N Scale Intermountain AC-12

[peteski]

On some models the main crank (and eccentric)  is keyed (like square shape or round with a flat spot) to keep it properly aligned. But in many locos it is simply round and it depends on the tight fit for staying in proper alignment.  There really should be very little load in the eccentric so it should not readily get out of alignment (even if the crank is  round and press-fit).  The eccentric only drives a very fine rod which is purely cosmetic and should present no resistance at all.

[victor miranda]

lets not retire the model yet....

I think worn out brushes may be the better time.

I am going to have to look at my ac-12...
I have no idea what holds the eccentric cranks in place.

once you have a little practice looking at quartering, it is pretty easy to see problems.

after that things can get a little bit problematic. 
as an example, when you see the quartering in a model power pacific has gone askew
it is often the driver has cracked.  this is very difficult to fix.
one is better off replacing the axle set.

find the problem driver/axle first... then we find a fix.

victor

[carlso]

Peteski - I see there is no "load" upon the crank, but it is moving on the crank pin and I don't think it should. It looks like the head of the pin was squre with the crank pressed on, however it looks like the crank has looseened and shifted back and forth enough to begin rounding the pin head.

Victor - I am Scotch Irish and bull headed as, I'll be nice here, heck, so I won't shelve it even if motor fails. I would get great pleasure in trying to figure out a way to put a coreless motor in it. The problem with this IM AC is I doubt very seriously if they have replacement drivers. They have not indicated that they do because I did order some. Oh, wait a minute, I better finish my GS-4 re-motor project before I tackle anymore like that. Just waiting on NWSL to send parts I ordered.

Once I get the rear crank pin set where the loco runs smooth, without the bouncing 3rd axle, I think I will put a very thin coat of epoxy on the crank and the pin head as a temporary fix. Since I have new ones coming I will not be out much if the epoxy doesn't work.

Carl

[peteski]

Peteski - I see there is no "load" upon the crank, but it is moving on the crank pin and I don't think it should. It looks like the head of the pin was squre with the crank pressed on, however it looks like the crank has looseened and shifted back and forth enough to begin rounding the pin head.

Yes, you're right, the eccentric should be permananty attached to the crank pin.

The problem with this IM AC is I doubt very seriously if they have replacement drivers. They have not indicated that they do because I did order some.

Why not try find out for certain?  Email and call them directly and ask.

Once I get the rear crank pin set where the loco runs smooth, without the bouncing 3rd axle, I think I will put a very thin coat of epoxy on the crank and the pin head as a temporary fix. Since I have new ones coming I will not be out much if the epoxy doesn't work.

Sounds like a plan to me.

[victor miranda]

take my word for it... it is possible to run an n-scale loco to death.

I did in a minitrix 0-6-0
the axle bearings were cut deeply into the chassis
and the gears all were pointy. 
I forget how many times I replaced the brushes...

back to your loco.

if the eccentric is loose. green loc-tite may be a good way to reattach it.
I can't figure out how the thing is attached.
it looks like a hexhead screw is embedded in the crank....

in which case pull the main pin out and tighten the thing.
.... skip the glue.  or use medium loc-tite.

damn that motor must have a lot of torque available.

victor

[peteski]

damn that motor must have a lot of torque available.

victor

Maybe the motro has more torque than all the other similar motors, but the relatively high gear ratio(which you mentioned in your A-board writeup) is what results in lots of extra torque at the drivers.

[mmagliaro]

You've covered all the main points already, gentlemen. 

My quick notes. 

I immediately saw the out-of-position eccentric on the front engine whacking the valve slider, so I'm glad you
corrected that.
Yes, if the crank is loose on the pin, or the pin can move in its hole, that needs to be fixed.  There isn't much
load on it, as Peteski pointed out, so a bit of epoxy or Loctite will probably do fine there.

As for motors...  It may interest you to know that when we were doing torque experiments, I called up Intermountain
and bought an AC12 motor because Victor thought I might be interested in its performance.  It was very inexpensive,
but took a month to arrive, and they only ship used ones.  They have no new ones.  But they will
test it and make sure it works before they send it to you.  So if your motor dies, there is a remedy available.

As for drivers, I see so much play in so many of the drivers that it's hard for me to actually tell what's wrong.

[carlso]

Thanks to all. I have attached a couple of images that shows as Victor suggested a hex head on the pin with the crank just pressed on. I attempted to lift off the crank only but found the entire pin coming out so I pushed it back on and I heard a click as if it snapped into the hole. I will wait for my new parts to come in before going any farther with the pins. I should have all new rods, pins, valve gear, cranks.

To show how that one crank is swiveling on the pin I have two images. The first one is how the thing was in my video with the crank rod slamming into the cross head guide. I looked at that video so many times and was not smart enough to pick up on that. I did think it was strange how that rear engine crank rod had way more action then the one on #1 engine. Thanks Loren.

Second image shows how far to the right I can swivel the crank, and in fact it appears to be about where it should be. You can see the head of the pin and indeed it looks to be or was a hex head. I think I will gently file the top of the head and crank, clean with alky and put a very thin layer of epoxy as a temporary fix. BTW, neither of the other 3 cranks show this problem.

The way she was ...................



The way she should be ? ? ? ...................



The crank may be a tad too far to the right. If I move it ever so slightly to the left it should then line up with the mid point of the counterbalance weight.

Max, I agree about the play in the drivers. I can not remember if they were that way when new or if that has come from extensive running. Maybe a little of both. Maybe IM did that, even though it is articulated, to make it run on tighter radii. Who knows, it has been a good performer in the past and shall be again.

Thanks to all for looking and helping a dufus,

Carl

[mmagliaro]

Carl,
From those two photos, it looks like the pin is turning in the hole in the driver, rather than the crank turning about
the pin itself.   There is a little divot into one of the 6 sides of the pin that clearly rotates clockwise
from one photo to the next.

 Either way, if it were my engine, I would probably just put a drop of epoxy in both places and be done with it.
There isn't much pressure on the eccentric/pin joint.    But the rods do push and pull on the pin inserted in the driver,
so you need a tight fit there, and it looks to me like that pin is moving in that hole.   New pins are worth a try if they
are coming to you from IM, but I think you may end up having to epoxy that pin into that hole to get it to stay.

There are more drastic measures... let's hope that a bit of Loctite or epoxy in the hole stops the pin from rotating.

[carlso]

Max,

good eye, good catch with seeing that divot. I agree the pin is rotating as you suggest. I think I shall set it aside until my parts come in. I don't want to epoxy the pin and then not be able to remove it. Would the green loctite allow the pin to be pulled or would it be as difficult as the epoxy?

Carl

[mmagliaro]

Max,

good eye, good catch with seeing that divot. I agree the pin is rotating as you suggest. I think I shall set it aside until my parts come in. I don't want to epoxy the pin and then not be able to remove it. Would the green loctite allow the pin to be pulled or would it be as difficult as the epoxy?

Carl

Loctite in a plastic-to-metal joint is never all that strong, like it is with metal-to-metal.   I would be inclined to
try it, or even ACC first, because those would probably still let go pretty easily if you had to pry that pin out.
JB Weld, well, that depends on what that plastic is.  If it's Delrin or some other such slippery engineering plastic,
even JB Weld doesn't hold al that great.  But if it's any other kind of plastic, it could be a bear to get out.  I would
trying conservative methods first:  1. New crankpin  2. Acc or LocTite  3. Epoxy if necessary

If it keeps letting go with epoxy, then you are down to much more "invasive" methods, like filling the hole
with heat melted plastic and redrilling it, or using a sharp #11 blade to cut a series of little slits into
the inside wall of the hole, then fill it with JB Weld, let it get rock hard, then redrill it for the pin.
(the slits let the epoxy grip in there like "fingers" so even if it can't stick to the Delrin, it will still stay put.

These latter ideas are extreme measures.  I suggest trying the conservative things first.