[Douglas Kephart]

James,

Residual appendages from earlier days to brace the headlamp. My Brum has a bolt and washer to cover the holes in the side, the ones in the top yoke are left open like yours. Presumably to collect rain water…

-Doug

[Douglas Kephart]

I think the chrome is there but worn down from time.

No. It is a picture of my speedo that I sent to James. The bezel is off because I had it re-plated; it and the glass have yet to be reinstalled.

-Doug

[Douglas Kephart]

Geoff,

Presumably S1299 would also be in 1962, which is always what I understood my Brum to be? (Reg 675BWW)

-Doug

[Douglas Kephart]

Must be an awesome bit of kit and I’d love to know what they use as a lubricant.

Probably something high-tech like Sperm whale oil! 🙂
No matter, being military they probably just replaced the gearbox every two hundred service hours!

-Doug

[Douglas Kephart]

I figured the oil groove was eccentric when I read it, and thought what a rather clever idea.

With the oil groove concentric, the pressure of the oil in the bottom of the groove is equal all the way around. So it is only the depth of the groove that provides the ‘head’ above and beyond that provided by centrifugal force. Most of that centrifugal force is being wasted pressing statically against the bottom of the groove. If there were no hole to bleed it off the oil in the groove would just lay there (while the engine was running.) But make the groove eccentric, and the amount of eccentricity is added to the effective depth of the groove resulting in more oil being directed to the oilway leading to the crankpin. That is assuming the extra amount of oil can pass through the oil way. Otherwise it will just spill over the groove wall, because at any given point the height of the groove wall is no greater than before. The practical test carried out by George Silk with the lathe and paper to capture the pattern of the oil being slung off the crank suggest indeed the oilway can pass the additional oil directed to it that would otherwise be wasted. It should be clarified that more oil is not being introduced to the system (via the main bearings), just that less is being lost overboard, resulting in more getting to the oilway.

Could these modifications be made to existing cranks. Well why not? I know original Scott cranks are heat-treated and tempered, but are they hard? Harder than plain steel yes, but uncuttable? My understanding is (and correct me if I have this wrong because I never thought to test mine) that they are not case-hardened. I presume this since they have demountable races that are dead hard. Therefore the crank can be tempered for maximum toughness, not hardness. Now 300M, 9310, 4340 steels heat treated but not case hardened (indeed you should not case harden 4340) can be cut in the tempered state with carbide tooling. Not particularly long tool life, but doable. Actually fairly easily with Cubic Boron Nitrite tipped tools (even steels up to 72Rhc, I have done it.) Now I do not know if CBN tipped tools were available in the Silk era, but certainly carbide was. The cheapest way to experiment would be to grind up an carbide tipped undercutting lathe tool (or buy a solid carbide radius grooving tool for about $50), offset mount mount in a chuck, and have a go. But practical experience suggests that though the carbide may be hard enough to cut the tempered steel, you may get a lot of chatter because you have too much cutting edge engaged continuously in the cut. In a softer steel you might get away with it. In these cases I have had better luck (less chatter) with milling, and rotating the part with a rotary table. You can readily buy half round milling cutters (sort of like a Woodruff key seat cutter, but with a full radius) in solid carbide for about $80.

Another point brought up with modifying existing cranks is the oilway leading to the crankpin will need to be re-drilled. Why? Granted the opening for the oilway will be above the new ‘floor’ of the groove. But you do not need to drill a new hole, just elongate the entrance to the oilway (with a Dremel moto-tool and a small grindstone) till it is flush with the bottom of the groove. The oil will flow sideways into the aperture, and flow into the original drilling. Right?

Anyway, I though it sounded intriguing and viable. Anyone want to try it? 😀

-Doug

[Douglas Kephart]

Roger,

I have to admit I had to read that passage in the Yowl twice; ‘did he just say what I thought he did?!’ I was going to write a response, but figure, naw, it just had to be an oversight. But if you have not already done so, you should send in a clarification identifying (most important) and correcting (less important) the wrong bit, as there probably are a lot of folk that do not know any different and are going to accept the whole as gospel based on your excellent reputation with Scotts. To err is human, but to ‘fess-up is manly (an point fingers is politic!) You have sort of hinted about it here, but for those reading this that are wondering what bit is the fuss about, specifically it has to do with the rollers needing to skid to equalize the difference in circumference between the inner and outer race of the big end. At first this may seem like an profound anomaly, but in reality the rollers can maintain contact without sliding by the effect called precession. The difference between the distance traveled by the roller, rolling against the outer race compared to the inner race is made up by the rollers advancing – or proceeding – around the crank pin. This can be easily be demonstrated to non-believers with a caged ball bearing (before seals hid the action.) Holding the outer race and rotating the inner the cage rotates with, but at about half the speed, as the inner. For those that still insist some small amount of skidding must be going on, silence them by give the analogy of a planetary gear train. The teeth do not allow any slippage. There is a lot of thought provoking ideas in what you contribute, so I would hate to see the less technical folk left to wonder what was the wheat and what was the chaff. Though they do say a little bran is good for the diet!

Of course rollers can skid under certain circumstances. Snapping the throttle open in neutral or ‘blipping’ was always said to be unkind to the rollers.

I do have some other thoughts to toss into the fray on the subject of eccentric crank oil grooves, but there is another post specifically on that subject so I will place them there for debate. I would be interested to see if anyone thinks they have any merit.

Best regards,

-Doug

[Douglas Kephart]

As a North American member I am effected by the spares embargo. Though since I have not really been doing much on my Brum, it has not really mattered! Several other Brit Bike clubs I belong to or know of are in the same boat, and none of them have found a viable solution. Only the larger clubs of 2K plus members seem able to absorb the increased insurance premiums.

When I first joined the SOC, I deposited fifty quid with the Spares department. Before the advent of PayPal and exact amounts, I would pay my dues with the next higher denomination, rather than put coins in an envelope. So the amount grew a little each year as I was not drawing on it. When the whole Spares financial debacle came to pass, I figured the 50 quid evaporated, as a query about spares a year prior to that went unanswered. So I was mighty surprised when they transferred the funds from the old Spares scheme to the new, to be notified I had a balance of some seventy quid. Which due to the embargo I could not now use! I had the option to then cash out, but I decided as long as I continue to be a member, to consider it a loan to the Club in good faith. To pull the money out just because I can not directly benefit seems petty to me. After all I am sure they can use all the funds they can get, and it is not always about what the club can do for me. Some folk (gasp!) actually volunteer their time to help run and manage the club for the rest of us. I am sure there are plenty of members out there that would pay 70 quid to stay off the committee and avoid the hassle! Should the present world financial meltdown (another NA initiative) render me so strapped I need that 70 quid back, then I will be in a bad state indeed. I wonder if the Club goes insolvent, will the British government bail them out like the Royal Bank of Scotland Group?

Nor do I envision there will ever be a solution to the insurance problem; in fact I expect the UK and Europe will eventually be drowning in their own litigious environment. Just look at the invasive spread of Health and Safety into more and more aspects of common life. While talk of building up the Spares is laudable, I would get some advice as to the future trend on liability insurance and if the inevitable increase is going to be exponential. I could see it in twenty years that smaller clubs in the UK will not be able to afford general liability insurance let alone insuring manufacture of spares. Doom and gloom maybe, but not impossible that the Club may be out of the spares game entirely. I have wondered why the smaller clubs have not banded together as a co-op to buy insurance, but probably organizing such and making sure member clubs did not cut corners and jeopardize the whole scheme is probably logistically too big a task.

-Doug

[Douglas Kephart]

For considerably less you can also download copies of old patents (for free!) via-

https://gb.espacenet.com

Select the Advance Search link and enter in what details you know. British patents will be prefixed by ‘GB’.

So to look up the fork patent enter GB150944 in the Publication Number field. Or you may try Scott Motor Company in the inventor or applicant field. Or search a keyword in the Description field. Enter only ‘GB’ in the Publication Number to limit the search results to just British patents. Hours of fun.

-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

[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]

Oh-oh, who is this Doug Kephart and why is he causing so much trouble!

I confess it was I that took an arc welding machine and attacked a poor defenseless Brum. Yes I did it, and yes it did work very well. I did try penetrating oil and warming the head up with a propane torch and letting it cool, to no avail. But that was it as far as preparatory work goes. I had heard of others using the hacksaw method, but even with grinding the set off the teeth I was worried about damage should the blade wander off course. The head gasket looked mighty thin, and it sounded like a very laborious task. I was afraid I would loose patience, rush it, and ruin the job. Hence my thoughts along the lines of the old electric rivet furnaces.

The reason Mike that you may not have been able to find the original reference in the Yowl is that was a quite a while ago, Vol.17: No.5, August 1991 (good grief time flies!) Second, it was buried in the middle of a three part and never finished saga on restoring my Brum. It was not an article specifically on the topic of removing stuck head studs.

Mike PM-ed me querying about the original article, and I gave him a summary of the technique and results, but I have to confess I did not check back on the forum till now (another PM) to see what came of it. Only to find I seem to have gone ‘missing’! The three Brum restoration articles and violence with an arc welder are copied in the Technicalities 9.2.18, general restoration topics.

Now to address some of the points raised, particularly the concern about melting the surrounding aluminum. There are a couple of reasons that explain why this does not happen. The stud (if stuck) is surrounded by aluminum oxide, which is a fair electrical and thermal insulator. When confronted with that route or a nice direct path down the stud and into the cast iron block, the current takes- well- the path of least resistance. But probably the main reason the alloy does not get hot, is that there just is not enough time. As I recall it took twenty seconds at most to turn the stud incandescent. No doubt some of the alloy immediately around the stud gets hot, but it does not get near melting temperature. The rest of the aluminum surrounding it is a fairly effective heat sink and the heat transfer from the stud through the aluminum oxide is poor.

I was using a 250amp arc welder. An industrial model, but since I was only using it for twenty seconds at a time, duty cycle rating did not factor in to it. I did not experiment as to how little current it took; I had 250amps on the dial, so of course I set it to maximum! The result was zero to glowing red in twenty seconds. Based on that I do not believe you need 300amps, but that would heat the stud up much quicker. I could not say what the minimum amperage required would be. If you only had say a small 125amp hobby welding machine, then it might take too long to bring the stud up to heat. The aluminum will then have a chance to heat up and expand with the stud. That still might break the corrosive bond and so enable the stud to be removed. In either case axial elongation as the stud heats up will help break the grip of the corrosion. But I think most of the gain was through rapid expansion of the stud and compaction the aluminum oxide. Then as the stud cooled, it pulled away from the surface of the hole. When I finished with a stuck stud, it actually had a slight amount of clearance in the hole; the stud backed out freely. There was a hard ‘skin’ of discolored oxide in the hole, backed up by a softer, powdery oxide. Nor were the threads stuck in the block.

Worst case is if the resistance heating was too slow, you could have time to transfer enough heat from the stud to the aluminum to melt it. But I think this would be rather difficult to achieve because of the thermal conductivity of the surrounding aluminum pulling the heat away. You would have to heat the aluminum through to the water passage right up to the melting point to get it to sag, else it has no where to go, even if the material right next to the stud did start to get a little ‘soft’. One could fill the water passages with water if it is a concern, but it may be easier to find a larger welding machine and get the job done quickly, or use the saw method. It would be a different story if the current were flowing through the aluminum. Remove the cylinder head nuts so that you do not accidentally create a circuit through the head.

One point made in the original article, but not here on this forum, is to make sure that the cylinder block is well grounded. Trying to pass 250amps through too small a contact area will cause arcing. This happened to me, and it burnt a small chunk out of the cylinder skirt. Making sure the skirts were sitting flat on the steel work table (which was grounded to the welding machine) seemed to be sufficient to stop the arcing. I did not have to go to the trouble to find a place to clip the ground cable to on the block, or make a special grounding lug to bolt on.

This method has come up before on the forum in 2004 in John E. Smith’s post of 15Jun04; re- his stuck head on his 1949 Flying Squirrel, where I have a follow-up reply. I think it was in the preceding post referenced, wherein incredulity to resistance heating was aired. I am pretty sure I responded to that and outlined the method used. I could not find that specific post, but note the date mentioned of 16Apr04 seems to just predate the oldest post on this forum, so it must be on the old forum prior to implementing registration. There use to be a link to the old forum, as a sort of archives, but I do not see that now.

I hope this clarifies the method that I used. It is not a method for everyone due to equipment or nerve, but it did actually work. Once…

-Doug

P.S. “metalastic bush”

[Douglas Kephart]

@Roger wrote:

…I hope you will not mind if I copy your piece for my records.

Sure.

Chemical testing of the original parts was one part curiosity, and one part to set a baseline for a minimum requirement. I found it interesting that the optimum material available today, was very similar to what they chose some eighty years ago! Of course they called it something different then and it was not so refined. Add to that cryogenics and specialty coatings, and there is no reason not to exceed the original specs (except for lack of funds!) After all we put a man on the moon; why not a Scott back on the road?

-Doug

[Douglas Kephart]

A similar situation exists with Douglas motorcycles of the twenties and thirties, though on rare occasion they will call out a specification relevant to the time. So 5% nickel steel might be given as Hughes & Johnson X84 (proprietary), or S82 (a post WW1 aircraft spec.) Cross comparison, when you can find charts, would show them equivalent to EN39b. They started using material similar to EN36 going into the mid-1930ss.

But the only way to really know is to have a sample item sent to a metallurgy lab and tested. Usually this is an optical emissions spectrometer, where they vaporize a small patch of the surface material. Then you get a precise record of the chemical make-up and percentages there of. The lab may tell you if it is similar to a current material, otherwise you have to find the nearest match using a metals handbook.

Chemical tests on ferrous materials were running $30 in 1997 here in the USA. I think the price doubled since the lab I used changed ownership! Fortunately (?) there are an abundance of broken Dougie crankshafts and connecting rods about to test.

When I made new connecting rods for the Dirt Track Dougies, the nearest equivalent I could find was SAE9310. The modern steels do not have as high nickel content (4.25% is usually the highest offered), but they more than make up for it in purity, constancy, and refinement. Most of these specialty steels are made for the aerospace industry, and they do not tolerate variation, or slag inclusions! The bar stock is invariably vacuum re-melt, Timken of bearing fame does quite a sideline in specialty steel and have a good website with lots of steel spec info. Also available now is more precise control over the heat treatment process, with furnace temperature control to within two degrees and inert atmospheres. Something not available back then at all is cryogenic tempering of ferrous parts to -300 degrees F. In essence this extends the tempering range. The upper limit is fixed by drawing the hardness out of the part, but the lower limit use to be room temperature, but now it is much lower. So you can cycle the part through some seven hundred degrees rather than just say four hundred of old. End result, more refinement of the metal structure during tempering. And it is not that expensive; around $1-2 per pound processed, or fixed prices for popular items like connecting rods, crankshafts, brake rotors, and target rifle barrels.

For highly stressed case-hardened parts SAE9310 is the best with SAE8620 almost as good but far less expensive and more readily available. For through hardened parts with the maximum shock resistance, SAE 4130, or for thicker sections SAE4340, or the ultimate and hardest to source 300M (a modified version of SAE4340) are usually the best choices. It is a pity you can not case harden some of these through hardening steels, as they have some awesome tensile and impact properties. As always, you have to match the ideal steel with the specific conditions it will be used in, and there the lab or the heat treatment firm can often provide some free advice.

-Doug

[Douglas Kephart]

I had not thought of trying Google for something like that. But the only Google hits I could get for Metalastic bush were for car suspensions kits.

But I did find them available stateside from DomiRacer. They have an on-line store via their website, http://www.domiracer.com and the part numbers for Metalastic bushes for Girling motorcycle suspension units that might be of interest to Scott Birmingham riders are:

#19-64533645 3/8 bolt, 0.940 wide
#19-64533652 3/8 bolt, 0.880 wide
#19-64533658 3/8 bolt, 0.750 wide

They list for $US7-8 each depending on size. They do have sizes for other bolt diameters too.

They just retail stuff, so someone out there is making them but I do not know who.

Cheers,

Doug

[Douglas Kephart]

The Ariel specilist in Gloucesteshire is:

John Budgen Motorcycles
Toddington
PH/FAX: 011 44 1242 621495

I bought one of his replica Drilastic saddles to eventually fit to one on my bikes.

-Doug

[Author]

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