Having entrusted Siegfried's cylinder head work to Stu Rogers who has extensive experience of Norton open head hairspring motors it was astonishing to find myself standing next to one of these exact bikes whilst debating the Siegfried work. Upshot is that inlet valve guides are unobtainable although exhaust ones are. Stu has measured up the old guides and found them to be standard length, 45 mm and outside diameter, 14mm. The central bore is 9 mm which matches the valve stem diameters. However this should be 8mm for this sport model. Also the inlet guide should be shorter than the exhaust but these are the same length. After much discussion we agreed to say damn the torpedoes and go for 2 exhaust guides and see how that goes. Stu is concerned that we are repeating a previous blunder but lacking length measurement of the inlet we are stumped. At least we know it worked before even with a broken inlet valve. So new valves and 0,3mm oversize guides are on order.
Sent from my BlackBerry 10 smartphone.
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