Plenty of cars have have a one piece pulley/damper/balancer arrangement where the pulley is bonded along its inner circumference. With that design, it is indeed possible for the pulley portion to "disconnect" and spin independently of the crankshaft. But the engine in question is of a significantly different design. A failure comparable to that of your father's Lexus is not possible.

So I got a little fresh with the cap screws and they all came out. None were broken. The belts are all off and at this point, the balancer has a lot of play in it. It spins and wobbles.
I'm having some trouble getting the 27mm headed bolt off. I tried the method suggested above (shoring up the breaker bar and hitting the starter) but I need to get a helper to hit the starter so I can see what's going on. The nut seems to be moving when the starter turns the motor so that's encouraging in so much as the crank doesn't seem to be broken. The slots for the pins may be another story.
Ok, breaks over.

I want to be sure that future readers of this thread understand that there is a rubber part that can fail on the vibration damper. If it fails, a metal portion of the vibration damper can disconnect and can flail around outside the pulley's.
This does not mean that the pulley's are loose or that the harmonic balancer is loose on the crankshaft. In the thread that I linked, such a failure occurred and the original poster was mislead by advice indicating it was a failure of the pulley or balancer that needed immediate repair. He drove it quite a ways with a separated vibration damper and did no further damage.

Update...
Got the "vibration damper" and "balancing disc" off. The two steel pins were sheered lengthwise. The pieces remaining in the balancer were intact and I used a center punch to drive them out. The other half of the pin was broken into small pieces.
The groves in the crankshaft look good. I used the piece from the balancer to check the fit on the crank and it looks good. I think I got really luck here.
While I've got everything apart, I'm planning to do the following preventive maintenance:
new cap screws
new main bolt and cup springs
All new belts (hoses are in good shape)
replace water pump
thermostat
front main seal and spacer
AC compressor (has a leak)
I was thinking about the alternator but I'm going to wait on that for now
Any other things I should take care while I'm in this deep?
By the way, I didn't find a rubber spacer when I took things apart. I've got the parts soaking now and I plan to have a closer look later.
Thanks for all the help.

James, you need to buy a lottery ticket today. Do you have any idea what caused the dowel pins to shear? Seems like it would require a lot of force.
If you click on the thread I linked earlier, it shows the vibration damper which has a rubber component.
Were you able to get the 27 mm bolt out using the starter?

Reinstalling the pins will only work if the keyways are not wallowed out. If they look good the installation of the dowell pins is a tricky process. If it is not done exactly correctly the keyways will be damaged and a new crank is the only true and permanent fix.

Tom W

I removed a "balancer" you talk about, held by the two pins on the snout, from an OM617 engine I was dismantling yesterday. I'm surprised those pins can shear like that. It took quite a bit of force to remove it from the crank with a puller.

Yes, I am thinking it was probably not installed correctly allowing it to wiggle enough to destroy them. In which case the keyways are probably wallowed out.

Oh, BTW wallow is a term referencing hogs wallowing in the mud, for any city folks not getting the meaning.:)

Tom W

Thanks, but us city folks have been watching the presidential primaries, so we understand. :D

Pictures?
 

Pictures, pictures, we all need pictures.

Did the balancing disc slide off easily?

The balancer came off pretty easily. I didn't need to use a puller. There was a lot of front to rear movement and I just gave it a nudge with a socket extension to get it the rest of the way off.
As for a reason for the failure, I'm thinking the big bolt wasn't tightened to proper torque or the cup spring flattened out and the bolt loosened up. The cup springs look more like flat washers.
I've got some pics but I need to resize them to post them.

Then you probably need a new balancer. Hopefully, the balancer took the hit and not the crankshaft.

http://i52.photobucket.com/albums/g1...tiondamper.jpg


Vibration Damper. No Rubber part between damper and balancer unless the black gunk is all that's left of it.
http://i52.photobucket.com/albums/g1...SheeredPin.jpg

Sheered Pin. The halves that were still in the balancer.

http://i52.photobucket.com/albums/g1...cranksnout.jpg
CrankShaft Snout. The edges of the groove look sharp but you can see some wear from the broken parts. I have no idea what the goo is on the upper left of the housing. Maybe gasket silicone from a previous repair? Any ideas?
http://i52.photobucket.com/albums/g1...cingdisc-2.jpg

Balancer. The grooves look sharp.
http://i52.photobucket.com/albums/g1...cupsprings.jpg

Cup Springs, cap screws and the big bold (18mm dia, 27mm head). I haven't cleaned them. Note, no washers on the cap screw. Manual states they stopped putting washers on them Jan 1979.

Let me know your opinions on the grooves in the crank and balancer. Do they look ok? Or should I start looking for a rebuild engine?
If the crank needs to be replaced, I would lean toward doing a rebuild.
http://http://i52.photobucket.com/al...tiondamper.jpg

All grooves look ok to me. I'll be curious to know what other people who have worked on these components have to to say.
Can't figure out if your balancer is the same as the one pictured in the thread I linked on which the rubber separated.