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The rattle-type noise that affects these GM vehicles with 4.3L V6 engines may be caused by torsional vibration of thebalance shaft.

To fix the problem, follow the service procedure below forinstalling a new tensioner assembly kit. If detonation noise ispresent, perform detonation/spark knock diagnostic testing first.

Applicable Models: 1996-2003 4.3L V6Engines found in Chevrolet Astro, Blazer,Express, S-10, Silverado and P Models; 1996-2003 GMC Jimmy, Safari,Savana, Sierra, Sonoma; and 1996-2001 Oldsmobile Bravada applications.

PARTS INFORMATION

Part Number   Description
12458911         Chain Kit
89017257        Tensioner
10220906        Oil Pan Gasket
88893989        O-Ring and Gasket Kit
3754587          Water Pump Gasket (2)
89017259        Cover

Service Procedure:

1. Remove the engine front cover.

2. Remove the crankshaft sensor reluctor ring and line up the timing marks on the crank gear and camshaft gear.

3. Remove the camshaft gear and chain. For model years 1996-’98,remove the crankshaft sprocket using the J 5825-A crankshaft sprocketremoval tool.

4. Pull the shipping pin and discard. Remove the nylon timing chain tensioner blade from the timing chain tensioner bracket.

5. Position the bracket on the front of the engine. The upper twoattaching holes of the bracket will line up with the center two enginefront cover bolt holes. The lower bracket holes will line up with theengine front cover alignment holes (see Figure 1).

6. Use a hammer and the J 46165 pin driver to install the dowel pinsthrough the two lower holes in the bracket and into the engine block.Make sure that the bracket is held firmly in place before proceeding(see Figure 2).

7. For model years 1996-’98, install a roller-type timing chain set.Install the crankshaft sprocket using the J 5590 crankshaft gearinstaller. Install the timing chain around the crankshaft sprocket andposition the timing chain to the driver’s side of the engine.

8. Install the nylon timing chain tensioner guide onto the timing chain tensioner bracket pin and
position the top of the guide under the tab at the top of the bracket (see Figure 3).

9. Install the camshaft sprocket into the chain and then to thecamshaft. Install the bolts finger-tight. Make sure the timing marksare aligned, then tighten the camshaft sprocket bolt. Tighten the boltto 18 ft.lbs. (25 Nm).

10. Install the crankshaft reluctor ring.

11. Install the engine front cover and place a washer under the twocenter cover bolts that extend through the tensioner bracket. Thesewashers are required to maintain the proper crush on the engine frontcover seal (see Figure 4). Tighten the bolts to 106 in.lbs. (12 Nm).

By Tom Purser, ALLDATA editor, and Jeff Webster, ALLDATA technical writerfigure 1figure 2figure 3Figure 4

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