valve clearance to play with in that motor, so if the seat started to drop I would expect a few smacks of the piston with the valve head in the approximate correct neighborhood. No valve diameter marks in the pocket.  This looks more like the head came off followed the piston down, rotated and got shoved through the roof on the first or second hit.  


None of the normal broken motor or broken rocker sounds, just instant soft power like a dropped plug wire. The stem end shows the waves of failure as the crack progressed maybe 10 cycles until past halfway and then it just let go.


Nose of the rocker got a little mushed when one of the big chunks shoved back hard, but not mushed like what happens when the cam is pushing and it has nowhere to go


Michael Deilke

Whidbey Island, Washington


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