Engines > Restoration of Model Engines
Restoring 2 inch Case Valve System
Bobsmodels:
I am restoring a 2” Case Traction Engine’s valve system. This engine has been running for about 25 or so years. Operating via belt some attachments for display. I acquired the engine several years ago and noticed it did not run smooth. Having been in the live steam hobby for over 25 years before switching to small model Hit and Miss engines I knew some work would need to be done at some point. Last fall at the last run the engine just would not start unless I flipped the flywheel. I checked around and discovered the steam leaks I had been observing had finally really got out of hand. I had steam coming out of both cylinder cocks and the stack at the same time. I guessed the valve face or something in the steam chest was really amiss. In addition, I could move the valve stem almost a .25 inch when in a notch, indicating the linkage was really worn.
Last month I started disassembling the engine. In the pictures you can see how badly pitted the steam port surface had become. Even the port edges were no longer crisp. I was not sure how much would have to come off and decided to use my surface grinder rather than the mill to clean it up. I felt I could control how much came off more easily. As you can see from the progression I had to remove .041 to clean up the surface. The pitting did not look that deep at first.
As can bee seen the right port edge needs to be cleaned up square, which also means the left port edge will need same amount taken off so there is equal distance from the center of the exhaust port to each side. I am not going to clean up any of the inside edges, just the leading edges at the start of steam admittance. I will need to make a new valve with added length to account for the increased width of the ports.
I have a question about the steam port surface. When reassembled the valve stem will be offset by the .041 I took off. I have two choices. I can make an offset adjustment on the valve stem linkage to account for the .041. Or, I have at one time seen a repair where a thin sheet of steel was made up the thickness of the repair (ie the .041). In that sheet the ports were machined to specification and after the valve face is lapped smooth it could be reused. The advantage of the sheet approach is all the original specs are back on the engine.
I can make the .041 sheet but have some concern about it staying flat and not buckling with heat, given it will be held down by the steam chest and have no way to expand.
My preference is to clean up the steam ports, make a new longer bronze valve (customize its length when setting everything back up), and offset the linkage.
Anyone use the sheet method or have an alternative suggestion.
Thanks
Bob
derekwarner:
Hullo Bob....reading your post interested me, however I have more questions than answers
1. we see the green faced block in the red vice.....is the vice held on a magnetic table?
2. is the block supported on parallel strips in the vice?
3. is the block cast iron or cast steel? [red sparks or yellow sparks?]
4. how did you set the block to be best Law of Fit for initial flatness to start with?
5. is the white grinding wheel A60 or A120 [aluminium oxide?]
6. if red sparks were evident, did the wheel surface load up?
7. are you using coolant when grinding?
In your first paragraph you mention 0.25 inches........so we assume all other dimensions are also in inches!
Point 4. is critical........it is always best to start with a flat clean surface.....the photograph suggests another 0.41" is required for this an so the offfset is 0.082"....[or have I misunderstood?]
The - negative dimensions shown are different between images......nearly as though the block was not adequately supported
eg., right hand top corner = - 0.030, then - 0.091 in another image for the same location!?
how are you measuring the negative depth dimensions?
In some ways, a larger 0.82" would be easier to manage than an offset one 1/2 of this
I have no personal experience with slip steel shim plates, however the prospect is not sitting well :facepalm: in my mind
Derek
cnr6400:
Hi Bob, just a thought - .041" is not a lot to take up. Did you look at the valve to check if it could be used as is just sitting lower on the rod? The valve should float on the rod, usually a few thou rather than .041", but it may work if the valve's shoulders the rod pushes on are still well engaged. If this approach can't work, I'd make a new valve, myself, rather than a thin sheet. I have seen 1/8" thick valve face plates used on some stationary engines.With a thicker plate I'be be a lot less worried about it catching an edge and peeling up like a can lid.... :facepalm:
Also attaching a .041" thin sheet will be difficult to do I think, without distorting it. Just food for thought. :thinking:
Good luck with it!
john mills:
If the valve spindle needs to line up with the valve gear cut a shim gasket between the valve chest and the port face then make sure that the valve has enough clearance to sit on the port face .then the spindle will remain in the same place the vale can just move enough to slide on the port face .
Bobsmodels:
Derek - see below
I agree, the plate will be difficult, much easier to adjust linkage.
Bob
--- Quote from: derekwarner on May 22, 2019, 04:44:37 AM ---Hullo Bob....reading your post interested me, however I have more questions than answers
1. we see the green faced block in the red vice.....is the vice held on a magnetic table?
Yes
2. is the block supported on parallel strips in the vice?
No it was not necessary, see ans 4
3. is the block cast iron or cast steel? [red sparks or yellow sparks?]
Cast Iron
4. how did you set the block to be best Law of Fit for initial flatness to start with?
Block in the vise was set on a surface plate, the unworn four corners of the block were set to within .0005 of each other
5. is the white grinding wheel A60 or A120 [aluminium oxide?]
I do not know I would have to pull it off
6. if red sparks were evident, did the wheel surface load up?
no red sparks
7. are you using coolant when grinding?
No coolant
In your first paragraph you mention 0.25 inches........so we assume all other dimensions are also in inches!
Yes
Point 4. is critical........it is always best to start with a flat clean surface.....the photograph suggests another 0.41" is required for this an so the offfset is 0.082"....[or have I misunderstood?]
I think the problem is with my writing on the block, the dimensions were all the same, ie first photo .020, second photo .030, third photo .041, just sloppy writing.
The - negative dimensions shown are different between images......nearly as though the block was not adequately supported
eg., right hand top corner = - 0.030, then - 0.091 in another image for the same location!? See above ans
how are you measuring the negative depth dimensions?
On the surface plate ie I recorded the start dimension and simple subtraction to get the removed (negative) amount.
In some ways, a larger 0.82" would be easier to manage than an offset one 1/2 of this
I have no personal experience with slip steel shim plates, however the prospect is not sitting well :facepalm: in my mind
Derek
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