Putting the 1956 Dominator 99 away from a run today, I noticed for the first time what looks like casting blow holes on each side of the cylinder head in the root of the fins adjacent to the carburettor inlet tract. Clearly shown on the attached photo. The holes appear to go directly into the inlet tract. I will remove the carb and check. I spotted the holes as I was checking where the oil was coming from which collects on the cylinder head fins. Some oil I know Is leaking from the two rear head holding down bolts as previously reported.
Being new to Norton’s it seems strange that the holes are there on both sides. I would appreciate your comments.
Hi George, from the photo the blowhole could well be caused by corrosion as it is an ideal location to hold moisture, (condensation) given the staining on and around the adjacent fins and fin roots. It might be useful to try to gauge the depth of the possible hole using some locking wire or other similar thin wire. If it is a through wall penetration don't despair, it can be repaired. All though it is a fairly specialist job a good experienced weld should be able to fill the hole with brazing rods. My experience in this type of repair is limited but I have seen it done in a fully tooled up industrial workshop environment.
Thanks John for your reply. The staining is from the oil leaks and the head was spotlessly clean when I rebuilt the top end. I am surprised that I did not notice the holes when I cleaned and assembled the head initially.
When I have delved deeper I will report back. George
It looks to me that the holes for the carburettor stud has broken through? If that is the case. I wouldn't worry about it as it won't allow air in or fuel out. My 650 head has a tiny hole near the end of one carb stud. If you think it goes through, an easy test with the engine running is to squirt some oil on it and see if the speed alters.
It looks like the casting as it came out from the foundry and I would doubt the hole goes anywhere near the inner wall of the inlet tract. Well worth testing though for peace of mind.
I know the top stud hole is open ended so a good chance the bottom one is the same.
If in doubt get it laser welded. No heat or distortion to worry about.