1970s 1970 timing chain

[Jim Miller]

As the timing chain on a 472 loses plastic bits (I assume age gets them all at some point), does it and how does it affect the idle?
My 1970 CDV has 8,200 miles and everything is tuned to spec. Sometimes she idles very smoothly like a Cadillac should. Sometimes it's not quite as smooth. If I set the idle higher than spec she is smoother but will diesel if shut off warm. On the road she runs very smooth and great acceleration.
The carb has been overhauled, she has new points, plugs, wires, condenser, rotor, and cap. Not certain what else to check other than accept that sometimes she the idle may be off a bit.
Thoughts and suggestions appreciated.
Thanks 

["Cadillac Kid" Greg Surfas 15364]

As has been and I'm sure will be repleaded ad nauseam, the Nylon coating on the cam gear longevity is a crap shoot. It seems some go for hundreds of thousands of miles and some just fail with age. Since your '70 is an interference motor ( the valves will hit the pistons if out of sync) If this were mine I would definitely do a timing set replacement.  In regards to the intermittent idle issue, If the culprit were to be the timing set, it would most likely be a constant issue.
Greg Surfas

[TJ Hopland]

How steady is the timing when you look at it with a timing light?  If its kinda floating around that may be an indicator its loose.  How about dwell with a meter?  Is that reading steady?  I know you said low miles but maybe lack of use got to the bushings in the distributor so the shaft has some wobble to it now which will make the timing a little mushy and show up on a dwell meter.

A quick(ish) check to see if or how loose it is is to rock the crank back and fourth with the distributor cap off and watch the rotor to see how much rotation it takes to catch up when you change the crank direction.   

The ish part comes in that Cadillac didn't use a crank bolt in these engines (unless 70 was different due to the 1 year only balancer setup?).  You cab buy one but its not something a typical hardware store will have so you would have to get it from a Cadillac engine vendor or larger hardware source such as McMaster Carr.   Spark plugs out maybe you could do it by grabbing the fan or alternator fan?

If you pull out the distributor you can usually get enough of a look down there to see that it is or isn't plastic and if its pretty bad you should be able to tell.  Bore scope which are cheap now is an even better way to see down there and could also be done through the fuel pump hole if you don't want to mess with the distributor. 

[Jeff Rosansky CLC #28373]

didn't use a crank bolt in these engines (unless 70 was different due to the 1 year only balancer setup?).  You cab buy one but its not something a typical hardware store will have so you would have to get it from a Cadillac engine vendor or larger hardware source such as

I believe a 9/16 fine thread bolt will fit.

[The Tassie Devil(le)]

Don't forget to pull out the cork.

Bruce.