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Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 9:09 am
by Dale_F
I am helping a friend with his Allen Mogul and the problem we are currently addressing is a very stiff throttle. The Mogul has a dome throttle with a packing nut on the back head. I am wondering if it could be just the packing nut, or if there could be something going on with the throttle in the dome. I hate to open the boiler unless it is really called for. The drawings for this locomotive have long ago been lost, so I am looking for help here.


Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 10:06 am
Is the problem while under steam or cold? The throttle on my Shay is very stiff when cold.

John B.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 10:13 am
by Dale_F
The throttle is stiff when under steam. I tend to "jump" the locomotive when trying to start because the throttle is hard to pull so little, fine adjustments are hard. My Atlantic has a smokebox ball valve which is smooth and where I can do very fine adjustments. This is just a lot harder to do little adjustments. Maybe it is the packing gland. I am pretty sure it is graphite string, but that is just a guess.

The packing nut appears to be a compression fitting with the brass "ring" being replaced with string. It works well, as far as not leaking steam. I just wish it were easier to open and close.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 10:40 am
by cbrew
Morning Dale, my Allen boiler was the same way before i went with a ball valve smoke box.
what i found is the arm on the stock Allen throttle design was binding on the trunnion caused by the spring that pushed the valve disk to the body.
if i was to do this again, I would follow what Don Orr did in the Tail of the five moguls write up he did in Live Steam a number of years ago.
In short, he replaced the Allen valve assembly with a steam rated ball valve in the dome.

I guess the main reason i have not done this, i was/am worried about removing the dry pipe assembly after 14 years of service. not sure if the cap screws will break lose or just break :D :) 8) :?

while the smoke box throttle works, I have burned a few up.

so in short, you may need to pop the dome off and look closer at the valve body.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 10:43 am
by NP317
Try lubricating the throttle rod at the packing nut first.
If that doesn't help, then remove the packing nut (when the boiler is cold!) and see if the throttle loosens up.
That's the easiest problem to resolve. You may need to repack it.

I have an Ed Perry-built boiler for my Allen Ten Wheeler and the dome easily is removed to check the stock slide throttle.
Just be patient removing/tightening the bolts in a pattern, as you would do with an engine's valve head, to equalize stresses.
And put a position mark on the dome so it is returned to its original location.

Let us know what you find.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 11:25 am
by Dale_F
Thanks to both Brew and RN for the help. I will pull the packing nut and hope that helps. Otherwise, armed with your information, I will open the steam dome! I will update my progress here.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 4:16 pm
by Rwilliams
Last several years I have gone through more full size globe valves and injectors on full size locomotives than I can count. First thing I discovered is that the guys who worked on the valves before me often compromised various elements of their rebuild. I have found wire reinforced packing that ate up the stem as the packing was tightened down over time. The stems where the packing makes contact was often poorly finished leaving an almost thread like condition that made for rough operation and shortened packing life expectancy. Lots of leaks as the rough stem surface ate into the packing on a regular basis. Lack of a good high temperature anti-seize type of lube mixed in with the packing to provide some extra lubrication over the long term is also a wise move. Best of all is to polish the stem where it passes through the packing to a glass smooth surface to insure the smoothest operation possible. I can see where the same attention to detail on model boiler throttle valves would be in the best interest of smooth operation.

With the workmanship of the original builder unknown, just taking things apart and making a critical inspection might be for the best to insure all is well where most do not want to venture unless necessary. No telling what you might find. I have learned to not trust my predecessors who were supposedly well trained steam mechanics. I have learned that their work is not to be trusted. Often times their philosophy was that if the repair makes it for another trip, it is good forever.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 5:12 pm
by Bill Shields
Lots of good advice.

Other suggestions - are the sliding surfaces bronze / brass or STAINLESS?

Simply changing material from stainless to bronze can help

if you are not in a position to put in a smokebox throttle (which can be a bear after the loco is built), you can replace the pull / slide throttle with a screw throttle or inline plug type of throttle - > and use the same pipe / rod arrangement.

I can provide some drawings / pictures if you like.

Either way, it is a lot of work to change the throttle.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 9:30 pm
by Steve Alley
Yes most differently lube the throttle shaft. Seen it been there. Packing get crusted and lube it cold, steam oil on the packing is best. Need to unscrew packing gland or nut and drip on steam oil. It last the longest. If its graphite packing. Need to loosen up and repack.

Re: Stiff throttle on Allen Mogul

Posted: Mon Apr 02, 2018 10:36 pm
by blff cty lcmtv wrks
i have built five of the allen dome throttles and i had the same problem that you have. i modified the throttle lever and the throttle lever pin a bit. i made a bushing out of stainless steel about a half inch long. it was 3/8 inch od by 1/4 inch id. this was silver soldered to the throttle lever in the proper location. the stainless steel lever pin was modified, likewise. the theory being that it would have a bit more bearing surface, and would resist the force of the spring as it tries to twist, sideways, the lever what holds the disc up to the throttle body.
respectfully submitted
big c
bluff city locomotive works

Re: Stiff throttle on Allen Mogul

Posted: Wed Apr 04, 2018 12:32 pm
by Dale_F
All those who suggested to repack and lubricate the throttle rod have won the "door prize", which is my Thank You!

I pulled the packing nut off and the throttle was smooth and easy, so I cleaned all the old packing out, rewrapped with graphite and added a drop of steam oil on the shaft. It worked like it is supposed to -- and best news is I did not have to open the boiler because we all know if you open the boiler, then all the magic can leak out and it will never work right again!

Thanks to all.

Re: Stiff throttle on Allen Mogul

Posted: Thu Apr 05, 2018 9:52 am
by NP317
Well done!
Seek the simple answer first. A good rule for life.
And steam.