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Tim's Auto Repair
Tim's Auto Repair, mechanic
Category: Chevy
Satisfied Customers: 15367
Experience:  Have owned a repair shop for 25 yrs.
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I have a 2002 trailblazer 4.2L engine knocks when warm doesnt

Resolved Question:

I have a 2002 trailblazer 4.2L engine knocks when warm doesnt when cold good oil pressure,compression,ext what could it be?
Submitted: 6 years ago.
Category: Chevy
Expert:  Tim's Auto Repair replied 6 years ago.


how many miles is on it?has it been hot or anything in the past?tell me all you can


Customer: replied 6 years ago.
it has 148,000 on it no it donesnt get hot hasnt been hot it wasnt doing it at all then it started like a pecking noise when it ran for awhile now it seems to b worse just at an idle it taps then about 3000rpm its fast then the car shifts and it slows down with the motor. if u pull out of somewhere and stop it it wont do it at all. i took it to a shop and the guy said it wasnt a piston he thought it was a lifter cuz it had good compression,
Expert:  Tim's Auto Repair replied 6 years ago.


this sounds like the connecting rod bearings are need to replace these as soon as possible or you may need to replace the crank shaft...the reason it don't knock when it is cold is because the oil is thicker and will hold better will need to remove the oil pan to do this..this is a 18hr job


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Service and Repair

Oil Pan Replacement

Removal Procedure


  1. Remove the A/C compressor bottom bolts (4) and loosen the top bolts (2, 3).
  2. Remove the oil level indicator and tube.
  3. Raise the vehicle.
  4. Remove left and right front tire and wheel assemblies.



  1. Remove the engine protection shield mounting bolts.
  2. Remove the engine protection shield.



  1. Remove the steering gear crossmember, front.
  2. Remove the left and right wheel drive shaft.
  3. Remove the front drive axle clutch fork assembly.
  4. Disconnect the prop shaft from the front axle pinion yoke.
  5. Remove the oil pan drain plug and drain the oil.



  1. Unclip the transmission cooler lines from the engine block.
  2. Remove the front differential bolts and set aside the front differential.
  3. Remove 4 transmission bell housing bolts that are attached to the oil pan.
  4. Remove the remaining oil pan bolts.
  5. Place 2 oil pan bolts in the jack screws on the oil pan and tighten evenly to release the oil pan from the engine.
  6. Clean and inspect the oil pan.

Installation Procedure

Important:The oil pan must be installed within 10 minutes from when sealer was applied



  1. Apply a 3 mm (0.12 inch) bead of sealer GM PN 12378521 to the block, rather than the oil pan.
Important:When you install the oil pan, it could be shifted front or back a little which could cause a transmission alignment problem. The back of the oil pan needs to be flush with the block.
  1. Install the oil pan, maneuvering the oil pan to clear the oil pump and screen assembly.
  2. Install the oil pan bolts.



  1. Inspect the oil pan alignment. Use a straight edge on the back of the block and the oil pan transmission mounting surface.
  1. Install the oil pan bolts.
    • Tighten the oil pan side bolts to 25 Nm (18 ft. lbs.) .
    • Tighten the oil pan end bolts to 10 Nm (89 inch lbs.) .
  1. Install the 4 transmission bell housing bolts that attach to the oil pan. Tighten bolts to 47 Nm (35 ft. lbs.) .



  1. Install the A/C compressor 2 bottom bolts (4). Tighten all 4 bolts to 50 Nm (37 ft. lbs.) .
  2. Install the front differential bolts. Tighten the front differential bolts to 85 Nm (63 ft. lbs.) .
  3. Install the front drive axle, clutch fork assembly.



  1. Clip transmission cooler lines to block.
  2. Connect prop shaft to front differential.



  1. Install the steering gear crossmember.
  2. Install the left and right wheel drive shaft.



  1. Install the oil pan drain plug. Torque the oil pan drain plug to 26 Nm (19 ft. lbs.) .
15.Install the engine protection shield and secure with the bolts. Tighten the engine protection shield bolts to 25 Nm (18 ft. lbs.) .
  1. Install the left and the right front tires.
  2. Lower the vehicle.
Important:Inspect the engine for oil leaks in order to ensure all sealing surfaces are sealed.
  1. Service the engine with oil.
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