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| Piston and Valve Yoke Repairs https://www.rypn.org/forums/viewtopic.php?f=1&t=35081 |
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| Author: | 610BS [ Tue May 28, 2013 5:56 pm ] |
| Post subject: | Piston and Valve Yoke Repairs |
Need some advice regarding the piston and valve rods for a Porter locomotive with 6x10 cylinders. The rods are pitted. Are there any options for repair or should they be replaced? Is it possible to remove the piston rod from the piston without destroying the entire assembly? Some Porter drawings show the rod threaded into the piston but I'm not sure that applies to these. Thanks, Dave Attachment: image1.jpg Attachment: image2.jpg
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| Author: | Dave [ Tue May 28, 2013 6:15 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Hello other Dave. Glover built by Porter clone. Cool. Anyhow, please let us know more about the locomotive itself and the service in which it is going to be put. Under light private circumstances many things are possible that wouldn't be a good idea under heavy use on a regulated railroad. It is likely that the piston rods were either pressed or screwed into the pistons, then the ends hammered down to prevent their working loose. Air pump rods are still installed that way. If you want to replace the rods, I'd chuck it up in the lathe and start to bore out the end of the rod from the center of the piston intil the hole in the piston itself becomes visible. Then, heat, beat and twist the rod loose. The valve rods are of course forged. If you want to try to fill in the pits with something like braze, then turn and burnish or grind smooth, it might work. Hard chroming won't fill pits but will put a smooth surface on a decently machined rod. You might try an aluminum bronze or silicon bronze wire in a MIG welder for filling in the pits...... The valve rods don't have near the mechanical stress on them that the piston rods do, so simply fabricating and machining a new set of valve rods wouldn't be difficult. If you are going to just putter around the back yard now and then pulling nothing much, you could turn the rods down somewhat, but not much......and then adapt the packing gland to take a thicker rope packing without extruding back into the piston. So, it depends on many things. Tell us more for better advice. dave |
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| Author: | atsfm177 [ Tue May 28, 2013 6:32 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
My preference is to flame spray and then machine to original diminsions. It is a cross between a welder and a paint spray gun. It sprays molten metal onto the shaft while it is spun in a lathe or similar device. I've used it on lots of different types of shafts. Greg |
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| Author: | 610BS [ Tue May 28, 2013 6:45 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Dave, This is a former Detroit Yukon Mining Company locomotive, built in 1904, weighing 7 tons wet, with a tractive force of 10,000 lbs. The intent is to run it on private tracks, a couple times, just to see it run again. Thanks, Dave |
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| Author: | Dave [ Tue May 28, 2013 7:30 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Cool. Take a few light cuts off the rods, no more than about 50 thou, and polish with emery cloth. Make a brass washer to fit the smaller rod to go into the gland, and get some nice soft graphited teflon packing that will be a tight fit. Drop the pressure way down to a hot fog - presume you've done some boiler surveying and know what you have to work with safely. Dont sweat a little bit of a leak - the valves and piston rings will blow by, and the rope packings willl open up until they have seated through numerous tightenings. I'd get a hone and go through the cylinders before putting it back together. Have fun with it. Best wishes and send photos. dave |
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| Author: | sbhunterca [ Tue May 28, 2013 8:04 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Quote: My preference is to flame spray and then machine to original diminsions. It is a cropss between welder and a paint spray gun. It sprays molten metal onto the shaft while it is spun in a lathe of similar device. I've used it on lots of different types of shafts. A shop I used to work in did a lot of spray welding of worn shafts. It was often far cheaper than manufacturing a new shaft, and could be machined or ground. This was my first thought when I saw the question. Steve Hunter |
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| Author: | Dave [ Tue May 28, 2013 11:15 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Yes, it does build up - but one guy doing this in his garage isn't likely to have that handy. Occasional light service can be done less critically and with simpler methods. dave |
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| Author: | 610BS [ Wed May 29, 2013 6:28 am ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Appreciate the advice... I know of several reputable companies doing spray welding but I need to check into it further. Last time I checked they were spraying stainless and I'm not sure if stainless would provide a suitable bearing surface. Also, I need to find out much material must be removed to provide sufficient adhesion. With the movement being along the axis, there should be less of a concern with the adhesion. Thanks, Dave |
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| Author: | Dave [ Wed May 29, 2013 8:38 am ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Stainless and steam don't always play nicely together...but that's been more a concern in terms of pressure vessels and piping among model live steamers and seems to vary depending on the grade of stainless. I tend to avoid it since I have no reliable understanding of what the problems are and how to avoid them. Don't overthink. dave |
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| Author: | filmteknik [ Wed May 29, 2013 9:36 am ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
How deep is the pitting? Is turning off a few thousandths going to appreciably affect the strength of the shafts? This is just a guess but I think on a rotating shaft the farther from center the more load each tiny bit is carrying but on something that is in purely linear motion isn't it all stressed more or less evenly? If that's the case then wouldn't the reduction in strength be in proportion to the metal removed? Like if you turn away 1% you reduce the strength 1%? (Maybe not...that's why I'm asking. I am not a machinist.) Steve |
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| Author: | Kelly Anderson [ Wed May 29, 2013 9:53 am ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
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| Author: | 610BS [ Thu May 30, 2013 7:37 am ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Many thanks for the ideas and advice. This Monday, I'll be discussing the options with several shops which specialize in thermal spray repairs. I'm also going to see if I can locate the Porter drawing for this size piston and rod. It likely won't be of any use for actual sizes but it might tell me how the rod is secured. Thanks, Dave |
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| Author: | 610BS [ Mon Jun 03, 2013 5:51 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Just to follow-up... After weighing the piston rod assembly and doing a quick calculation, I realized the pistons are hollow thus I'm not sure if I want to put them at risk replacing the rods. The end of piston rod is headed or peened over to secure the piston on the rod. The diameter of the rods would be reduced by about 20 thou to remove the pitting and resurface the rods. Companies I spoke to, which do both hard chrome and HVOF tungsten carbide, said it really makes no difference. Cost is basically the same and they claim there should be no issues with adhesion or cracking. Personally, I think the tungsten coating looks a bit too high tech, with it's dark gray appearance. Now, I need to decide if material should added. This would give the rods some extra corrosion protection. I'm told the extra material could be stripped and reapplied in the future if desired. Thanks, Dave |
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| Author: | Dave [ Mon Jun 03, 2013 7:07 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Twenty schmunty. Take a cut and follow with a polish and call it good. You won't need to change anything else. My old friend Harold told me the pits in moving parts are there to carry the grease into the bearings. We were discussing his crankpins at the time, but it might work here too....... dave |
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| Author: | NYCRRson [ Mon Jun 03, 2013 8:46 pm ] |
| Post subject: | Re: Piston and Valve Yoke Repairs |
Turning them seems simple at first, but the one time I tried that the rods where not as straight as they look. Don't be suprised if they are bowed by .010" to 0.050" in the middle. Hard to take off just .020" when the middle is already offset from the ends by 0.050". Works if you can take off 0.050" or more to overcome the bow. And you usually need a good deep cut on the first pass (deeper than the pits) so the tool does not jump out of the cut when it hits a pit. Once it jumps out then your final polishing work just got harder and longer. It may work fine, but for just puttering around I would tend to polish them up with emery in a lathe and call it a day. If the pits are smaller than the depth of your packing things should still seal up pretty good. good luck. Cheers, Kevin |
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