Brum head separation answer

[Deleted User]

Just a couple more points:

A while back now a Round the World Yacht Race competitor had his keel fall off in the Southern Ocean. Naturally the boat turned turtle and resulted in a big rescue operation, some readers may remember the incident. The interesting point is that this was an almost new boat, it turned out that the stainless steel keel bolts had suffered what was called “still water corrosion”. Under certain conditions it seems some stainless steels can fail very rapidly indeed. I regret to say I know little more about this phenomenon but it is now well documented. Therefore if stainless steel studs were contemplated then it would be wise to do a bit of research and be careful about the grade selected. My inclination would be to use conventional high tensile steel, which is better suited than stainless for the job anyway, and maybe have it treated à la Roger Moss.

If you did decide to go the “electrifying experience” route it might be an idea to make a +ve termination that screws on the stud and find somewhere else to complete the circuit. That way there is little risk of damaging the stud threads. Once out of course you can jump up and down on ‘em or throw them at the cat if you want but until then do no damage, you never know what else you may want to try if it fails!

On the other hand if you were to have the studs cut through it might be worth considering trying a stud extractor on the remains in the barrel. I’ve not had too much success with these things but when they work they work well with zero risk of damaging the threaded holes. Which is all very well just so long as the threads are not too tight – you should be so lucky!

[Deleted User]

Hello again fellow forum readers and contributors. My head/cylinder is still doing a terrific impression of one lump of infinitely inseperable metal. Firm in it’s resolve to make my life as short and miserable as possible.
I am not too comfortable in the welding solution for fear of ending up with a bigger lump of trouble. Mig welding is the extent of my talent in that area. Cutting through all the studs seems reasonable but still have the problem of drilling out studs from cylinder and pressing out studs from head as well as copper water pipe renewal. Then of course having someone ship over new studs etc. I have tried attacking each stud individually to loosen with two nuts but studs are terrified of leaving their appointed holes. I have tried a terrific solution that cleans things up very well but cannot get at the aluminum oxide. Frees up a lot of corroded material ,stuck rings etc., but not this. At present it is in the hands of a gentleman specializing in ultrasonic cleaning. I have doubts about this method but have run out of most options I am comfortable with. I forsee in the not too distant future, me packaging it up and sending the *&?%$ thing back where it came from. To someone with a lot more knowledge and experience in these matters. Are you there Mr. Moss. I am in no hurry as the riding season is quickly coming to an end.
Thank you all for your input and suggestions. Very kind.
Brian Rowe

[Deleted User]

I forgot to say, in my last post, that there is obviously a third alternative – the Roger Moss slow soak and custom-made extractor method which has been successfully applied and fully described by Roger.

My only comment about the keel bolt failures in yachts is – thank God we don’t have to put seawater in our radiators! Back in the 70’s a friend and I built a 40′ trimaran for offshore and ocean sailing. It had a centreboard operating inside an underwater casing and relied on a 3/4″ diameter pivot for which stainless steel 316 was specified. We opted for monel – a copper/nickel alloy – on the recommendation of a well known East coast sailor who had carried out a 10 year rebuild in the 50’s of an oyster smack, first registered in 1808. It had numerous bolted elements in its construction, including below the waterline, and he did the whole lot in monel because he wanted it to last another 150 years and metallurgists he consulted wouldn’t garauntee the stainless. It was a lot more expensive. That boat has just celebrated its 200th anniversary, so only another hundred to go.

I am very happy with the idea of cadmium plated stainless studs. A local electroplating firm does silver plating of studs for Wankel engines – very long studs through alloy casings I suppose and this is another slant on avoidance of electro-galvanic corrosion. Any metallurgists care to comment?

[Deleted User]

When I wrote that last bit I just knew that someone would pick up on the seawater thing!

Now I’m no metallurgist but it is my understanding that the villain is chlorides, it is they that promote the stress cracking. The thing is that it is not the seawater per se but the presence of the chlorides that causes the problem and while there is plenty in sea water there is enough elsewhere too, if I read it right as little as 5ppm under the right conditions!

Is this a real problem in this instance? Well possibly, the studs are under stress, (that’s if you remembered to tighten the boogers down!), there is water, there is some heat and there is vibration, not an entirely comforting combination. The really alarming thing is that if all the conditions are just so then the damage can be very rapid indeed, hours rather than weeks it would seem and what is worse the material can appear unaffected, it requires more than a Mk.I eyeball to see the damage.

So would I use stainless? Well on balance probably not, the mechanical properties of high tensile steel, formulated as it is for just this application, has much to recommend it over stainless, the corrosion problem notwithstanding. To minimise rusting I’d certainly consider as fine a finish as possible on the studs, even polishing and then some form of passivation.

The other half of the equation is of course the aluminium head. Is there anything there that can be done to minimise the problems? Well I’m sure there are some fancy and expensive proprietary processes available but if the holes can be cleaned out down to bare metal, sand blasting being my favourite because of the good key that is formed, then the holes can be coated with an epoxy resin. What with the loss of material from the casting by corrosion and by skimping a bit on the stud clearance a sufficiently thick layer to be durable and protective should result. At least no harm will be done to the casting by having a go!

[Deleted User]

Hi Mike
As I reported earlier, I put two well corroded head / barrel assemblies in diesel for two months and then, having made a significant jacking rig then both heads came off reasonably easily. I do have a 250 amp arc welder and could try Doug’s method, so please let us know how you get on.
Whatever method you use to break or reduce the adhesion between the studs and the head, the volume of debris still exists, rather like removing nuts from studs that have been fitted with Loctite. I am interested to know how you will restrain the components after the “treatment” in order to push the head off evenly.
I would hardly expect it will drop off.

[Douglas Kephart]

With the preceding build up the following is unfortunately is going to seem like showing off. But I can add some information to the discussion on the matter of stainless steels. So here it goes-

Stainless steel alloy 316 has the best corrosion resistance properties of all the stainless steels. 316, or specifically the low carbon 316L, is used for medical implants. But even that will corrode invitro, particularly where you have micro-motion or fretting in bolted constructs that continually break the protective surface oxide layer. The small wear particles turn the surrounding tissue a disgusting, but apparently harmless, black color. Besides playing havoc with the MRI image, about six percent of the population is allergic to the nickel content in stainless, and break out post surgery with hives!

316 can not be heat treated, but it can be strengthened by cold working to about 860-1100MPa. There are some cold drawn and extra-hard states that can push that to 1350-1600MPa but it becomes a bugger to machine. It is not the strongest stainless steel available. 440C is a high-carbon martinsitic stainless that can be heat treated to a hardness of RHc60 and 1965MPa. It is used for rust-proof cutting instruments. While it has a high tensile strength, that is solely due to the hardness and it is far too brittle to use for head studs. The 0.2% yield strength is 1896MPa, dangerously close to the ultimate tensile strength of 1965MPa. This means very shortly after it starts to give, it breaks! 420B is also a martensitic like the 440 series and typically used for making injection molds. It can be heat treated to about RHc52, 1724MPa, 0.2% yield at 1482 MPA. A lot of medical instrument forgings (hemostats, forceps) in Europe are made of 420 alloy. It would probably make a decent head stud, but none of the 400 series has exceptional corrosion resistance.

For modest strength applications, like Scotts and side valve Dougles, I will use 17Cr-4Ni, a martinsitic precipitating hardening stainless. Strength and ductility at 1365MPA at RHc44, 1262MPa 0.2% yield. Its best feature is its a dottle to heat treat as it only entails elevating to 900C and allowing to air quench (air cool.) At such low temperatures (relatively speaking) no special atmosphere controlled furnace is required to combat oxidation. The parts do turn a pretty golden brown, but that is about it. 400 series and particularly 440 are more reactive at elevated temperatures and will pit, requiring refractory coatings or an inert purge gas in the furnace. At work we have all 440 processed by vacuum heat treat, or anything else for that matter where you want the parts to stay clean and bright.

Long ago I did try making head bolts for another project in 440C, well tempered so they would not be quite so hard and hopefully more ducal. They snapped under the head radius anyway. Since they actually did not need to be very strong for the intended application, I also tried 304 the next time some was loaded in the bar-feeder on the CNC lathe I was running. They torqued up a bit ‘queer’, and on removal and examination, the 5/16-18 bolt elongated to 5/16-16 threads where the thread emerged from the cylinder! Apparently even though it was not a high strength application, 304 was clearly not good enough! Since then I have paid more attention to mechanical property tables.

Chemical passivation of stainless steels will increase the corrosion resistance. This basically entails a short soak in dilute nitric acid to etch the iron out of the surface, and accelerate to formation of the protective chromium oxide film. 400 series will rust and stain in a steam autoclave if you do not passivate the material. Un-dilute nitric acid will dissolve broken steel taps from aluminum parts, and create evil looking and organically unfriendly brown fumes. Electropolishing also creates a passive layer. Electropolish also takes about 0.02mm off the surface (depending on how long you leave it in the tank and the amount of current passing through the part!) and can affect fine part tolerances.

You could also coat the stainless with one of the Physical Vapor Deposition (PVD) processes, as mentioned by Mike. You still passivate before PVD to remove surface contamination. These coatings are often used on medical instruments to increase wear resistance, and biocompatibility on certain implants. It is also a fairly high temperature process (500C ), so can effect the heat treatment of the material if that is above its tempering range. Coating thickness is typically around 0.005mm. I have used it at lower temperatures of 220C, but was not impressed with the adhesion. There are different methods, Evaporative, Sputtering, and Cathodic-Arc. Primarily the coatings are intended to increase wear resistance- TiN, TiCN, TiAlN, AlTiN, ZrN, etc.; the ones that you see in the cutting tool catalogs. The tempering temperature of tool steels and carbide are safely above the PVD temperature. PVD will also help alleviate galling, which stainless steel threads are prone to, more so than steel. This is commonly encountered with the anti-seize lube provided with the stainless steel spoke and nipple kits.

Cadmium plating will help, but I think a passive layer would work just as well and be cheaper and safer, since cadmium is now considered so dangerous. (Cadmium oxide, particularly as a dust, is fatally toxic.) I use to use stainless safety wire to hang parts in the cadmium cyanide solution, and the plating on the support wires would flake and break off quite easily. No, I do not intentionally try to live dangerously! Perhaps it was because the layer got too thick with internal surface stress, I have seen the similar results trying to heavy hard chrome plate worn transmission shafts, coincidently also a high-nickel content alloy. But it raised doubts as to the cadmium’s ability to really stick to the stainless. On the other hand I read just now in my Handbook of Practical Electroplating that cadmium plating is indeed used on stainless steel aircraft components to prevent galvanic couples with aluminum and magnesium. Personally I have only ever seen cadmium plating on steel aircraft hardware, but then as I said above stainless is not a primary choice for a high-strength fastener. It is probably used on a special-need basis, and an example has not turned up in my surplus hardware; though I have come across the occasional monel fastener.

Any head studs, or any fasteners for that matter, that need strength would be better off in alloy steel. 4140 in B7 (half-hard) condition makes an excellent high-strength stud material and is readily available in small quantities (except the supplier I use skips over 5/16” diameter!) Purchased pre-heat treated to HRc 26-32 it is not so hard that it can not be machined with conventional metal working cutters, and can yield north of 1300MPa with excellent toughness. Heat treated to a full hard state can push that over 2000MPa and still have excellent shock resistance. You can then surface treat it to you liking (phosphate, PVD, Cadmium) for corrosion resistance.

I made new head studs for my Brum in 17Cr-4Ni stainless steel. It has not been Moss tuned but remains in factory specification, so I do not think the studs need to be particularly strong. Consider- the whole block is only held to the crankcase with four slightly larger bolts! Besides I had two studs twist off flush with the head before I tried electrocuting them, and had to make some anew. I do not think the original studs were heat treated (they did not twist off like they were) but they were definitely annealed by the time I was done! There was very little arcing at the top when contact was made. I still have them about somewhere if someone wants to do a gas emissions spectrograph on them to see exactly what their chemical make-up is. I have done this on critical parts like connecting rods and crankshafts on the Dougies, but it did not seem to warrant the expense for a low powered Brumie, the lab test now running about $65. Indeed the rusty originals, annealed and all, would have probably sufficed in this application, but I wanted to make a better job of it and was in the grip of a ‘replace everything with stainless’ fad at the time.

But all this is only needed if your head gasket leaks, as galvanic corrosion only occurs when an electrolyte is present. Bare steel against bare aluminum would be fine if the parts remained dry. O.k. perhaps one can not guarantee sans leaks, you only notice the leaks when the commute to the outside or into the combustion chamber, or you just want an extra margin of protection in case it does leak. So what about the corrosion inhibitors in anti-freeze solutions? These work perfectly well in millions of modern cars with iron and aluminum combinations. I believe there was (still is?) a bias against anti-freeze in Scotts, but that is perhaps best left for a separate topic. Wandering into stainless steels itself has sort of hijacked this post on how to remove stuck cylinder heads!

Disclaimer- I am not a metallurgist. I do design engineering on orthopedic implants, so have come to know stainless steel and titanium alloys in that context. There is not much scope in spinal surgery for cadmium, cyanide, concentrated nitric acid, and high voltages, so I play with those at home…

There are obviously many more stainless steel alloys than mentioned above to suit other requirements. Any good metals handbook can provide the specs and properties, as well as being numerous websites like MatWeb or Carpenter Specialty Steels.

Enough!

-Doug

[Douglas Kephart]

When writing the above I had not read the post about chloride attack. In regards to stainless I can offer no experience, as the presence of chloride in-vitro usually means the patient is on the mortuary slab, and not the operating table.

But it is a problem with machining certain titaniums, as the small quantities of chloride present in metal cutting fluids can attack the titanium. Nothing visible to the eye, but a worry in failure adverse medical and aerospace industries. Chloride-free fluids are specified. Chlorides can be absorbed into iron, and then leech out over time causing serious corrosion. The hull of the Great Britain is a prime example.

-Doug

[Deleted User]

Well done Douglas, that is one very lucid post!

But ‘aint you just gotta love them metric units and these new fangled material specifications?!!! I don’t think I’ll ever get my head around them! All right for the youngsters I guess but how I mourn the passing of human sized feet and inches and the good ‘ole EN numbers!

One thing though, I’ll be glad when this topic is put to bed, I had a dream, (nightmare?), last night in which little chlorine atoms complete with arms, legs and wearing miners helmets were beavering away at the bottom of a crack like manic coal miners!

I REALLY must get a life!

[dave bushell]

In the past, I’ve drilled out the holes in the head a 1/32″ over size and this has helped in removal at a later date but obviously this doesn’t solve Brian’s problem. However, it must be possible to make a thin tubular cutter that could be passed down the studs that will clear the corrosion even at the expense of removing a little of the aluminum around the circumference of the holes.
Dave Bushell

[Deleted User]

Sorry Dave, ingenious but sadly I don’t think that idea will fly; it would be incredibly hard to make such a cutter.
If made to cut only 1/32″ oversize then the wall thickness of such a tube cutter would only be in the order of 1/64″
Remember also that the corrosion products will be both hard and abrasive which would take the edges off the cutter teeth in a trice and even if made hard enough to resist that then the teeth would be oh so very brittle. Also where is the swarf/detritus to go? There is certainly nowhere for clearance flutes or anything like them.
Lastly what would the next step be if, as is entirely possible, the cutter were to seizes half way through the operation?

Anyway, why bother? Sticking the wrenched thing on the milling machine and applying a slitting saw down the gasket line is by comparison a doddle and even if you include removing the stud remains I’ll still wager it’d take less time and at far less risk.

Oh! hell! I’ve already calculated that I’ve got to live to at least 1793/4 to have a chance to finish all the project I’ve already got so what is an extra few days? So if somebody cares to hand me one I’ll do the deed for the cost of incidentals and materials.

[dave bushell]

Hi efra215
I’ve just checked one of the cylinder heads that I removed some time ago and I obviously drilled out the holes to 3/8″ dia. So the tubular drill wouldn’t have been so impractical at 1/32″ wall thicknes.! However, I didn’t think about swarf removal. I guess little but often with deep cut teeth and detritus/swarf removal with an airline. Also I didn’t realise that the corrosion products would be so hard and abrasive. Perhaps a slightly larger tubular bit would only cut through the aluminium – there seems to be plenty of material there and it would then only be a matter of centralising the head on reassembly.
Dave

[Deleted User]

Not only am I no metallurgist I’m also not a mole fiddler, (chemist), I can’t therefore say just how many varieties of aluminium oxide there really are BUT I do know that an awful lot of grinding wheels are made of the stuff! Does not the variety used for grinding wheels known as Corundum comes next in hardness to diamond?

[dave bushell]

I dunnow!!
Dave

[Deleted User]

This thing is getting a bit like the good old camel: “a horse designed by a committee.”

I remain a convinced advocate of

Keep
It
Simple
Stupid

We all get seduced by the marvels of the modern world at times; I’ve observed many a student spend time setting a job up on a machine when a hacksaw or a file would have done the job in half the time.

Which is why I still favour cutting the studs as I’ve outlined because it seems the quickest and safest method.

[Author]

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