2008 Chevy Trailblazer 4.2L Complete Torque Specs List
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Chevy Trailblazer 4.2L Repair Information
Chevy Trailblazer 4.2L Engine Repair Information
Here you can find information regarding the assembly of the Chevy 4.2L engine. In this guide we will
start from the inside of the engine including the
crankshaft, connecting rods, and piston ring installation and then move outwards all the way to the pulley belt
system. Along the way correct procedures and torque specs
will be given to aid in the assembly of the engine. Feel free to start from the beggining and work your way
outwards or skip ahead to your current position in the engine for what you may need.
Crankshaft Main Caps Installation
The 4.2L engine block main bearing caps should be inspected for any defects or flaws before installation.
Be sure to lubricate the bearing surfaces prior to installation. Once prepared you can place the caps onto the crankshaft
and begin tightening the bolts down in a multi stage process. The first being 10 ft-lbs starting from the middle and going outwards.
The second time around you can go to 18 ft-lbs and then for the third time you do 2 additional 90 degree turns for each bolt for a total of 180
degrees. Once finished you should be good to continue with the rest of the engine.
Chevy Trailblazer 4.2L Main Cap Torque Specs : 18 ft-lbs + 90° + 90°
Piston and Connecting Rod Installation
To install the pistons and connecting rods you must first install the piston rings into each piston. Be careful
not to stretch the rings or break them during installation. Make sure to put the correct rings in the correct
positions, this can be determined by looking at
the instructions given with the new rings. Each ring manufacturer is different so be sure to check for your
specific rings. Once the rings have been installed you can now fit the connecting rod bearings into the end caps
and lube them up with oil or lithium grease. The piston can now be lowered into the cylinder, make sure the dot
or mark is facing the front of the engine and that you don't scratch the cylinder.
Once installed you can match the connecting rod caps with the correct rods and start to torque the connecting
rod bolts to 18 ft-lbs and then an additional 110 degree turn for each bolt. After all are done rotate the crank
to ensure all pistons move smoothly in and out of their cylinders and nothing binds.
When installing the oil pump be sure to use the proper sealant around the pump base if neccessary to ensure that oil pressure
doesn't drop due to leakage. After preparing the contact surfaces carefully
install the oil pump onto the crankshaft by aligning the crankshaft end with the hole on the center of the pump gear. Once
installed you can then place the bolts into the holes and tighten them down to 8 ft-lbs. The oil pickup tube on this engine then bolts up
to the bottom of the oil pump through the use of a single bolt. This bolt can be tightened down to 8 ft-lbs along with the tubes
retaining bolt. The oil pump pressure relief valve can be torque down to 10 ft-lbs if it has been removed for any purposes.
The first thing you must do when installing cylinder heads is to ensure both the block and head surfaces are
completely clean from dust, oil, and any debris. The next thing you must to is
to set the camshafts to their correct positions to prevent any valves from hitting pistons during installation
and torquing of the head bolts. Much the same you have to set the pistons to their correct
locations, typically this means putting the #1 piston to TDC or Top Dead Center. Once everything is ready you
can install the head gasket onto the engine block by aligning the alignment dowels.
Something I usually do is spray down the head gasket with some engine copper spray from permatex which you can
find here, this ensures that any gaps that could be present between the 2 surfaces gets filled with the
spray. It
also helps to transfer heat between the 2 metals. With the gasket in place you can set the cylinder head onto
the gasket and block, if needed have someone assist with this process as the head can be heavy
and you don't want to scratch anything or drop it! Once the head has been placed you will want to start
installing the head bolts to make sure it doesn't move. Be sure to buy new head bolts as many manufacturers
use TTY or Torque to Yield head bolts meaning they stretch during torqueing and cannot be used twice. Also make
sure to lubricate the bolts in clean engine oil before installing them into the head.
Once all the head bolts have been installed and finger tightened you can start the torqueing process, almost all
head bolts have a multi-step process for torqueing. The 4.2L uses 3 different sizes of cylinder head bolts in its
engine. In total there are 10 medium sized bolts, 2 short bolts, and one long skinny bolt. The medium sized bolts start off
with 22 ft-lbs and then get turned an additional 155 degree turn going through each bolt one at a time. For the short
bolts you can tighten them down to 5 ft-lbs and then a 60 degree turn. The long bolt can be torqued down to 5 ft-lbs as well
but then a 120 degree turn. After torquing the heads are completely installed and you can now move to intalling the timing.
On the Chevy 4.2 engine the timing system is ran by the use of a timing chain. This chain system consists of a
sprocket on each camshaft, a tensioner, timing guides, and a crankshaft gear. Before the chain can be put into place
you need to make sure that all of the gears are in their proper positions. Make sure that the intake and exhaust camshaft sprockets
and actuators are torqued down properly. The intake camshaft sprocket gets torqued down to 15 ft-lbs and then a 100 degree turn. The
exhaust camshaft actuator gets tightened down to 18 ft-lbs and then a 135 degree turn. The crankshaft sprocket simply slides into place and
aligns using a woodruff key that installs into the cranks shaft. Be sure that both camshafts bearing caps have been installed properly and
torqued down to 8 ft-lbs. From here we can install the timing chain and align the painted chain links with the dots on each sprocket.
Once aligned we can install the timing chain guides and torque them down to 13 ft-lbs. The top timing chain guide gets tightened down to 8 ft-lbs.
With all the guides in place you can install the timing chain tensioner and torque it and its shoe bolt down to 18 ft-lbs.
From here you can pull the tensioner holder and the chain should tighten up and stay in place. Double check the timing before turning over
the engine and ensuring that nothing binds up. If you also need to work on the rear timing chain which runs the balancer shafts off of the crankshaft
be sure to check out that section just below.
On the Chevy 4.2 engine there is a rear timing chain that runs the engines balancer shafts which mitigate the engines vibrations.
The balancer shafts run off of a timing chain that also connects to the rear end of the crankshaft. In order to change this timing chain you
will need to remove the transmission from the engine and then remove the rear timing chain cover. From here we can see both of the balancer shaft sprockets
along with the crankshaft sprocket which is fixed to the crank itself. To install a new balancer shaft simply remove the timing chain guide and then
remove the corresponding balancer shaft sprocket and shaft retaining plate. The shaft will then pull out and can be changed. In order to change the
rear timing chain you just need to remove the timing guides and then remove the old chain with a new one and then align the black painted chain marks with
the dots on the sprockets. Once aligned simply reinstall the timing guides and torque them down to 8 ft-lbs. The tensioner bolt can also be installed and
torqued down to 8 ft-lbs. The balancer shaft retaining bolts can be torqued down to 8 ft-lbs as well. The cover that keeps the oil in the engine and protects the
rear timing chain can be installed with a new gasket and some silicon sealant and then torqued down to 8 ft-lbs.
The front timing cover on the 4.2L is used to cover up the main timing chain and retain engine oil inside of the engine. For this reason I recommend using
a new timing cover gasket and some silicon sealant to ensure that the cover does not end up leaking. Once both contact surfaces have been cleaned
and the new gasket and silicon is in place and ready you can place the cover onto the engine and tighten down the cover bolts to about 8 ft-lbs.
Be sure to follow your silicon sealants manufacturers instructions as some require you to hand tighten the bolts and then wait an extended period of
time before torqueing them down.
Much like the timing cover on the 4.2L the oil pan plays an important role in keeping the engine oil inside the
engine. For this reason I recommend using a new gasket as well as some silicone sealant
during installation. Using the same technique as before with the cover you clean the surfaces of both the oil
pan and the engine block and then install the new gasket onto the block and then follow
it up with some silicone sealant. Be sure to follow your sealants instructions to ensure you get the best seal
from your application. The oil pan uses 2 different sets of bolts being the side bolts and the bolts that go up from the bottom
of the pan. The side bolts can be torqued down to 18 ft-lbs and the normal bolts can be torqued down to 8 ft-lbs.
Along with the pan is also the oil drain plug which is commonly removed and reinstalled. This can be torqued down to 18 ft-lbs.
Chevy Trailblazer Oil Pan Bolts Torque Specs : 8 ft-lbs
Chevy Trailblazer Oil Pan Side Bolts Torque Specs : 18 ft-lbs
The valve cover installation is rather simple, there are rubber seals for each bolt hole and a silicone gasket
that prevents oil from leaking out of the engine. It is recommended to replace both the seals
and the gaskets although if they are in good condition you can reuse them. If you do choose to reuse them I
would use some silicone sealant along with the silicon gasket to ensure it does not leak.
The valve cover bolts torque down to 106 in-lbs or about 8 ft-lbs in a criss cross order. Be sure not to miss
any bolts to avoid having oil leak out onto the exhaust pipes and cause a lot of smoking.
When installing the intake manifold you want to make sure you have all the surfaces as well as intake holes
cleaned out before placing the manifold into position. Once cleaned you can then place
the intake manifold gaskets onto the alignment pins. If you want you can also use a little bit of sealant on the
gaskets to help ensure there are no leaks. With the gaskets in place you can now put
the manifold down onto the gaskets and begin to install the bolts. The intake manifold bolts torque to 8 ft-lbs
and can be tightened starting from the inside and going outwards. The ignition control module can be torqued
down to 8 ft-lbs and the spark plugs themselves can be
torqued down to 13 ft-lbs, be careful not to overtorque these as they can snap and cause big problems.
When installing the fuel rail make sure that all the fuel injectors are in good condition and that all the
o-rings are in place and
are in good condition. If everything is good you can place the fuel rail into position and push the injectors
into their holes and start to torque the rail bolts to 90 in-lbs or about 8 ft-lbs.
The exhaust manifold can be installed by cleaning the surface areas on both the head an the manifold itself and
then by using the exhaust manifold gasket and putting it in place. Once the gasket is in its
location you can put the manifold onto the heads and begin to torque the fasteners down to 15 ft-lbs. I always use some
copper spray from permatex on the exhaust manifold gaskets to ensure I do not end up with
any exhaust leaks once done. When you go to install the engine into the vehicle or if it is already in the
vehicle the torque specs for the exhaust manifold to the exhaust pipes or catalytic converter is 35 ft-lbs.
The EGR system consists of a series of pipes that range from the manifold to the head. All of the EGR pipes can be tightened down
to 14 ft-lbs.
The water pump on the Chevy 4.2L engine should be installed by using
a new gasket and if desired some silicon sealant to help prevent leaks. Be sure to clean both metal surfaces prior to installing the pump. Also
lookup your silicon sealants instructions to ensure that you are doing everything properly. The water pump bolts can be torqued down to 8 ft-lbs,
the coolant outlet bolt can be torqued down to 8 ft-lbs and finally the water pump pulley bolts can be torqued down to 18 ft-lbs.
Chevy Trailblazer Water Pump Bolts Torque Specs : 8 ft-lbs
Chevy Trailblazer Water Outlet Bolt Torque Specs : 8 ft-lbs
Most of what is left on the engine is just place and tighten objects such as the belt pulleys, belt tensioner,
throttle body, oil filter neck, crankshaft pulley, and motor mounts. If the items have a gasket and hold either
oil or coolant inside the engine then feel free to add some sealant along with the gasket. Always be sure to
inspect your gaskets and replace them if there is any deteriation or flaws with them. For the
belt system the crankshaft pulley gets torqued to 110 ft-lbs plus an additional 180 degree turn. The belt
tensioner assembly can be tightened to 37 ft-lbs. The idler pulley bolt can also be torqued down to 37 ft-lbs. When installing be sure
it turns smoothly and if it does not then replace it with a new one as the bearing can go bad. The engine
motor mount can be installed onto the engine block if it hasn't been already, the torques for
the mount to the block is 59 ft-lbs and then when installing the mount to the vehicle or frame it can be torqued to
35 ft-lbs. Finally the throttle body can be installed on top of the intake manifold
with a good gasket and some added sealant using 7 ft-lbs in a criss cross pattern. For installing the belt you
can use a tool to move the tensioner into its springed state and install the belt as shown in the
picture. The power steering pump bolts should be tightened down to 18 ft-lbs. The A/C compressor can be tightened
down to 18 ft-lbs. The alternator mounting bolts get tightened down to 37 ft-lbs.
