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Post by Roger on Nov 25, 2013 8:28:19 GMT
At the risk of being burnt at the stake, has anyone used miniature ball bearings to replace the small end bearing of the connecting rod where I'm told there's the most wear? If you search ebay for "miniature ball bearings" you'll find loads of them for absurdly low prices. I've used them in other projects and they seem very good. I'm also tempted to fit them to the valve gear where bronze bushes are specified, they won't be seen and they should last a lifetime. In any places where they might be seen, like the eccentric rod, there's enough room to fit a ball bearing and add a thin bronze cover to give the right appearance. Doubtless this is heresy to some, but it's a practical response to a miniature engineering problem. Obviously the main coupling rod bearings need a little clearance so they can't be replaced, but I'm looking into using 'Oilite' bearings for those. These can be purchased in metric sizes that can then be machined to the imperial fits required.
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Post by Deleted on Nov 25, 2013 11:55:43 GMT
My understanding is that ball/roller bearings are considered to be unsuitable where the rotation is not continuous - something to do with the oil film breaking down due to the oscillating motion of the balls/rollers not spreading the oil film. Having said that, people do use them in valve gears. They are also used in coupling rods and big ends by our American friends. Perhaps for our use, the loads are considerably less than the bearings are designed for so lubrication is not so critical.
For coupling rod and connecting rod bearings I've used bearing grade PEEK with success. Gives the crankpins an easy life. Might be worth looking into the Vesconite that Pondok is going to use for his new rod bearings.
Another thing you might like to consider is fitting the axle boxes with sealed needle roller bearings and using unhardened silver steel for the axles. No need for a hardened inner sleeve - the silver steel is more than hard enough. It makes for a very free running chassis and the bearings will probably outlive you!
John
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Post by sparticusrye on Nov 25, 2013 16:03:14 GMT
I've used the minature ball bearings in my R/C Car for years. They are 10mm OD with a 5mm ID for the hubs. The car can reach speeds of 50 km/h, wheels are 50mm in diameter, and the bearing last forever as long as the seals are in good condition. I would imagine that in valve gear with the lower RPMs they would last indefinately, though I haven't tested it. Would be interested to see it in application.
I'll be interested to see your speedy progress. Something about the 15xx that is desirable. I've had to book for Speedy for sometime but haven't made an attempt because of the known issues. If you publish the corrections to a wiki I would be tempted to start one. Once I've completed my Emma Victoria which is slow going at the moment.
James
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Post by Roger on Nov 25, 2013 19:54:50 GMT
My understanding is that ball/roller bearings are considered to be unsuitable where the rotation is not continuous - something to do with the oil film breaking down due to the oscillating motion of the balls/rollers not spreading the oil film. Having said that, people do use them in valve gears. They are also used in coupling rods and big ends by our American friends. Perhaps for our use, the loads are considerably less than the bearings are designed for so lubrication is not so critical. For coupling rod and connecting rod bearings I've used bearing grade PEEK with success. Gives the crankpins an easy life. Might be worth looking into the Vesconite that Pondok is going to use for his new rod bearings. Another thing you might like to consider is fitting the axle boxes with sealed needle roller bearings and using unhardened silver steel for the axles. No need for a hardened inner sleeve - the silver steel is more than hard enough. It makes for a very free running chassis and the bearings will probably outlive you! John Those are very helpful and interesting comments John. I think it's a common misconception that if something wears, you have to make it harder to resist it. The company I used to work for had dreadful problems with aluminium vacuum fittings being eroded by fibre glass dust being constantly sucked through them. They changed them to steel with little effect so I suggested they coat them with silicone sealant.... problem solved. I know it's not the same as a bearing, but intuition isn't always a good guide. I like the idea of using the kinds of materials you mention, at least you won't have to replace both parts! Igus do materials like that too, and Glacier have a range of steel backed bearings. As for ball bearings and oscillation, I think this can be solved by replacing the oil with high speed bearing grease. This is exotic stuff and we used to use it on all of our ball bearing spindles we repaired professionally. Some of these ran to 60,000 RPM with a bearing inside diameter of 15mm, not your run of the mill application for a greased bearing, and not easy to get right. Anyway, this grease would remain in contact with the balls and wick the oil to where it's needed on these miniature bearings. I'll take a look at sealed needle roller bearings, that sounds quite attractive.
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Post by Roger on Nov 25, 2013 20:08:37 GMT
I've used the minature ball bearings in my R/C Car for years. They are 10mm OD with a 5mm ID for the hubs. The car can reach speeds of 50 km/h, wheels are 50mm in diameter, and the bearing last forever as long as the seals are in good condition. I would imagine that in valve gear with the lower RPMs they would last indefinately, though I haven't tested it. Would be interested to see it in application. I'll be interested to see your speedy progress. Something about the 15xx that is desirable. I've had to book for Speedy for sometime but haven't made an attempt because of the known issues. If you publish the corrections to a wiki I would be tempted to start one. Once I've completed my Emma Victoria which is slow going at the moment. James Those bearings are remarkable, aren't they, it's amazing the abuse they'll put up with. I've ordered a couple of sizes for SPEEDY, 4mm x 8mm x 3mm wide and 3mm x 7mm x 3mm which should do the small ends and the valve gear parts. Initially I didn't think they'd fit, but of course you don't need such a large diameter pin and there are some very compact ones. In fact, there's room to put two in side by side on the small end of the connecting rod. Those small ones cost £6.75 for 10 pieces, free delivery. It's cheaper than buying a piece of Phosphor Bronze to make them in the traditional way! To be honest, I don't think SPEEDY has s many issues as I first thought, even though some are pretty fundamental. Certainly there are some gaffes with the clearance of the front brakes, the boiler lagging, the dodgy valve gear and the incorrect back to back wheel dimension, but enough have been built to know that it's not a basket case. I'm happy to share whatever I've learned and supply whatever drawings of the modifications I make. I've made the frames now, complete with most of the holes it's going to need and the horn blocks are almost ready to be riveted on. I'm itching to crack on with the valve gear if I'm honest. Computer modelling is all very well, but I'm here to make something not just play at the keyboard.
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Post by suctionhose on Nov 26, 2013 12:16:32 GMT
Hello again Striplar, Pleased to hear you're on the way with the frames.
Re bearings: The greatest enemies of mini bearings is water, dirt and ash. Sealing is vitally important. We run 5" on the ground. There may be less dirt on elevated tracks but still there's rail rust and ash from the fire. People use needle rollers on valve gear that do not have enough arc of movement to lubricate properly or "roll". Alignment is always an issue requiring careful management of end floats so joints are not subjected to bending. I've seen them fail or rust up having got water in them. Not worth the trouble in my opinion.
Sealed balls or greasable cannon boxes for axles are satisfactory. So are bushes!
A couple of points about steam loco bearings: 1. Wear is a product of load and speed. For a given bearing area, slow moving surfaces can be more heavily loaded the fast moving surfaces. 2. The fastest surface speeds on locomotives are crossheads and eccentrics. These are usually of generous area and not heavily loaded (marine engines with short con rods often had water cooled slides) 3. Axle bearings are usually both generous in area and low surface speed. Bushes lubricated up the centre of the axle NEVER wear out! 4. Rear axles under narrow fireboxes are always problematic due ash. Oil injected up the axle centre to force the dirt out of the bush works very well. Care is needed to keep dirt / ash out so far as possible. 5. Valve gear pins and bushes reciprocate rather than roll. A bush is best. The pin must be tight in the fork of the clevis and secured so that it cannot "flog" All movement must be in the bush. Often I fit two narrow bushes leaving an oil chamber about 1mm wide between them. 6. The leading crankpin behind the crosshead is normally narrow and tends to wear more than the others. 7. Oilite bushes are OK if space allows a reasonably thick wall section. Solid bronze is better because you can make bushes with only 20 thou wall section and they still press in tight. A sintered bush will just crumble.
The secret of success is accurate alignments, good fits and enough of the right oil. Use a tacky oil that doesn't throw out or breakdown with reciprocating loads. (I use a Rock Drill oil - chain bar oil is tacky too)
One 0-4-0 we had travelled 6000 kms over about 10 years! We ran it at clubs in 4 states, regular passenger work on open days and around the house on the home track at all hours of day and night! We wore 1/4" off the wheels and a 1/16" off the axles. We never changed a bush - maybe the little ends once - the crossheads, cylinders, eccentrics were all fine and only required minor attention during the big overhaul at the end.
The right oil is what makes the difference!
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Post by Roger on Nov 26, 2013 20:57:40 GMT
Many thanks for that, I'll chew that lot over! I'm probably going to make the axle bearings as designed, but make a sizable covered oil reservoir in the top of the axle boxes. I hear what you're saying about dust and ash, others have suggested a deflector plate for the rear axle. I can see how ball and needle bearings can fall foul of rusting and that they probably need to be kept filled with grease. I have a superb grease that has the consistency of light mayonnaise and could completely fill a ball bearing. There's room to put close fitting covers on those so my gut feeling is that it ought to last forever but I may be wrong. It's not difficult to change to a bush if it doesn't work. I do like your idea of a split bush though, with an oil reservoir in between. I suppose a similar thing would be to partially part a bush in the centre and just cross drill into the bore so that you keep more bearing area. Anyway, tis and cunning plan and I rather like it. It's something that I may well use on all of the connecting rod bushes, a kind of buried reservoir.
I've looked up Rock Drill Oil and there seem to be quite a lot of different grades from ISO grade 46 to 320! Perhaps you could let me know which one you use? I'd also be interested to know what oil you use for the axles. That's an interesting comment you make about bushes lubricated 'Up the Centre'. I'm not sure how to interpret that really. Does that mean fed up from the bottom of an axle ie where there's no load? How to you achieve that in a split axle box? 'O' rings and drill ways come to mind but I may have got the wrong end of the stick, I'm good at that.
It's good to hear that the right fits and lubrication can give excellent life, that's making all the right noises for me.
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uuu
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Post by uuu on Nov 26, 2013 21:16:28 GMT
Up the centre: you can drill in from each end of the axle, far enough to get to where the bearing surface is. then a cross-hole. So it's very easy to apply oil-just squirt in from the ends.
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Post by ejparrott on Nov 26, 2013 21:43:54 GMT
I've got some greases' at work specifically designed to be water resistant, I'll try and remember to get details of them when I'm back in on Thursday
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jma1009
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Post by jma1009 on Nov 26, 2013 21:53:51 GMT
wilf, yes perhaps, but totally non-prototypical. proper oil reservoirs on the tops of the axleboxes with oil feed pipes from above if you cant get at the oil reservoirs through the spokes are to be preferred IMHO. cheers, julian
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Post by suctionhose on Nov 27, 2013 11:05:35 GMT
Yes as uuu said you drill the axle down the axis and have a a cross hole half way along the bush. Not prototypical, no, but of the variety of axleboxes available, definitely the simplest and longest lasting in my experience. (you have a centre in the axle anyway. Just have a 60 deg tip on your oil can. Appearance is the same. Watch for access behind the crosshead - was a problem on the 2-8-0) Here's a pic of the "prototypical axle box on the 2-8-0 mentioned earlier. It has a felt pad in the bottom half. These are a lot of work to make! Fortunately, cast iron doesn't wear - you cut diamonds against it - but I did have to remake the axle under the ashpan due to ash and grit blocking up the oil supply and lapping the steel away. If using a bush with the centre lube as above there's no need to split them. They never wear out! Oilite would be good in this location. I can think of at least 3 engines I made this way, 2 are 20 years old and one is 30 years now. Back to Rock Drill Oil: I'm using Shell Torcula 320 with Molybdenum Disulphide. When we started out in 1973 they told us at the club to use cylinder oil in the bearings. We found bushes needed replacing at 200 hrs. After Dad changed to Torcula nothing ever wore out again! I have no need to look for better although I'm sure other oils and certainly other viable materials for pins and bushes exist. Ross
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Post by Roger on Nov 27, 2013 11:20:38 GMT
Up the centre: you can drill in from each end of the axle, far enough to get to where the bearing surface is. then a cross-hole. So it's very easy to apply oil-just squirt in from the ends. Ahhhh, now that's a clever idea! I'm going to have to ask the obvious question though... doesn't the oil want to drain back out? I can see that it's going to soak the felt pad though.
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pault
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Post by pault on Nov 27, 2013 11:21:32 GMT
Hi A couple of things to consider regarding bearings in addition to the points already raised, even using 2 off 3x7x3 bearings for the little end you will have the capability to run them right at the top end of their dynamic load capacity assuming 80 psi boiler pressure. Remember that wheels on the same axle do not always lift evenly which will twist the con rod. A self aligning or some type of spherical bearing would probably be more appropriate for the little end. The loads imposed by the twisting will probably exceed the dynamic load on their own. For this reason self aligning ball races are frequently used for the return crank end of the eccentric rod on walschaerts valve gear, certainly in 7 ¼” gauge. If you are going to run roller bearings directly on axles/pins etc I would personally have them case hardened and ground. You can get away without but sometimes you don’t if you follow the manufactures spec it will last a very long time. Do not be tempted to use through hardened silver steel pins or axles it will probably end badly. One of the beauties of bronze bushes is that if you get the clearances wrong the loco will very quickly create the correct clearances. If it is a properly engineered commercial bearing job with no clearance something will give. That said you may be able to get the clearances by using looser fitting bearings like a C4 grade or similar. I wish you luck but it may not be as straight forward as it seems As far as traditional methods go I would leave about 2-3 thou clearance on all connecting rod and coupling rod bushes use a self aligning ball race on the return crank end of the eccentric rod and make all the other valve gear pins snug but free. Axles in axle boxes roller bearings remembering to radius the flanges of the boxes so one wheel can lift without the other one lifting. As far as side float on axle boxes go it depends on the wheel arrangement, distance between wheels and the curves the loco will be going round. Piston’s I would give about 3 thou assuming cylinder and piston are the same material, and about 2 thou on piston valves To tolerance properly is difficult because we all work to different standards with different equipment and have different ideas on what is right. Julian and Taff will tell you that a worn out GWR engine had the same clearances as a new LNER one. I will tell you that is why the LNER were faster and freer running than the GWR. Also that the GWR locos were so poorly made they would fall apart if the clearances (knocks) got any bigger. Ok Ok I’m sorry In some respects talking in microns in this environment and many others is a little pointless when you consider that a micron is smaller than a grain of cigarette smoke and is 0.000039” there’s no point In specifying a tolerance of +.0002”-0.000” if you can only measure to 0.001” This is not meant to be negative and will hopefully be of some help Regards
Paul
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jma1009
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Post by jma1009 on Nov 27, 2013 11:35:37 GMT
hi paul, im surprised you didnt add the LNER jibe that GWR locos will float due to all the corks fitted on the oiling points! cheers, julian
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Post by suctionhose on Nov 27, 2013 11:58:12 GMT
Ahhhh, now that's a clever idea! I'm going to have to ask the obvious question though... doesn't the oil want to drain back out? I can see that it's going to soak the felt pad though.[/quote] Sorry, I'm not being clear. The axlebox pictured has a pocket under the lid. You reach between the spokes with a scriber, lift the lid and poke the oil can spout in. Oil finds it way down the grooves to the felt pad which keeps wiping the axle clean and oiling it. There is no drilling in the axle here. The drilled axle system just feeds a normal bush. The oil doesn't run back out - no air coming in. In practice a quantity of oil remains in the hole and continues to feed the bearing by capillary or centrifugal force or magic or some combination of all three. The important thing is that oil is pressured - use a good can be metal pump not plastic rubbish - into the bearing and pushes dirt away rather than carry it into the bearing. Paul mentioned using a spherical joint meaning a self aligning race. Hard to seal properly - the cap is only one side... But on that theme I've used a spherical joint in the crosshead for the little end. They are called "spherical plain bearings" and they are fantastic if you have the space to fit them. Anyway - enough free tricks of the trade for now! (only joking) Ross
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Post by Roger on Nov 27, 2013 12:09:36 GMT
Hi A couple of things to consider regarding bearings in addition to the points already raised, even using 2 off 3x7x3 bearings for the little end you will have the capability to run them right at the top end of their dynamic load capacity assuming 80 psi boiler pressure. Remember that wheels on the same axle do not always lift evenly which will twist the con rod. A self aligning or some type of spherical bearing would probably be more appropriate for the little end. The loads imposed by the twisting will probably exceed the dynamic load on their own. For this reason self aligning ball races are frequently used for the return crank end of the eccentric rod on walschaerts valve gear, certainly in 7 ¼” gauge. If you are going to run roller bearings directly on axles/pins etc I would personally have them case hardened and ground. You can get away without but sometimes you don’t if you follow the manufactures spec it will last a very long time. Do not be tempted to use through hardened silver steel pins or axles it will probably end badly. One of the beauties of bronze bushes is that if you get the clearances wrong the loco will very quickly create the correct clearances. If it is a properly engineered commercial bearing job with no clearance something will give. That said you may be able to get the clearances by using looser fitting bearings like a C4 grade or similar. I wish you luck but it may not be as straight forward as it seems As far as traditional methods go I would leave about 2-3 thou clearance on all connecting rod and coupling rod bushes use a self aligning ball race on the return crank end of the eccentric rod and make all the other valve gear pins snug but free. Axles in axle boxes roller bearings remembering to radius the flanges of the boxes so one wheel can lift without the other one lifting. As far as side float on axle boxes go it depends on the wheel arrangement, distance between wheels and the curves the loco will be going round. Piston’s I would give about 3 thou assuming cylinder and piston are the same material, and about 2 thou on piston valves To tolerance properly is difficult because we all work to different standards with different equipment and have different ideas on what is right. Julian and Taff will tell you that a worn out GWR engine had the same clearances as a new LNER one. I will tell you that is why the LNER were faster and freer running than the GWR. Also that the GWR locos were so poorly made they would fall apart if the clearances (knocks) got any bigger. Ok Ok I’m sorry In some respects talking in microns in this environment and many others is a little pointless when you consider that a micron is smaller than a grain of cigarette smoke and is 0.000039” there’s no point In specifying a tolerance of +.0002”-0.000” if you can only measure to 0.001” This is not meant to be negative and will hopefully be of some help Regards Paul Very good points. I've had another look a the small end of the connecting rod and I can fit a 4x9x4 single bearing there which should be able to accommodate a small amount of twisting. They're designed to work with axial preload and there's a certain amount of give in them. I don't thing spherical bearings are available in these small sizes but I'll look. The loads on the valve gear shouldn't be that great with piston valves anyway. I'm probably going to go with the split axle box design simply because I don't want to have to ever take the wheels off the shaft. I know that's unlikely to be necessary, but it's a headache I can do without. Ok, I've made a note of those clearances, that's a great help. It would appear that my use of the word microns is giving the wrong impression. I only use it because it's the natural subdivision of a millimiter. When I talk about 25microns, I've just saying a thou in old money, nothing more. It just so happens that there are quite a few of them in a thou, that's all. It doesn't mean that I want something to be 25microns precisely. I know a lot of people are uncomfortable with these units and think of them as infinitesimal but that's really not the case. I don't take anything I read here as negative, I read and absorb every comment in the spirit that it was meant and it's all helpful. My background is in Air Bearing Spindle repairs, so getting 25mm diameter bores 40mm long that are honed to within 2 microns of being parallel is what was required. That's tricky enough without taking into account the size it was and that it had to be within a few seconds of arc true to a mating face. None of this was done with particularly special equipment or laboratory conditions, just care and understanding of what's possible. Obviously it's completely inappropriate to apply tolerances such as these to the kinds of things we're making here, but maybe you can see why then someone talks about fits, I'd like to have a handle on what they mean. Someone's precision fit is someone else's 'stick in a bucket' fit, it just depends on what you're used to.
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Post by Roger on Nov 27, 2013 12:17:54 GMT
Ahhhh, now that's a clever idea! I'm going to have to ask the obvious question though... doesn't the oil want to drain back out? I can see that it's going to soak the felt pad though. Sorry, I'm not being clear. The axlebox pictured has a pocket under the lid. You reach between the spokes with a scriber, lift the lid and poke the oil can spout in. Oil finds it way down the grooves to the felt pad which keeps wiping the axle clean and oiling it. There is no drilling in the axle here. The drilled axle system just feeds a normal bush. The oil doesn't run back out - no air coming in. In practice a quantity of oil remains in the hole and continues to feed the bearing by capillary or centrifugal force or magic or some combination of all three. The important thing is that oil is pressured - use a good can be metal pump not plastic rubbish - into the bearing and pushes dirt away rather than carry it into the bearing. Paul mentioned using a spherical joint meaning a self aligning race. Hard to seal properly - the cap is only one side... But on that theme I've used a spherical joint in the crosshead for the little end. They are called "spherical plain bearings" and they are fantastic if you have the space to fit them. Anyway - enough free tricks of the trade for now! (only joking) Ross[/quote] Ok, I've got it now, and yes, I really like the idea of a covered oil reservoir on top of the axle box. I think this is the way I'll be going. I'll avoid putting the drill way into the top of the bearing, it can go forward or back from there. I suppose there's nothing to stop me from drilling down, past the split (with an 'O' ring seal) to a blanked off cross drilled hole feeding the felt pad reservoir. If that's the ideal solution, then I'll do that, it's easy enough. I do have form when it comes to going over the top at times. That's how a simple hoist for lifting my rotary table turned into a full blown travelling crane. Oh well, it was fun to do, and really useful for moving machines around too.
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Post by suctionhose on Nov 27, 2013 22:22:48 GMT
To be honest, as long as oil gets in and dirt stays out they'll last forever. Axle boxes are the largest and slowest moving bearing surface in the whole engine!
The later-day American practice for driving boxes was to have just a small pad of white metal on top of the axle - for only about 30 deg each side of vertical centre line - and that was all.
Roller bearings in bogies became common. Timken being a household name in rail engineering. Roller type bearings for side rods where used in some cases but they where quite complex to accommodate the alignment issues. A bush, drilled with a myriad of holes and free to rotate against hardened and ground surfaces (pin and rod) were very successful. (the Santa Fe Big End)
Out of interest, Australia purchased some 4-6-4's from North British in the early 50's (Victorian R class). They had roller bearings. during the voyage to Australia the gentle motion of the ship caused slight movement of the rollers which "Brinelled" the races under the weight of the engine. They were all stuffed on arrival! Rolling bearings have to roll...
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Post by Deleted on Nov 27, 2013 22:29:58 GMT
Hello all------------ here's a classic case of a "Brinelled" needle roller bearing from an automotive universal joint....The needles don't actually roll 360 degrees in use but oscillate thus giving that distinctive look when worn................. holdenpaedia.oldholden.com/images/3/3a/Uni_preview.jpg ---------------
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Post by Deleted on Nov 27, 2013 22:43:40 GMT
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