Brass loco throws traction tire... Thoughts?

[nstars]

Sorry, I should have been clear, it's for the 2012 addendum, not published yet and it's part of a 3 project article about K4's. Two of those projects concerns plastic K4's (like the one for Doug Nelson), but the last project concerns upgrading of the PSC K4's. Brass loco's are indeed not normal for the addendum, but these PSC K4's have become quite numerous and not too expensive. As part of a complete article with lots of plastic, the brass upgrade was 'acceptable'.

Marc

[mmagliaro]

I reread the thread, Dave, but must have missed something.  Did you put BFS on *another* driver other than the center one, with the intent of getting your traction back from a different wheel other than the middle one?  Is there BFS on the center AND another driver now?

[Dave V]

I reread the thread, Dave, but must have missed something.  Did you put BFS on *another* driver other than the center one, with the intent of getting your traction back from a different wheel other than the middle one?  Is there BFS on the center AND another driver now?

Yes.  What was happening was I couldn't apply a thick enough BFS layer to fill the groove (and still be relatively smooth), and so I still was losing traction.  So, in desperation, I snotted the third driver, same side as well.  She runs fin with minimal stalling, but now I'm tempted to revisit.  The BFS on the center driver has had two days plus to cure; I may be able to put another layer on the center and strip the third drive back to bare so as to restore full pickup.

[mmagliaro]

I happen to have a full set of those PSC K4 drivers, and the center driver with the traction tire definitely has a threaded crankpin hole.  I just checked.
So the crankpin *should* screw out, but as Victor points out, you'd have to turn the eccentric
arm around and around with it, which means moving the wheel, etc.

And getting all that back together so the crankarm ends up in the right spot is hard.
Unsoldering from the pin is easier.

[Dave V]

Awesome, thanks Max!  Hopefully BFS will be my answer, but it's nice to know long-term that it can be done.

[nstars]

I made a quick check and it is indeed possible to unscrew the crank pin. This is the way Hans replaces the traction tires. You have to turn counterclock wise. For replacement tires you could use Concor 4-8-4 tires.

Marc
 

[peteski]

I happen to have a full set of those PSC K4 drivers, and the center driver with the traction tire definitely has a threaded crankpin hole.  I just checked.
So the crankpin *should* screw out, but as Victor points out, you'd have to turn the eccentric
arm around and around with it, which means moving the wheel, etc.

And getting all that back together so the crankarm ends up in the right spot is hard.
Unsoldering from the pin is easier.

In theory, the eccentric arm should end up in its original location (since the crank pin should be tightly seated in the same location as before removing it).  If not, then use some thread locking compound to lock it in the appropriate position.  Basically, what Victor said.

[mmagliaro]

In theory, the eccentric arm should end up in its original location (since the crank pin should be tightly seated in the same location as before removing it).  If not, then use some thread locking compound to lock it in the appropriate position.  Basically, what Victor said.

Yes, in theory.  Heh.  I don't think I would count on that.  However, if you just remember where it was when you started unscrewing it, yes, you should be able to just put it back there, and if it won't stay because it loosens up after being unscrewed, ... yep, Loctite to the rescue.  (although maybe
just some ACC or something, if it holds and you want to be able to get it out again)

Marc, Hans:  Just how hard do you have to turn to get it to come out, and is it safe to grab it by the eccentric arm, or did you grip the actual pin with very tiny pliers?

[peteski]

Yes, in theory.  Heh.  I don't think I would count on that.  However, if you just remember where it was when you started unscrewing it, yes, you should be able to just put it back there, and if it won't stay because it loosens up after being unscrewed, ... yep, Loctite to the rescue.  (although maybe
just some ACC or something, if it holds and you want to be able to get it out again)

That is what I don't understand. The thread is a single grove in metal. No matter what you do, the crank pin will thread into the hole in the same exact place it was in originally.  Unless you jam it in and cross thread it.    Since the crank pin will screw back in only one way, it should tighten at the same exact spot where it was originally tightened.

[victor miranda]

hi peteski,

yeah that is the theory...
I am not at all sure the why of this observation:
I have tried to tighten a few main cranks back into place and
the eccentric does not stop where it needs to be.

I suspect the main crank is glued to the driver and
the person assembling turns it to snug.   
once the glue is out, the main can turn more
.... thereby miss-placing the eccentric.
any other guesses are valid.

If the main crank is NOT loose, I advise to leave the worms in the can.
You will have to solder either way...
ETA: check that... red loctite can allow you to escape the soldering.
  you need to disassemble to lubricate it anyway, right?


victor

[mmagliaro]

That is what I don't understand. The thread is a single grove in metal. No matter what you do, the crank pin will thread into the hole in the same exact place it was in originally.  Unless you jam it in and cross thread it.    Since the crank pin will screw back in only one way, it should tighten at the same exact spot where it was originally tightened.

That all depends on how hard the metal is an how hard you push when you put it back in.   Haven't you taken a screw out and put it back in a few times, only to find that it just isn't tight any more at the exact spot where it used to be, and you have to turn it, perhaps 1/4 turn more to make it tight?    It's not quite "stripping" the threads, but they get deformed a little.

I agree, the metal on this thing is probably sturdy, so it should not be a problem.

[Chris333]

Take a pic before you take it apart 

[Dave V]

For the time being, I probably won't have to take it apart...   

[John]

Dave .. not being a steam head, can you post a couple of pictures of the problem area?

[Dave V]

Dave .. not being a steam head, can you post a couple of pictures of the problem area?

Maybe later...  For now I don't really have an issue now that the BFS cured.