The rubber you see is on the outside. How do you know the rubber on the inside ( the other 95 persent ) is bad ?
If the timing marks and outer ring has not moved leave it alone. You will be opening a can of worms.

The rubber being visibly bad is a problem beyond whay many may expect. Not only can the timing mark "regress", the outer ring could seperate while you are driving, and this has in fact been responsible for fatal accidents when it manages to bounce across the road into on coming traffic. Granted you are talking about some very unlikely set of circumstances, but I know of two incidents in the last ten years where a lost damper made it through someones windshield, and stuck an occupant causing fatal injuries.

As far as replacing it goes, it's easy. To remove the bolt, get a breaker bar, the correct sized socket and a pipe. Wedge the bar against the floor so that when the starter gets engaged, torque from the starter will be resisted by the breaker bar and socket. This will remove the bolt easily. Remove the washer from the bolt and thread the bolt back in several turns. This protects the threads at the end of the crankshaft, and also makes for a good pressing surface.

Installation is easy as well. The tool threads into the end of the crankshaft, and then you tighten a nut while holding the tool and that presses the damper back into place.

The only other consideration is the front seal. It's likely to be a rope seal. Rope seals are normally installed from the rear of the front timing cover. That is something that takes practice to install and size correctly to keep from having a big oil leak. If when you remove the damper, you see a lot of little pieces of fabric sticking to it, that is the rope seal falling apart, and it should be replaced.

Thanks for the info guys. John; That is a very "inventive" tip on how to loosen the bolt. Sounds like I should have a front seal handy just in case. Thanks for the help.

I hope you haven't flipped out john, but are you saying to remove the bolt by jamming it and engaging the starter ?
Very dangerious and a stupid idea. That car uses a flow through starter and the shaft will bend very easily. There is no rope seal on the front of that engine. There is one on the rear of the engine, though. That engine uses a two piece balancer. The balancer pulley itself and a sealing sleave that goes over the crank front. It will be cut by the rubber seal and will need to be replaced or welded up.
While you have it apart Bucky, replace the timing gear set
and chain. Also check the fuel pump excentric on the cam.
It will have a groove cut into it from the pump. Do not put the oil slinger on backwords. Hopefully your balancer
pulley will be one piece with the sealing sleeve attached.
Do not even attempt this without removing the rad first.
That was the first engine i had. Brings back memories.
Good luck.

I agree with the other poster - you need to remove the radiator else it will get damaged, and you'll find that the job is much easier with the radiator removed.

I changed the damper, timing chain, and timing sprockets on a '76 Plymouth slant 6 about 4 years ago. The damper was needed since it had slipped 15 degrees, but the client could have gotten a few more miles out of the chain and sprockets, but she showed up with the car and already had a new set of chain and sproekts in hand (my daughter) and wanted these replaced as well.

You can run a test before tear down to get an estimate of how worn the chain and sprockets are. Remove the distributor cap so that the rotor is visible. Put a wrench on the damper nut/bolt and rock the engine back an forth. Note how far the crank rotates back and forth before nudging the rotor. This is the free play. The service limit is about 7 deg of play. If there is more than this, the chain and sprockets should be replaced. If the free play is less than 3 degrees, consider leaving it alone.

There is an oil seal somewhere on the front end of the crank shaft. It's probably in the timing chain cover.

If you have a dial indicator, when the damper is partly removed (still engaging the key), check the crank for run out near the seal. Push the end of the crank up an down, the check for the side to side direction. Also rotate the crank shaft and note any run out. The nearer to zero, the better. If the crank wobbles more than a few thousandths of an inch, the seal will not hold. However, if the seal was not leaking before tear down, the crank was probably ok. If you remove the chain cover, the oil seal should be replaced.

When I pressed the damper back on, I had only a set of general purpose pullers and found that I needed about a 2 inch thickness of spacers to push the damper back in place. I made my spacers out of two, one inch thick hard boards (left over counter top material). I bored a hole to fit the end of the crank and cut an internal slot to clear the key. These worked very well.

Let us know how your job turned out.

"I hope you haven't flipped out john, but are you saying to remove the bolt by jamming it and engaging the starter ?"

There is a time when experience is king. I am in fact serious, and with rare exceptions technicians have used this exact routine for decades. One of the exceptions is Honda. Their crankshaft rotates counter clockwise, so the trick does not work, it tries to tighten the bolt instead of loosening it.

As far as it being dangerous, you haven't thought it through. The worst thing that can happen is the socket slip from the damper bolt, and it simply falls off. With the breaker bar in a pipe and already against the floor, there is no where for it to "swing", so either the starter simply stalls against the torque or the bolt is removed. While the tightening torque spec is somewhere from 100-150 ft/lbs it's common to require 300-400ft/lbs to break the bolt loose. That means it's extremely difficult to remove that bolt most of the time.

BTW, this is not the only time where a mechanical means of tightening, or loosening a fastener is employ'ed. Watch a heavy equipment guy remove a wheel in the field where the nut torque is 1000ft/lbs some time. It may look dangerous, but with experience it's safer than straining yourself.

As far as rope seals in the front, again this is where experience comes into play. Lip seals in an engine were not common until the 60's. Buicks actually had a hard time changing their design until the late 70's on some engines. So, while a lip seal is possible, my expectation is this is a rope seal, and you have to remove the timing cover to replace it because it goes in from the rear of the cover.

I've removed every crank bolt with my impact gun. They are not that tight. nut torque on most heavy equipment is 200
lbs. times that by the number of bolts, maybe 8 ?
that is 1600 lbs holding that rim on. They are removed, well i remove them, with a 6 foot Johnson bar. You are
assuming the guy that removes his crank bolt with a starter
has brains. Most of the time he will forget to disable the
ignition and the motor will start. Seen it. One hell of a mess. the crank bolt spun out and jammed on the last few threads as the bolt fell out. The socket and bar were still
attached. the pipe fell out. the bar spun slicing the rad
in half and smashing the water pump off the block and lodging into the fender. In my opinion a very stupid idea.
Oh yah, the crank had to be replaced. Believe me that Y
block DOESN'T have a rope seal on the front. Never had.
Even the 232 and 260 V8's have lip seals. I know, i've rebuilt them all. My flathead ford motor has a full circle lip seal on the front. Original equipment. Regardless, the timing cover has to come off to replace the seal. This is not a Buick motor.

Then they should probably stop selling them.

http://www.reds-headers.net/index.php?main_page=product_info&products_id=620

As far as things going wrong, it happens. Let me see you get your impact and loosen the crank bolt on a Subaru Legacy 2.5l.

I don't do them, John. I know when to quit. Even the all american 3 are getting out of control. To be very honest
John, ive spend most of my early years working for an engine rebuilder,I've rebuilt many flathead ford motors
and 313, 426 hemi motors. I dought you've seen a 217
small hemi. I have. I'm that old. I could be wrong being from Canada but i've NEVER EVER seen a rope front seal. EVER. The Canadian and American engines are different. Even
different colours. See, we even spell " colour " differently. ( you spell it "color". We used the rear axle
housing halfs off the model T fords for jack stands in the dealership i started in. ( a ford dealer ). From mechanic
to mechanic believe me that man's Y block does not have a
front rope seal. I think i still have a few of those seals
in my tool box that kind of accidently got there among others. It's a standard size that can be used for axle seals too. We should convers privatly. I'll teach you and you can teach me. Never to old or to young to learn. When
was the last time you worked on a 1947 Red Seal Continental
flathead motor. ( 47.3 H.P. @ 2000 R.P.M. )? 4 cyl. air
cooled inline Onan ? How about a 2 cyl. Witte diesle ? Yes
i get all the crap no one wants to work on or knows how to work on. I'm sure you get the same. Hope your weekend is good. I'm sure we will talk again.

Unless I somehow manage to buy something that has one of those engines in it, I'll never see nor work on any of them. That simply isn't what I do as a full time tech that works on todays cars. I can tell you though, what is expected of me would be to be able to service any one of them correctly the first and only time I would ever see one. Notice I did not say "I could do it", I said I would be expected to be be able to do it, realisticly or not.

I could counter your "when was the last time" with stuff like reprogramming, and calibrating the OCS/ORC systems in a 2005 Town and Country, and an entire myriad of other steps like that, that I often seem to do one time, and never repeat.

I try not to think of myself as old, but I do remember seeing others who were then my age back in my youth and I thought THEY were old.

Back to the rope seal, I was used to doing lip seals in the timing covers long before I encountered my first rope seal. I can also say, I've done enough of them to be able to do them with minimal seepage, they by design will never be "leak free".

Watch the news tonight. You will see a tiny piece of where I live. I don't know how but Obama picked this tiny town as his first stop after the convention. That's going to make driving around here this afternoon a nightmare....