Having worked my way through Technicalities and Son of Technicalities, I am concerned about using stainless head studs on my Scott is born project. Is there any reason why bolts rather than studs and nuts can not be used? in theory it should be much easier to break the corrossion bond by applying torque. Another thought I have had, has anybody tried cladding the studs with heat shrink sleeving, you would obviously need to make the holes oversize to make room for the sleeving. Any comments? Dave Herbert.
The heat shrink sleeving idea should serve although I don’t entirely like the idea of opening out the holes.
If you are determined however it might be an idea to put a thin smear of my favourite rust stopper, wool fat, on the studs and then shrink the sleeving over that. The sleeving will hold the wool fat in reducing any small tendency for it to contaminate the water spaces and at the same time filling any small voids under the sleeving. Polishing the studs to as high a finish as possible will also serve to delay the onset of corrosion.
Alternatively how about painting the studs with a quality two-pack paint? The studs should be prepared by sandblasting if possible to give a really good key.
Another possibility is coating them with an epoxy resin, (Araldite), again sandblasting would be needed for a good bond.
The trick is, as best as is possible, to electrically decouple the studs from the rest of the engine, the dissimilar metals plus the water are effectively a battery so any insulation of the surface of the studs will help.
It has to be sods law, or somebodies, that the day after posting the question, Feb Yowl arrived, and Ray Bayliss answered my question. Thanks also EFR 215, for also answering, but what do you mean by wool fat?, is that the same as lanolin? Regards Dave Herbert.
Wool Fat = Anhydrous Lanoline
Your local chemist will stock it in BP grade. It’s getting a bit expensive these days but unless you are younger than 50 years old a 500g tub will see you out as only a thin smear is needed, it goes a long way.
It is enormously useful for all sorts of wet proofing or rust preventing jobs. For example smeared onto exposed parts, a car’s brake pipes for example; it develops a skin that is proof against anything the roads can throw at it. I first found about it when sailing and anything that can resist seawater has got to be good!
On threads, particularly ones that will be regularly undone, it will prevent seizures while being sticky enough to discourage loosening due to vibration.
A thin layer inside a mudguard will do much to protect the paint particularly by the time it’s collected its inevitable layer of road clag. Nature’s own stone chip protector!
It even has a DIY use around the house, dip a woodscrew in it and it drives in much more easily, makes a better thread in the wood thus a better grip and stops them going rusty in the wood too.
As I’ve said on here before: When you last see a rusty sheep?
If I am storing ferrous finished items in my main store shed over winter, I spray them with a lanolin liquid using a cheapo Wilko sprayer. It has been made for years and is often known by the generic title Shell Ensis Liquid.
Almost all oil companies make an equivalent and it is effective and economical. A thicker grade is produced that is excellent for car body underside protection. Both can be brushed as well as sprayed.
There has been a lot of comment about studs corroding making head removal difficult. I agree, but I ask why remove the head anyway.
The barrels can easily be bored without removing the head, just like a blind barrel. By all means take care if you have to fit a head. Make sure the head is flat and pull the head fixings down a little at a time in correct sequence, then leave 24 hours and see how much the nuts have become loose. Finish tightening, run engine about 15 minutes on light load, let cool, re tighten then a decent run let cool and tighten again. Scott gaskets are thick and spongy. it is like seating the head on a matress. If you do not tighten progressively and evenly, you are in danger of bowing the head. They are not made of high strength alloy and must be treated with care. After fitting the head correctly, you can forget it and just treat it like a blind head block. I suspect that on many occasions heads are removed without that really being necessary. Roger
Recent postings on this perennial topic have focussed on preventing the studs rusting. Fair enough. But will these ideas prevent the galvanic action which causes formation of aluminium oxide on the head? I don’t think so.
I doubt if there is any way of eliminating electrical contact between the head and the block – consider the presence of the copper gasket, firmly clamped between those components, plus head nuts and washers. Can you exclude the hot electrolyte from the the stud/head spaces by use of sealant? No, because the gasket asbestos is porous.
All this means, in my view, that a method of coating the inner surfaces of the head drillings will be needed. efr215 (I believe) has previously suggested epoxy in slightly enlarged holes. Epoxy resin will adhere to aluminium but its adhesion can be greatly improved by abrasion of the surface through a coating of fresh, uncured resin. This removes the oxide layer and the resin prevents the instant re-oxidation which normally occurs in air. I think this would considerably reduce the production of aluminium corrosion products which are the principal cause of all the grief. Roger’s practical knowledge and advice on head tightening are, as usual, very relevant and useful.
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.