13-08-2017, 10:48 PM
(13-08-2017, 09:18 PM)Ian Williams Wrote: Hmmm, impressive! What sort of CR, valve lift, and valve springs do you run? Very flat tappets and a hell of a lot of load on the the poorly supported valve chest side, possibly casting core misplacement since manufacture or other casting flaw leading to stress fracture???? Will be fascinated to know what you eventually decide is the reason.
Runnng 5:1, modest valve lift (Paul Bonewell) who also did the tappets to match. Valve springs are doubles, which I may choose to downgrade in the rebuild.
The mode of failure, as I see it, is either 3 studs break (rear and two rear-most offside), block lifts in that corner, breaks the base flange around the remaining offside stud, block pivots but is firmly held by the through bolting on the near side so breaks under the valve chest.
The alternative is that the block flange on the off side breaks first, leading to the 3 studs breaking and the same outcome for the valve chest.
I'll run the block through the bandsaw in due course to see whether the casting was weak from the start. Looks thin.
Charles