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Discussion Starter · #1 ·
Hello All,
I am wondering if anyone knows the piston size of the Accucraft Mogul (first generation with the gas tank in the cab). I am getting tons of blow-by on my cylinders, so I am going to replace the piston rings. However, I do not want to take it apart twice, once to measure the piston and once to replace to rings. So if anyone knows the size, that'd be very helpful. Thank you!
 

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Hi, I have a mogul same as yours that had steam leaks but I found they were from valve spindle glands so I undid the gland nut and wound a small strand of teflon tape around the shaft then re-tightened the nut that gave some crush to the existing o ring and the new teflon. Then I backed it off an 1/10th of a turn.
If its the piston rings, from my poor notes from a while ago I think the OD is 14.28mm and ID is 1.32mm ( sorry I only work in metric) . I have notes on the other Accucraft piston size of 15.71mm OD and 12.91mm ID but I think these are on the bigger Consolodations and Mikado's and the Mogul has the smaller cylinders but I may be wrong so please can someone correct me if I am wrong.
Hope this helps
Russell
 

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Discussion Starter · #3 ·
Hi Russell,


I should be a little more clear. I am not getting blow by on the packing for the piston rod itself. The piston is tight, however if the engine stalls, it is pissing steam out the stack, which means it is blowing past the piston and through the exhaust port. Thanks again for looking at your notes. If anyone knows the piston size or the o-ring size for the piston in particular, that info would still be much appreciated!


Trevor
 

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Trevor, does this loco have piston valves with a piston valve reverser ?. If it does then what you are seeing is normal. The steam feed to the piston valves is reversed by the reversing valve from inside to outside admission. This requires 100 % admission. This means there is always a path for the steam to travel through the valves leading to what appears to be "blow through".

DougieL
 

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I believe Accucraft uses 1/2" & 5/8" pistons. If I were to guess, I would say 1/2" but you can get them delivered from McMaster in a few days so I would pull the pistons first and check it out. If it barely runs, it could be that the piston has come off the piston rod. I believe you can easily remove the piston by pulling the front cap and unscrewing the piston rod from the crosshead.
If it is only one piston, you can tell which one it is when it stalls the bad side will be half way through the stroke with the wheel crank pin at 6 or 12 o'clock. Pull that one first.
A quick fix that Dave Hottmann used to use is to cut strips of a dollar bill and wrap them under the o-ring. about two thick. Teflon tape does the same thing
 

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I believe the Mogul has 9/16" bore cylinders. The o-rings can be either metric or imperial sizing. Best to pull the piston out and see what you have to start with. It is four bolts and unscrewing the piston from the crosshead (and locking nut) as Bill mentioned above.
 
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