Main crank pin on different axle then Eccentric on

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heislerboy
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Main crank pin on different axle then Eccentric on

Post by heislerboy » Sun Oct 14, 2018 6:01 pm

I have a set casting for a Milner C-19. Its valve gear is Stephenson and has the eccentric and main drive crank pin on the second axle and the one that I am attempting to modeling after Rio Grande Southern 42, which is a C-17 and has it on the third axle. I know that having them on them on the same is proper. Would having the eccentric on the second axle and the main driver crank pin on the third axle be a problem? My frames is all ready set up for having the eccentric on the second axle and there is no room on the third axle for eccentric because of the firebox for the boiler.

Andrew Sach
42-4.jpg

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Dick_Morris
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Re: Main crank pin on different axle then Eccentric on

Post by Dick_Morris » Sun Oct 14, 2018 10:06 pm

It's a goal to have the minimum of slop in the valve gear. It's also good to have a bit of slop in the rods and so that the locomotive won't bind from the wheels moving up down different amounts due to track irregularities. Your proposal would probably work, but would wreck havoc with the valve events due to all the additional lost motion. Could you move your boiler back with a longer smoke box to give you some room? You could hide the joint where it meets the smoke box with the jacket.

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Marty_Knox
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Re: Main crank pin on different axle then Eccentric on

Post by Marty_Knox » Mon Oct 15, 2018 6:44 am

Locomotive builders did it, at least, Porter did. In fact, small Porter 0-4-0s had the eccentrics on the lead axle, with the blades going back to the link, and the rocker between the drivers. Don Young's Marie E and Marie Estelle are made this way.

KenG
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Re: Main crank pin on different axle then Eccentric on

Post by KenG » Mon Oct 15, 2018 7:29 am

Denver and Rio Grande no 1 "Montezuma" had the same arrangement Marty describes. This was done to get the front of the firebox as far forward as possible up against the driving axle.

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Doug_Edwards
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Re: Main crank pin on different axle then Eccentric on

Post by Doug_Edwards » Mon Oct 15, 2018 7:57 am

I believe the JW Bowker at CRSM has this arrangement also. Not necessarily optimal, but practical.

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RCRR
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Re: Main crank pin on different axle then Eccentric on

Post by RCRR » Mon Oct 15, 2018 9:12 am

I'm thinking the suspension could cause some timing issues. Is the center driver blind? Perhaps the front and center drivers could have extremely hard suspensions to help minimize the chance of issues.

Asteamhead
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Re: Main crank pin on different axle then Eccentric on

Post by Asteamhead » Mon Oct 15, 2018 11:55 am

No problem at all.
Look, many 3-cylinder engines had their valve excentrics and their middle cylinders at different axles. No issues, no further measures necessary.
Asteamhead

Kimball McGinley
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Re: Main crank pin on different axle then Eccentric on

Post by Kimball McGinley » Mon Oct 15, 2018 2:29 pm

The Marie Estelle and E have springs as optional; one axle is solid-mounted and one just has a center pivot. This makes a classic 3-point suspension. I built mine as- designed, the solid rear axle goes right through the ashpan. The front pivoting axle does carry the eccentrics. I considered switching them for stable valve events, but the ashpan side would have needed big slots in them.

skyloop440
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Re: Main crank pin on different axle then Eccentric on

Post by skyloop440 » Thu Mar 14, 2019 1:35 pm

I don't see any reason this would not work just fine, specially since the second and third drivers are solid linked. if you think about it even if the eccentrics were on the third axle the valve gear is designed off of a single point, when that axle moves up or down it throws the timing off just a little anyway so moving it forward one axle would only do the same and for the split second that it does this I don't think you would even notice it.

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johnpenn74
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Re: Main crank pin on different axle then Eccentric on

Post by johnpenn74 » Sat Mar 16, 2019 5:58 pm

Well, Duh.... how is it on the prototype? If you are going to build a model of 42, put the eccentrics where they go. More specifically, use the Milner design as a guide not a rule. You are changing the main rod remember? :-)

JP
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