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Post by Deleted on Jul 19, 2020 9:09:17 GMT
Hi guys, a question for those who have built a loco with this valve-gear. I am currently making the 3 connecting rods and the next job will be the 6 pins that hold everything together. Don's drawing shows 6 identical pins with little wording, these can be seen in the drawing below. Now, my question for you guys is what method did you use to secure the link between the 1:1 lever and the middle cylinder? The pin as drawn can not work as there will be very little clearance, well actually next to zero in as far as the pin's head and the spilt pin required to hold the pin in place are concerned. On looking at this my mind is saying to fit a plain shank pin, equal in length to the overall width of the combined parts and secure it with a grub screw through the middle of the 1:1 gear. I'd include a small dimple in the pin for the grub screw to hold it properly and also give some thought to lubricating it. The photo also shows the 2:1 lever and 1:1 lever closed to show what I'm trying to describe, once the connecting link is made and put in position it will only just clear the opened area of the slot, so no possibility of using the pin as drawn if that's what Don is suggesting, he states to make 6 of the pins in the drawing which is the total amount of pins used for the 2:1 lever. Clearly this is not correct.  So guy's what have you done, does anyone know what's used on full size which of course would be my prefered method to use? Pete |
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Post by Roger on Jul 19, 2020 9:27:42 GMT
Hi Pete,
I would be concerned that a grub screw would work loose, I don't think that's a good solution unless you use screwlock on it as well.
A cross drilled hole with a split pin might be an alternative, or a tapered pin, although I'm not a fan of those. I presume all you're trying to do is to prevent the pivot pin from sliding out sideways?
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Post by steamer5 on Jul 19, 2020 9:42:16 GMT
Hi Pete,
What about e clips top & bottom?
Cheers Kerrin
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Post by Deleted on Jul 19, 2020 9:51:45 GMT
Thanks guys
Yes Roger if using a grub screw it would be secured with a threadlock. I have just answered a siggestion on FB where I thought of using a taper pin, that may be the solution. The other method I mentioned on FB, was a gudeon pin ( think that's the correct name) like that used for the ctosshead. Problem there is all 7/32 holes for bith 1:1 lever and connecting rod have already been drilled for the 5/32 bronze bushes for the pins I might be able to play around with that idea if adapting the bushes?
Afraid there's no room for E clips Kerrin...
Cheers
Pete
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Post by steamer5 on Jul 19, 2020 10:00:38 GMT
Hi Pete,
It was a bit of a long shot. If you were really keen, then circlips? Would love to see how you would do 12 internal grooves for that diameter!
Somebody must of cracked this problem.
Cheers Kerrin
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Post by Deleted on Jul 19, 2020 10:06:38 GMT
Well I know I'll come up with something but always intetested in hearing ftom those who have tackled this on their own model or suggestions from fellow model engineers such as those from you and Roger. I'd really like to find how it's done full-size but so far google has failed me.
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millman
Part of the e-furniture
Posts: 296 
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Post by millman on Jul 19, 2020 10:33:25 GMT
Roll pin?
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Post by Deleted on Jul 19, 2020 10:45:04 GMT
Yes that is also possible although I do need to be careful about drilling right through the pin, it's only 5/32 dia....it will be the same problem with a taper pin although that would probably be a smaller hole. Thank's for the suggestion millman...  Pete |
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Post by d304 on Jul 19, 2020 11:39:45 GMT
Hi Pete
Just an email showing ho Greenly did his in 71/4.
For 5” I would drill and tap the bottom hole of the valve connecting rod to accept a pin with a matching thread at the bottom.
David
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Post by suctionhose on Jul 19, 2020 11:42:28 GMT
It is a problem and not one limited to conjugating levers.
Ideally the pin should be fixed in the fork and only turn in the bush of the piece connected between.
If this is not so, the clevis holes will wear out instead of the bush.
One solution is to harden everything: clevis, link and pin....once worn however, difficult to repair.
My solution, not one you'll agree to I suspect Pete, has been to use a stepped pin secured though one side of the clevis with a nut.
Taper pins or roll pins weaken the clevis unless very tiny as does use of grub screws (for even less permanence).
The only other configuration I have seen used and half consider viable is to bush the eyes of the clevis and the hole in the link with thin walled, glass hard silver steel bushes (no tempering) and lapping paste the hardened and tempered pin to the perfect fit.
In that way the pin can remain free to rotate, retained by a clip or split pin. Life is long and repairs are possible in the future.
The main takeaway from above is do not let the pin move and wear the clevis... unless you are prepared to deal with wear of the clevis holes after a time.
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Post by Deleted on Jul 19, 2020 12:55:44 GMT
hi Ross
Thank's for the suggestions... the 'clevis' section on the connecting rod/link when fitted to the 1:1 lever has no clearance to fit a pin/nut assembly. If looking at the picture when the connecting rod it fitted the void top and bottom of the 1:1 lever will be filled and there isn't enough metal on the forks (clevis) for a pin. So I can only secure the pin through the 1:1 lever itself. Now, all three holes, that's the clevis and the 1:1 lever will have bronze bushes, 7/32 OD and 5/32 ID, or should I say the OD will be slightly bigger for a press fit. So in far as wear is concerned it shouldn't be too bad and easy to repair with new bushes and new pin too if required.
My head right now can only see a plain pin with a small dimple for a grub screw to lock against as the easiest solution. If the grub screw faces forward to where the access door is future maintenance should be fairly easy. removal of the entire assembly would require the fulcrum pin to be pulled out, that's easy with the top hatch access, the 1:1 lever grub screw loosened for the connecting link to be freed and the two outside connecting link pin's removed. With that done it should be easy enough to remove the whole 2;1/1:1 lever out through either side of the frames.
If I had realised this before I could possibly have fitted a gudgeon pin as used for the crossheads. I'd have enlarged the clevis section and thread the lower part of it for a csk gudgeon pin to be fitted. This could have had a slotted head which wouldn't have been seen once assembled. This is still a possibility if I redesign the connecting link although since I have already started this part I'm not that keen to do so.
It would be interesting to see a works drawing as to what they did, I suspect it maybe some form of gudgeon pin?
many thanks for your input
Pete
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Post by silverfox on Jul 19, 2020 13:11:37 GMT
er on the B17 plans it shows for the 'inner lever fulcrum pin
the hole in the 2-1 lever is tapped 3BA i did mine 5/32 x 40 and The top hole is reamed 3/16d the pin is 3/16 d and 7/16 long the threaded part ( 56/32 x 40) is 5/32 long The top is 3/32 depth and 'flattened' to 1/4 AF Hope that makes sense
The pins for the valve rod connections are are bit hard to fins ad Malcolm has the CDO details right up against them BUT he does show something he calls the Inside pin link as i off silver steel 5.32D 15/64 long with a slot cut into it and has a 5/64 length of 4BA He also shows PB bushes. I have sent you a picture on email
Ron
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Post by Deleted on Jul 19, 2020 13:32:38 GMT
Hi Ron
I looked at your drawing, thanks for sharing, that won't work on Doncaster, it has pressed bushes in both clevis parts and the 1:1 lever, clearly designed for a plain pin to go through but with zero clearance above and below the pin, this isn't possible. I've looked at the drawings a few times now, I'll take another look in case I've missed something.
Cheers
Pete
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Post by Deleted on Jul 19, 2020 13:42:53 GMT
Hmm.. ok I've found one mistake on my part, the clevis isn't bushed, it's a smaller hole, no sign of the pin though or words on the subject and it's clearly not showing any countersunk so not a gudgeon pin, perhaps it's a pressed fit? Hope that's not the case as that makes removing the 1:1 lever for maintenance a problem if at all. I'll have to do a few measurements to see.
Pete
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Post by Deleted on Jul 19, 2020 14:55:41 GMT
Well, I have taken another look at Don's words, nothing on the pin, in fact, he has no words to point out the smaller hole in the connecting link either? I have kindly been sent a very helpful picture of an assembled 2:1 unit. To me it looks like there's a hex head bolt doing the same job as the grub screw that I mentioned, I don't think it's a grease nipple but you never know but even if it is, a hex head bolt in it's place should do the job required and also be a point for lubrication.  My current thinking, although this can always change, is to silver solder a small boss where you can see the bolt/grease nipple? in the picture, this will give extra strength to the bolt to hold the pin, bear in mind it's not holding any weight, just stopping the pin from dropping out, a small dimple/recess and a pointed bolt end will stop this, I could harden it too. I will continue making the connecting link as started with bronze bushes press-fitted into either end. This makes the pin static and running in the two clevis bushes, I see no issues with this and the whole assembly will be very easy to remove and fit new pin/bushes if and as required. I've just had a conversation with someone who works on the full-size engine and who sent me this picture from one of the pacific books, he's going to check tomorrow to see what info he can find, my current idea for a solution has the most favour... think's it's a matter of watch this space.. thanks for all the suggestions guys... Pete |
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Post by silverfox on Jul 19, 2020 19:57:39 GMT
Peter
I amagine that picture reversed and rgw viewing point is from the rear, looks rather like the B17 arrangement .The only difference is i have a massive box section stretcher that also holds the inside slidebars in place
Ron
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Post by suctionhose on Jul 20, 2020 10:37:21 GMT
My current thinking, although this can always change, is to silver solder a small boss where you can see the bolt/grease nipple? in the picture, this will give extra strength to the bolt to hold the pin, bear in mind it's not holding any weight, just stopping the pin from dropping out, a small dimple/recess and a pointed bolt end will stop this, I could harden it too. I will continue making the connecting link as started with bronze bushes press-fitted into either end. This makes the pin static and running in the two clevis bushes, I see no issues with this and the whole assembly will be very easy to remove and fit new pin/bushes if and as required. Pete Pete, As per your thoughts above, if the pin rotates in the clevis fork holes, you can secure it in the centre piece with a grub as you suggest or a roll pin or a taper pin (the best IMHO). Another thought I had to secure the pin in the fork, would be to use a Scotch Key. i.e. a small grub screw tapped half in the end of the pin and half in the fork. The thread engagement would prevent the pin coming out. In the end, I'd probably do as you suggest but use a taper pin in lieu of the grub screw. Ross |
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Post by Deleted on Jul 20, 2020 12:31:41 GMT
Hi Ross Thank you for your continued input, still not finalised but am getting closer to what I think I'll end up doing. I have dropped the idea of silver soldering on a small boss as once the bush is pressed it there will be plenty of metal for the bolt thread. I'm also thinking of adding a small step to the top of the pin and give a slight counterbore to the top of the upper bush for the step (lip) to sit in thus removing the possibility of the pin dropping through. A very small grove in the pin for the bolt to locate against would stop any chance of it rising up although if it did it couldn't go anywhere as the unit is encapsulated within the 2:1 lever. I'm thinking more of a bolt than taper pin as it gives me a lubrication point, I may even look to see how large a bolt could be used ( the one in the picture looks doable) and whether this could be drilled for lubricating rather than requiring removal? all just ideas for now. In the meantime, I'm carrying on with the 3 links, I've just machined the slot for the middle cylinder link and test fitted it to the 1:1 lever and also in the 2:1 lever, I'm happy with the fit, just need to file the slot end square so that the link has it's full swing as per Don's drawing. Lot's going on in the CME's head in PSH works today, hopefully my time won't be wasted, fingers crossed.... Regards Pete |
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61962
Seasoned Member
Posts: 129
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Post by 61962 on Jul 20, 2020 16:15:26 GMT
Hi Pete,
Full size the 1 to 1 lever is secured to the inside valve link with a 3/8" taper pin across the lower leg of the fork which half engages the link pin. The small end of the taper pin is split and opened out to ensure its security. Won't work on the model though unless you want to get into watchmaking. Solution on my A4 was to screw the bottom of the pin into the bottom fork with a screwdriver slot in the top. I think it's a 7BA thread on the 1/8" pin so it tightens against the fork. Its been there for more than 40 years and has never come loose.It could probably do with a new one now. I'll adopt the same method on the K3s. The other pins full size are fully floating. They have a washer on the bottom, held in place with a 5/16" split pin which goes into a channel in the washer not quite half the split pin diameter. On my A4 they have a 7 ba nut on the bottom. I fancy the K3s will be as full size with a 3/64 split pin, much as Don's drawing.
Hope that helps
Eddie
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Post by Deleted on Jul 20, 2020 17:54:19 GMT
Thank you Eddie, that's very useful information... I was toying with threading the lower fork, or should I say it's bush as the holes are already drilled to accept them. I wasn't sure if the screw as you describe could be removed while on the model? I think it may is the left-hand link was undone along with the middle cylinder link to the spindle. From my playing around I think it's then possible to pull the unit (link /1:1 lever) back enough to get at the screw from the top running board when removed. Using my current plan is much easier to remove the conjugated valve gear entirely without having to remove any running boards, or at least it looks that way. I'll have a better idea as the parts get made. Can you see any issue if the pin is running in the forks rather than the 1:1 lever bush? This is my only concern/unknown right now, well until I think of any other concerns that is... I have roughed out the link slots today, well the middle cylinder link is to size but the 3/16 cutter became too blunt to continue, I have ordered some from Tracy tools who are usually pretty quick in their response. Not wanting to waste the day I roughed out the other two links with a 3mm cutter, everything is set ready for me to finish once the correct size cutter arrives. Tomorrow I may make a start on the bushes, seems I have no 5/32 silver steel in stock for the pins so they will have to wait... such is life.. Regards Pete Pete |
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