I replaced my resistor plugs with platinums, but it took awhile to get the last one out and replaced. I drove it for a day with 7 new and 1 old plug. Idle was not as smooth but not too rough.

Now with all new plugs, I hear an ugly high pitched scraping noise at start up. I immediately shut the car down and have not touched her since. It's a W126 with 163K and what I suspect to be an original chain. My search of the site seems to indicate timing chain and/or tensioner. I'd appreciate any input.

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1991 560SEL (254K miles)
1980 Lincoln Mark VI - Givenchy
1979 Lincoln Mark V Collector's Series
1979 Lincoln Town Car Collector's Series
1979 Ford "Effie" Pickup (in gradual transformation to a show/street truck)
1969 Lincoln Mark III (waiting for "Overhaulin" to call)
1989 Lincoln Towncar
2001 Lexus GS300 (spousal unit's daily driver)