4.2 Engine Rebuild

dglenn247

Member
Nov 14, 2018
2
Ohio
I apologize if I'm asking in the wrong place. Does anyone know what spec bolt is used for the cam position sensor on the 4.2? I have lost mine. I have not been able to find any documentation on it.
 
Jan 10, 2018
134
Michigan
This is all fantastic. after looking far and wide ive yet to find anything as helpful as this. After a long break from posting about my Turbo I6 ive finally started working out how to do everything. but with plans to possibly rebuild the engine first its been a long hard time trying to figure out what to do. Congrats on the rebuild and Thank you for all the awesome pics and detailed process'
 
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nevrvoyagain

Member
Mar 22, 2019
1
Delaware
Great information above....will definitely use it. I am rebuilding my mother-in-law's 2008 Envoy. The issue I have is the piston ring size for the LL8. Rockauto has two different sizes. One is 1.2 x 1.5 x 2.5mm and the other is 1.2 x 1.2 x 2.5mm. Which one is correct for this engine?

Thank you,
D
 

808

Member
May 5, 2022
209
Georgia
@m.mcmillen ... For the sake of your Readers, "The Legendary Mac" has proven that he is possessed of a level of Mechanical Knowledge and Experience that is Profound .... and this has given him the ability to tear this Atlas Engine down to its Atoms and then carefully re-construct it with confidence.

If any of you out there in "GMT Nationland" will follow in his footsteps... there are some things to do well before you "Put The Music" to it and Fire Up your Re-Built Engine. THIS is the time to Follow the Warnings of the Butterflies Inside your Stomach by Asking Yourself these Questions as your "Engine Break-In Engine Builder (15) Baker's Dozen:

(1) Did I Fill the Crankcase with Engine Break-In Oil and Additives?
(2) Did I Pre-Fill the Oil Filter before Screwing it on under the Engine Block?
(3) Did I Charge the Battery The Night Before The Big Day?
(4) Did I Fill the Radiator with Fresh 50/50 GM Approved Coolant?
(5) Did I secure a Reliable "Spotter" to be On Time on The Big Day?
(6) Do I Have a Basic Tool Set and Shop Rags on Hands to deal with any Leaks?
(7) Do I have enough Extra Coolant to Add to the Radiator & Keep it Topped Off?
(8) Do I have a Charged ABC Fire Extinguisher available & off to one side?
(9) Did I R&R Pull the IGN (Ignition Relay #22) to Oil Prime the Engine?
(10) Did I pour in some Chevron Techron into the Gas Tank to Prepare the Fuel?
(11) Did I Remove the Wheel Chocks & any Safety Equipment around the Vehicle?
(12) Have I Checked and advised Family, Friends, Neighbors NOT to stand nearby?
(14) Did I say that One Last, Fervent Prayer to the God of the Mechanical Universe? (Yeah... I skipped one # I'm superstitious about certain numbers)
(15) Do I have the Best Pizza Shop on my Speed Dial?

View attachment 79107

When at last "The Moment of Truth" arrives... have your Spotter available to watch closely Before, During and After the 30 Minute Period of The First Engine Start and Break In Period, The Spotter must be very responsible while acting as your Eyes and Ears scouring the Engine from Top to Bottom while you watch the Critical Engine Gauges for nominal Engine Oil Pressure and Coolant Temperature. After the engine comes up to the Proper Operating Temperature... Try to vary your RPM VERY GRADUALLY between idle and 1,500 RPM... and avoid doing any "Snap Throttle" actions to "surprise" this engine.

The last thing you want to do is force Brand New Rings on Brand New Pistons inside "unseasoned" Cylinders to be Over-Stressed before they have even had the chance to get introduced to one another. IF ANYTHING UNUSUAL HAPPENS... SHUT OFF THE ENGINE AND OBSERVE WHAT IS HAPPENING UNDER THE HOOD. Listen... Look and STOP the Motor if your Oil Pressure Gauge DROPS below 12 PSI or Goes to ZERO. This phenomena can happen if the Pre-Set Spring in the Constant 65 PSI Oil Pressure Valve inside the Oil Pump should jamb.... and also if you used Molybdenum Di-Sulphide or Very Thick Engine Assembly Lube in such a quantity as to CLOG THE OIL FILTER VERY QUICKLY. ....................DO NOT PANIC!....................

Just Install a Brand New Oil Filter after Pre-Filling it to the Brim with Engine Break-In Oil, go through the Same Start-Up Procedures as before. You should be "Out of the Woods" and the problems encountered by Hansel and Gretel after the 30 Minute Break-In period. Check all Fluid Levels... Then Do that Famous Victory Dance that will make your Neighbors think you have Lost Your Mind. It will be time to relax and Eat Some Pizza (leave the Beer-Wine for later). When you feel up to it... take the vehicle for a very leisurely drive for around 10 Minutes through the Neighborhood... listening for anything unusual and once back home in your driveway... shut down the engine and slip a Large and Long Piece of Cardboard underneath the areas of the Engine AND the Transmission. Check on this cardboard after 15-30 minutes for any unusual leaks.

Note any secondary Codes or Warnings collected on your Scanner that can be handled later on and after a requisite GM Dealership CASE Re-Learn for the Crankshaft and Transmission gear timing issues and a PCM Software Update ...you should be Good To Go! Drive this vehicle to the First 500 Miles NORMALLY WITH NO RADICAL STRESSES ON THE MOTOR!. Then CHANGE THE OIL AND OIL FILTER USING THE SAME ENGINE BREAK-IN OIL AND ADDITIVES. Once again only... Do this very same procedure at 1,500 Miles. Finally... at 3,000 Miles, switch to Mobil1 and K&N Oil Filters ...and after that every 3,000 Miles for "As Long as Grass is Green... and Skies are Blue...".

"Happy Motoring...!"
DUDE I'M SO STOKED I JUST FOUND THIS POST OF YOURS AGAIN. *ABSOLUTE GOLD*. THANK YOU.
Talk about *PROLIFIC*&*ENTRENCHED INVESTMENT* good Sir.
HAIL.
 
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mrrsm

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Member
Oct 22, 2015
7,639
Tampa Bay Area
Re: Post #s 63, 64 & 65... Dropping in a Video I did on un-boxing a Brand New Victor Rienz Rear Crankshaft Seal Unit for the GM - GMC 4.2L LL8 Motors purchased years ago from RockAuto:

 
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