I will very soon have to replace the front seal on my 1974 - 300D turbo 123 . Are there any secrets I should know about before starting this job. What about pulling the balance wheel assy. Any tips for this. Thanks
John Winter

You have a 1974 300D Turbo?????

Anyway, there certainly is a trick to this job. As far as replacing the seal, it's not too different than any other front crankshaft seal job in most engines.

Where the difference comes in is how to get the balancer back in place properly and without destroying the crankshaft. Most engines have a square keyway with half the square groove in the balancer and half in the crank and a square key to pin them in position.

On the 616/617 engines, that I expect you have, there are two round pins 180 degrees apart. These pins fit in holes that are half in the crank and half in the balancer. To get the balancer back on, you need to clean the crank snout and the balancer very thoroughly seeing that there are no burrs or anything.

Put the balancer in position a little counter clockwise of the position where it looks like the holes will align. This is because when you start tightening the bolt, it will turn slightly as you tighten down. If you get it right it will turn into proper alignment for the two steel pins. If it does not align, use your harmonic balancer puller to pull it off and try again. Repeat this until you have proper alignment and the pins fit easily in place.

Many of these engines have been ruined by unknowing people that simply slam the balancer on the crankshaft and then use an impact wrench to drive the balancer in place. On most cars with a square key this works reasonably well as long as you start and align the key first. But this approach is nearly certain death for your crankshaft and will strand you beside the road at some point.

Proceed carefully and take whatever time necessary. If you don't you will be sorry.

Hope this helps,

No, I have a 1974 240D and a 1984 300D turbo.
Thanks for the inside tip on the two pins. At what point can the pins be reinserted into their holes and how hard are to press in, big hammed or very small hammer.
Thanks John Winter

As I described, you will most likely put on and pull off the damper several times before getting the holes aligned. Once the holes are aligned, you should be able to tap the pins in place with a small hammer. The very end of the pin is slightly tapered, so if the holes are closely aligned, the pin will move it the last 1 or 2 thousandths of an inch. If you tap them in with a hammer without the pin trying to cock sideways, it is adequately aligned.

Once the pins ARE aligned, tighten the crankshaft bolt and TIGHT. I don't remember the exact torque but it is SIGNIFICANT. Something like 150 Ft Lbs or more.

Good luck,

As I described, you will most likely put on and pull off the damper several times before getting the holes aligned. Once the holes are aligned, you should be able to tap the pins in place with a small hammer. The very end of the pin is slightly tapered, so if the holes are closely aligned, the pin will move it the last 1 or 2 thousandths of an inch. If you tap them in with a hammer without the pin trying to cock sideways, it is adequately aligned.

Once the pins ARE aligned, tighten the crankshaft bolt and TIGHT. I don't remember the exact torque but it is SIGNIFICANT. Something like 200 Ft Lbs or more.

Good luck,