I am appalled that anyone should think I was casting aspersions, why, I’d not even heard the name Doug Kephart until I read it here! I have no reason to doubt his expertise or the accuracy of his report; my thoughts are based purely on what appears on this site.
The devil lies in the detail, just as it takes 10 or more people to put one soldier into the field so a successful outcome to a job such as this depends on a lot of incidentals not the least of which is the expertise of the operator. Was the job done on a Scott engine or another machine, what equipment was available and so on? One clue to Doug Kephart’s success is the statement that, “Doug Kephart’s engineering knowledge and experience is second to none.” Well, fair enough, but I too have done a little bit of hands-on engineering as it happens.
To reply to Mike Fennell’s points, I was not assuming that the whole head would be near the stud temperature but for all that aluminium is a darned good conductor and it’s going rob an awful lot of heat from the stud, inevitably it will get very hot locally. The suggestion that the stud might be brought up to “bright red” worries me not a little, bright red is generally accepted to be about 900°C. and at that temperature the aluminium local to the stud is at considerable risk, 900°C. is, after all, half as much again as the melting point of aluminium. I’m not suggesting that the whole head will transform itself into a puddle on the floor but there is a real risk of local damage. And whatever is the case you’d still need an ‘effing big welder!
On the matter of cutting through the studs, yes, I agree, the bandsaw idea is not the best, it was thrown in as a last resort, all quite possible but not one I’d choose if there was an alternative, there is a real risk of damaging both the cylinder and head surfaces even in skilled hands even though I have in the past successfully and accurately sawn through much thicker sections of more difficult materials than a Scott cylinder.
My method of choice still remains the milling machine.
I do not see the centre studs as a particular problem as they only 1½” in from the fore & aft edges of the cylinder casting and 6″ diameter slitting saws are readily available.
And yes, the threaded remains of the studs would require carefully drilling out of the cylinder casting but while requiring care in setting up it ‘aint exactly rocket science although equally its not a job for a wobbly arm and a pistol drill!
It is customary to drill the tapping hole for a thread slightly larger than the theoretical root diameter of the thread, typically to give a 70% thread; this creates a little void at the root of each thread, which is easily discerned as a dark spiral in the hole when the size is just right. It should only be necessary to progressively enlarging the hole in small steps on the first hole until this is seen. The remains of the stud can then be picked out, with a little luck and accurate centring the remains of the thread may even uncoil in its entirety but if not, (more likely), once the first two or three turns are extracted then the careful application of a plug tap of the correct size will loosen the remainder. A little at a time is the order of the day here, don’t get too ambitious, remove all loosened detritus regularly.
The remains of the studs in the cylinder head can best be tackled with the aid of a fly press or something similar. A straight push is required; I don’t think the bench vice is on for this job. Preferably the head will be sat on a flat plate with a clearance hole for the stud to pass through to support and spread the load on the gasket face. This will prevent localised loading and the risk of distortion.
I still think that sacrificing the studs is the safest option, even if the heating method succeeds in loosening all the studs in the head the head still has to be lifted or each stud has to be unscrewed and with all that rubbish in each hole the likelihood is a minefield of troubles whereas the stud cutting method uses safe, tried and tested engineering procedures.
But then lets face it; if this particular job was a doddle we’d not be discussing it here in the first place!