MTH PS2-3v Shay Slipping Drive Shaft

If it's just the shaft slipping, something like Loctite 660 retaining compound might be the answer.

I believe the gear on the crankshaft is pressed on. It may or not be slipping but you have pull off the covers to inspect the other gears. Some may be worn. MTH has a few of these parts but I had to rebuilt one gear with a new sleeve as it had worn out and barely making contact with its mating gear.

With a few new gears now.

Pete

I actually checked those gears out. They're fine, especially now that they've been re-greased.

The issue lies where I've drawn the blue arrows. That doesn't seem to be holding anymore.

I’ve seen the crank shaft break on a Shay, but I haven’t seen the gear attached to the crank shaft slip……is it that gear on the crank that you see slipping? ….more common failure is the parts Pete pointed out.

Pat

All the gears are fine. It seems to be that the shaft with the gear on it is slipping out of the cranks. The gear itself is still firmly attached to shaft.
A few observations  I've noticed when using on rollers. When running forwards, the shaft worms its way out of the rear cylinder pins. The front geared truck continues to run but the rear three do not. The opposite occurs when running in reverse. Applying downward pressure causes the shaft to spin out of both.

Is there a set screw on the crank arms where they attach to the crankshaft?

Or... I wonder if one of the pistons are hanging up in a cylinder?

I want to say the crank shaft is multiple pieces….split where the gear is on the crank shaft,….it’s possible the two crank shaft halves have lost their friction fit, and one half is spinning with the gear, and the other half is slipping,…..if that’s the case, it’s very repairable,…just a lot of work,…..the 3 cylinder engine is available as an assembly at mthpartsandsales.com

Pat

@harmonyards posted:

"it’s possible the two crank shaft halves have lost their friction fit, and one half is spinning with the gear, and the other half is slipping"

This!!

I've seen the part on MTH, but I'm curious if there is a solution that doesn't require me to drop $130 on it.
John's Loctite 660 seems like something that could work, if the solution is used sparingly (and I mean sparingly.)

Might also look at the companion flange on the end of the crank shaft ( each end ) as Ryan points out, ….see if the universal joint companion flange is loose??……I think it’s pinned to the end of the crank shaft, …or might be a set screw?……

Pat

@BBasalik posted:

This!!

I've seen the part on MTH, but I'm curious if there is a solution that doesn't require me to drop $130 on it.
John's Loctite 660 seems like something that could work, if the solution is used sparingly (and I mean sparingly.)

I’d confirm the condition by observing the crankshaft’s rotation first. Do you see 1 or more of the crank shaft’s throws stop rotating, but the other end of the crank shaft  (the geared portion) continue to turn?

Pat

If looking at the set of three cylinders, when the problem occurs going forward, the rear two cylinders stop actuating along with the geared wheels. The front cylinder and front set of gear wheels continue to turn. The opposite occurs in reverse.

Looking at the entire crankshaft, the universal joints are held on the crankshaft with set screws. These are quite firm and have no slippage.
The gear and its associated axle seem to spin out of the bearing at the end of piston bearing. There are no screws on this end. It appears to be pure friction that holds these in place. I can actually push the geared axle back into the piston bearing (with effort) and the problem is resolved. It just re-occurs after a little bit of drive time.

Now for the repair,…..first, and forgive me, it’s loaded, I know, but I work for MTH parts, and I can tell you with we waited quite a while to get a run of spare Shay parts back on the shelf to keep those older machines alive….So I’d suggest stocking up on known failure components, like the traversing gears, couplings, idler gears, and the engine itself…( 3 cylinder steam engine assembly) …..if you love your Shay, you’ll thank me later…….now, to get a sturdy fix, you’ll need to remove the 3 cylinder engine, and carefully take it apart, to extract the crankshaft itself from the cradle. ….yes, it’s a lot of work, but you want to be able to split that crank shaft, and get it clean, clean, clean, before you attempt to use sleeve retaining compound,…….personally, I prefer loctite 640, or Permetex equivalent 64040, as it has a superior gap filling quality, and is stronger than 660, 680, etc,…..probably no harm or foul with either, but that’s my preference. Clean all parts, apply the retaining compound to both parts, and press back together.  Timing of the crankshaft orientation doesn’t matter, so don’t worry about it,…..allow the crankshaft to sit overnight, and reassemble your engine, lubricating every moving part as you proceed. It’s tricky, and a real clock bandit, but can be fixed….

Pat