It is time for an engine overhaul

Regulator

Original poster
Member
Nov 20, 2011
2,496
I am currently at 250k miles and everything is still running strong. I am burning about 3 quarts of oil over the life of the oil change, which is averaging 10k miles per the oil monitor system. I was really wanting to break 300k before replacing the motor, however due to a recently destroyed front differential I need to move my timeline up.

I have recently purchased a 2002 Trailblazer to use as a parts truck, I have understood that it had around 120k miles on it. The engine is out and on the stand and ready to get torn down. I have no experience once it comes to tearing down the engine and will be relying on some friends and a mechanic buddy to do the majority of the work while I play tool boy and watch and learn.

I am interested in the communities thoughts on what they would do and how far they would go into it. My mission is two fold, primarily it is a daily driver, secondary is off roading. I will be upgrading the rear end to the SS 14 bolt with 4.10 gears and replacing the front diff at the same time. I will also be adding a locker into the rear end. I will be moving up to a slightly larger tire, probably a 35" mud terrain. I am ultimately looking for more low end power and torque. This is not a race truck, but I would like to have the power at the wheels for low speed rock crawling without having to feel like I am having to continually running the throttle up.

So, with that all said, what would you do to clean / modify / improve the 4.2L engine and transmission?
 

Mooseman

Moderator
Dec 4, 2011
24,744
Ottawa, ON
Going way back to my old hot rodding days, you could do the usual porting and polishing of the head as well as port matching the intake and exhaust ports to help it breathe better overall. Maybe trying to find a custom camshafts to give you more low end torque would be good but finding performance parts for the I6 is no easy feat but did find one company that specializes in the Atlas I4, I5 and I6 engines. EMTechMotorSports might be able to help you out. If you do modify anything major, you're probably going to have to get a custom reflash of your PCM. PCM4Less may also help you out to find performance parts as well as the reflash.

Whatever you do, it would be interesting if you did a pictorial of the tear down and rebuild of our unique engine.
 

navigator

Member
Dec 3, 2011
504
It seems like there is some kind of performance intake you can get to add a little help but I am unsure outside of a tune what else you could do.
I think I would throw the used engine in as is and maybe step up to 4.56 gears instead of spending a lot on engine upgrades.
 

Dad-O-Matic

Member
Dec 5, 2011
228
If I recall correctly, limequat has said you can re-sleeve it with the Atlas 2.9/3.7 cylinder liners and pistons and bump up your displacement to 4.5 liters. I'm not sure if it's dependent on the year model of the engine, maybe you could IM him and find out. If I were doing a teardown, that's the first thing I would do. There's no substitute for cubic inches
 

jrSS

Member
Dec 4, 2011
3,950
Well regulator not knowing how well the engine runs would probably be a good idea to do a rebuild..unless he wants to take that chance with 125000 miles on it. I say rebuild it!!!!
 

limequat

Member
Dec 8, 2011
519
Dad-O-Matic said:
If I recall correctly, limequat has said you can re-sleeve it with the Atlas 2.9/3.7 cylinder liners and pistons and bump up your displacement to 4.5 liters. I'm not sure if it's dependent on the year model of the engine, maybe you could IM him and find out. If I were doing a teardown, that's the first thing I would do. There's no substitute for cubic inches

Yep, I had said that. However, Efi-diy doesn't think you could replace the sleeves with the I5 units. I'll defer to him since he's actually done a sleeve replacement and I have not. Maybe it would be possible with aftermarket sleeves?

I agree with the comment on steeper gears. Minus displacement and boost, the only way to get more torque down low is with gearing.

Then for incremental power increases: Tune, efan, intake, exhaust. I'm not convinced the last 3 are worth the money.

The chief engineer on the 4.2 says that you'll get 30 hp if you run dual exhaust. There's a guy near me that will split the stock manifold for a reasonable price. I wonder if that could be fed into an SS exhaust?
 

strat81

Member
Dec 29, 2011
399
I'd replace stuff like intake, exhaust, and head gaskets; spark plugs; valve cover gaskets, water pump, thermostat, etc. (I.e., do the maintenance stuff)

Inspect the valves, make sure they're in good shape, no sign of burning (replace as necessary). With the head off, run it through a solvent tank to clean out any accumulated sludge.

Do a compression test. If things look good, I'm not sure I'd bother to mess with the rings.

If you're after speed, you're better off selling the 4.2 and dropping a 5.3 or 6.0 in. I wouldn't try chasing after performance parts for the 4.2 - just get a tune done and call it good.

For the trans, there's 87 places that make and sell parts to improve the 4L60E. I'd be more concerned about the health of the transmission than the engine. Maybe rebuild it to 4L65E specs.


Don't forget to clean the throttle body. :biggrin:
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
NOS dude NOS!
 

Irishboy02

Member
Apr 1, 2012
222
Do you have any idea what is causing your oil loss? Is it a visible leak or is it burning away. I would say bore it out and re-sleeve. Obviously all gaskets and inspect your crank and camshaft for uneven wear. Might look into a custom camshaft to set you up with some power where you want it. Gears will help, but can hurt you on the highway as a daily depending on what you wind up doing.

Maybe try to find a 5.3 and swap that in - might be more cost effective. Not to mention the power increase, and my Sierra now on 35s with 3.73s gets better mileage than the TB did on 33s with 3.42s, in a bigger heavier truck.
 

Pittdawg

Member
Dec 5, 2011
538
Irishboy02 said:
Maybe try to find a 5.3 and swap that in - might be more cost effective. Not to mention the power increase, and my Sierra now on 35s with 3.73s gets better mileage than the TB did on 33s with 3.42s, in a bigger heavier truck.

A 4.2 liter TB with 33's and 3.42's cannot get out of its own way. I'm not all surprised you had bad mileage with that combination.
 

Irishboy02

Member
Apr 1, 2012
222
Pittdawg said:
A 4.2 liter TB with 33's and 3.42's cannot get out of its own way. I'm not all surprised you had bad mileage with that combination.

Actually wasnt that bad overall. Was much better on the highway then around town, guess it was able to use its momentum.
 

pejeeper

Member
Jan 27, 2012
81
The real question is how much is your budget for this project, then prioritize accordingly to what you want.

Once you begin the tear down, your priorities may change depending on what you find inside.
 

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