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Old 09-09-2001, 11:46 AM
Dennis Taylor
Posts: n/a
1987 420 SEL timing

What is the correct static ignition timing for the 4.2L engine?

Just changed out the timing chain, one on the rail was broken. Vehicle has 246,000 miles on it.

Also #8 inlet valve has a clearance issue, not sure if the spring has lost tension, exchanging a lifter and rocker arm showed not to be the problem.

Any thoughts?
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Old 09-09-2001, 02:18 PM
Registered User
Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
If the timing chain broke, you most likey have a bent valve...You will have to pull the head to replace the valve.

When you roll the engine to #1 TDC on compression stroke, there is a mark that lighns up on the distributor rotor to the distributor housing...You can't adjust it other than this. It is crank fired, computer controlled ignition timing. All you need to do is get the rotor in the right place to jump the spark over.
Donnie Drummonds
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Old 09-09-2001, 05:07 PM
Dennis Taylor
Posts: n/a

Thanks Benzmac,

Before I started work on the vehicle it was rough at idle (purchased this way) PO had raised idle to 1100 Rpm whereby it smooth out. The timing chain was stretched so I purchased the parts thru partsshop and fastlane including the two lower rails, had to remove timing cover to install.

The car had not thrown the chain, the inboard left bank rail had broken below the lower support pin.

I have not accomplished a better running condition from the chain replacement but it had to be done. Pulling on spark plug lead at a time does not highlight any particular cylinder is not firing. It does smell rich and has a heavy miss in the exhaust, almost a "popping" sound.

This car has not had the maintenance it deserved from my untrained eye, perhaps 7500 mile oil changes.

I did replace the fuel filter a "flow" the fuel lines to check cleanliness and it appears normal.

Throwing money at the problem would be a mistake, (although the smog pump is removed and sent out for rebuild as we speak).
Would removing the fuel distributor system and having it rebuilt (by who?)be advisable at this time? I did install a new fuel governor on the CIS body two months ago as it was leaking fuel.
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Old 09-10-2001, 08:39 AM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
The *shim* between the rocker arm & the valve come in various sizes between 3.5 & 6.0mm so that you can adjust pretension on the lifters. If only one cylinder has a problem this is a good starting place.
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Old 09-10-2001, 11:22 PM
Dennis Taylor
Posts: n/a
420 SEL Timing


I added a new shim a got the clearance correct but no improvement in operation. The idle surges from 200 - 300 Rpm to 1000 Rpm where it smoothes out and then repeats the pattern but not always cyclical.

Does the CD for the 126 cover the 4.2L engine? I have the paper manuals but not the engine manual. Would be nice to have a troubleshooting "tree" to work thru.

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