Crankshaft install...to tight?

[jzearfoss]

I am in the process of installing the crankshaft in my 1968 280 SL. I have gone through the initial torque sequence using plastigage and the main journals have come within spec. Six out of the seven come in at .002 in. and the seventh is at .0015.  (A bit out but not bad) That one is main No. 7 at the rear of the crankshaft.  These measurements were completed with the crankshaft and bearings dry. 

I wanted to check to see how well the crankshaft would rotate when lubricated so I reinstalled using a lightweight oil (automatic transmission fluid) and torqued to spec. (58 ft. lb.)  Here is my result.  The crankshaft rotates smoothly, (i.e. goes through 360 degrees with no hiccups) but it does rotate freely.  That is, I have to apply constant rotational pressure on the crankshaft to keep it rotating.  It will not freewheel.

Here is my question.  Is this to tight?  Should the crankshaft freewheel?  i.e. spin on its own without applying constant rotational pressure?

[ja17]

Do you have the rear main seal in place and have you checked the thrust bearing flange clearance?

[jzearfoss]

Yes - the main seal is in and the thrust bearing is in and end play is okay. another bit of info - rechecked torque specs and discovered that that main bearing torque for the 280 engine is 65 ft. lb.  I have retorqued the mains and still have the same condition.  Crankshaft turns smoothly with constant rotational pressure but does not freewheel.  jz

[Benz Dr.]

Yes - the main seal is in and the thrust bearing is in and end play is okay. another bit of info - rechecked torque specs and discovered that that main bearing torque for the 280 engine is 65 ft. lb.  I have retorqued the mains and still have the same condition.  Crankshaft turns smoothly with constant rotational pressure but does not freewheel.  jz

And it won't.

[wwheeler]

I would think with the new seal installed, it will never free wheel. That is a rope seal and not what I would call a low friction oil seal. It it free wheeled with the seal, you would have a rear main leak.

[ja17]

Yep, you will get some turning resistance with the rear main seal installed.

[jzearfoss]

I had a slight suspicion that might be the case but it did not make sense to me since it was only half of the seal that is in contact with the crankshaft. I would think that one way to confirm that possibility would be to install the crankshaft and torque down the mains without having that half of the rear main seal in.  (I am not going to do that...yet)

Since it does rotate smoothly I am going to continue and install the oil pump, timing chain, and lower pan and then install the cylinder head.  I am curious to see if the added resistance from the valve springs will make a difference in the rotational condition that currently exists.

[wwheeler]

There is a very specific technique to installing this rope seal. I can't find the procedure at the moment and is in the service books. Maybe someone has it handy? Basically says to pack the seal in the cavity using a rounded bar about the same diameter as the crank main. Then making sure it is completely seated. Then cutting the ends but leaving a short stub (.6mm???). Same goes for the lower half. When the two halves come together, the extended ends compress, forming a tight seal. Might confirm that.

But yes, just having the upper half should have some effect. But if not packed all the way in the cavity, the rope seal may create more than normal drag. If you followed the procedure, you should be ok.

[jzearfoss]

Hey wwheeler - I am up to speed on the install of the rear oil seal.  Tapped it in with a wooden dowel as recommended and left the 0.6 mm above the deck of the block.  One thing of note is that once you do that and then torque down all the mains on the crankshaft you produce a lot more pressure on the oil seal and it seats even deeper into the recess that holds it in place.  At least that is what happened to me.

The first time I did this it sank below the level of the deck.  I pulled the crankshaft and repeated the whole process again (with a new piece of oil seal) but this time I left a whole lot more of the seal above the deck.  I reinstalled the crankshaft and torqued down all the mains and after doing this I pulled the crankshaft and then trimmed the oil seal to the 0.6 mm. (tough stuff - I used a Dremel cutoff wheel to trim)

Reinstalled the crankshaft and torqued to spec and the oil seal maintained the 0.6mm protrusion.  Love learning this stuff.  Need a lot of patience and willingness to do things two or three times in order to get things right.

[ja17]

Rope seals are ancient technology. They are not exact science by any means. Over the years the manufacturing materials for rope seals have changed and so has the installation specifications. In addition, the area on the crankshaft that the seal contacts is "reverse knurled" from the factory. The finely machined knurling is oriented to sling oil back inside the oil pan as the crankshaft rotates. The constant contact of the rope seal on the "reverse knurling" causes the knurling to disappear or becomes much smoother over time, reducing the effectiveness of the whole rope seal concept. These days it is tough to get the rope seal working perfectly.