Mike Fennel is quite correct, it is impossible to completely decouple the various material in the engine, it is however possible to mitigate the result by sealing off as far as is possible the affected surfaces.
Probably the most potentially (no pun intended!) alarming combination in the Scott engine is the copper gasket / aluminium head combination. On the galvanic scale of common materials they are about as far apart as it is possible to get. I also quite agree that the open design of the smaller holes in the gaskets are a problem. It is possible to have sealing ferrules in these holes as is done for the cylinder bores but there would inevitably be a cost penalty. It is also interesting that many other cylinder head gaskets I have handled have some sort of a “varnish” coating. Now I don’t know what was behind the manufacturers reasoning for this but in our case such a coating would surely help insulate these dissimilar metals.
On the matter of Araldite coatings: The first time I did this was on an antediluvian, (it might well be the actual one Noah used), Johnson outboard motor that had been operated in seawater. For those in the know imagine a horizontally opposed Seagull and you are pretty close. The design of the unit bought some of the aluminium castings into intimate contact with brass components, the inevitable result was that a significant volume of aluminium casting had been eaten away in places. The only repair available to me at the time was to sandblast the damaged areas, make up with Araldite and trim.
Two points should be bourn in mind here, normal abrasive methods, emery cloth, files, wire brushes, etc. do not produce the best key for good adhesion. Sandblasting is about the only method that will get into every nook and cranny and it is vital, as far as is possible, to remove every trace of corroded metal. The thing about sandblasting is that it has the highly advantageous property of raising microscopic “nibs” on the surface that provide the best possible key. It is also advisable to bake the Araldite at between 110 & 120ºC while it is setting, the domestic oven will do nicely but better wait till ‘er indoors is out! Araldite tends to become fluid before it sets and heating will promote this thus ensuring that it will creep into every crevice and also allow the air bubbles that the mixing process inevitably introduced to escape thus ensuring a good solid repair. Unless the surface to be repaired can be laid perfectly flat the Araldite will run, particularly at the temperatures suggested. Therefore for complicated shapes it will be necessary to make a dam to retain it. In the case of the Johnson and other jobs since I have found that plasticine, while it clearly doesn’t like it, will just about stand up to being heated to the suggested temperatures but only the once! The proof of the pudding is that thirty odd years later the repairs are still solid.
The question then is can such a method be used in the stud holes? Clearly the length/diameter ratio presents a problem for sandblasting although as it is possible to blast from both ends it might well work.
An alternative possibility but one that has not been tried and so is offered as an idea, particularly where porosity or corrosion of the aluminium had resulted in penetration of the stud holes from the water space, would be to obtain some thin walled Paxolin or Tufnol tube, the sort of thing used for making radio coils and the like. Carbon fibre tent stays or maybe even mugging a fisherman for his carbon fibre Carp pole might also serve if of the right size. Failing suitable tube solid rod is readily available and making a tube is a simple enough turning operation. The thing is that these materials are suitably inert, waterproof and will readily take an adhesive. In this case, with the original hole suitably enlarged, the tube could be glued in effectively sealing off the aluminium; in this case one of the Loctite products might prove more effective than Araldite. This suggestion might initially appear more involved than lining the holes with Araldite but at least it eliminates the possibility of incomplete coverage and you’d get a clean hole needing no fettling.
One final point; on other engines it has been shown that as large as possible extra thick washers, (say 1/8”), made from a quality steel such as EN24t (817M40) will improve the effectiveness of the torque applied to the studs both by spreading the load on the casting and eliminating flexure of the washer. A light spotfacing of the cylinder head will further ensure a good square contact. Such washers are easy to make and given the quality of the aluminium used on some Scott heads every little will help.
