Here you can find information regarding the assembly of the Chevy 3.5L OHV 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 3.5L 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 37 ft-lbs and then for the third time you do an additional 77 degree turn for each bolt. Be
sure to do each side of the caps before moving to another cap.
Once finished you should be good to continue with the rest of the engine.
Chevy Impala 3.5L Main Cap Torque Specs : 37 ft-lbs + 77°
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. Both surfaces should be cleaned and preped prior to installing. After preparing the contact surfaces carefully
install the oil pump onto the bottom of the engine block right onto the rear most main cap. There should be two pins which hold the pump in place
so that it does not shift during installation. When placing the pump onto the engine be sure that you have the pumps drive shaft held in place and
that both sides are well connected. It should easily slide into the holes without much force. If everything is good you should be able to place the pump
and shaft into place and then hand tighten the single pump bolt. Once hand tighten be sure that the pump functions when the shaft turns. The single oil pump
bolt can be tightened down to 30 ft-lbs. The oil pump pickup tube gets installed onto the pump directly and simply presses into place. Be sure to have the
pickup at the proper angle for you oil pan. Having this wrong will cause the pan to hit the pickup or the pickup to not access enough oil. The angle should be
about 15 degrees from the engine block flat surface. I personally will spot weld the pickup tube onto the pump so that it does not shift. However this step is not
neccessary. The oil pump drive gear clamp bolt can be torqued down to 27 ft-lbs if removed.
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. On Chevy OHV engines there is occasionally
bolt holes on the engine block that cross into water passages. Any hole that does this should be installed with some silicon sealant.
A little goes a long way in this step and you can check holes by shining a flashlight down them and looking in the water jackets.
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 3.5L OHV engine uses a single set of head bolts per cylinder head
make sure to use new head bolts as old bolts can be stretched and will not torque down properly. The cylinder head bolts tighten down to
44 ft-lbs and then a 95 degree turn for each bolt. Be sure to go through each bolt during each step before moving onto the next value.
On the Chevy 3.5 OHV engine the timing system is ran by the use of a chain. This chain system consists of a sprocket on the single center located camshaft
and one sprocket on the engines crankshaft. Since the camshaft is located in the center of the engine it needs to be installed from the front side of the
engine. The camshaft bearings get installed using a special cam bearing installation tool. The tool simply presses the bearings in and out of the bearing holes
using different sized plates to press on them. Be sure that all of your camshaft bearings are in good condition prior to installing the camshaft and building the
engine as this is a critical part of the engine. If all bearings are good and in place the camshaft can be lubed and placed into the engine. It should slide
into the bearings with ease, if it gets caught do not force it as you risk damaging the bearings. Simply move the camshaft end around until it slides in. Once
all the way into the engine you will need to install the camshaft retaining plate and its bolts. Depending on your specific chevy engine the camshaft retaining
plate gets installed impediately after the camshaft is slide into place or after the timing gear has been installed. Depening on how you took apart your engine
and the new parts you are installing you will need to adapt accordingly. The retaining thrust plate bolts need to be tightened down to 8 ft-lbs. The timing
sprockets simply slide onto both the crankshaft and the camshaft end. Be sure that you install the system all together with the timing chain marks lined up
with the dots on both sprockets. On the camshaft side it aligns using a dowel pin that sticks out of the camshaft and on the crank side there
is a woodruff key that aligns the sprocket onto the crank. With the sprockets in place you can begin to tighten down the camshaft sprocket actuator
bolts to 12 ft-lbs. Since the engine can turn while tightening be sure to hold the engine components and to use a proper torque wrench. On this
engine there is also a timing chain tensioner that is held onto the left side of the timing chain. This tensioner needs to be installed and torqued down to
15 ft-lbs. From here you can install the rocker arms and lifters with their retainers before installing the cylinder head.
The timing cover on the 3.5L is used to cover up the internals of the engine and hold in massive amounts of oil. For this reason I recommend using
some silicon sealant along with a new gasket during installation. Be sure to clean all of the metal surfaces prior to installation and placing the silicon onto the metal.
With everything ready to install be sure to double check your timing and engine internals before placing the cover in place. Another tip is to lube up the
crankshaft seal with some oil so it seats better. If everything is good to go then place the cover
onto the engine block and begin to tighten down the bolts hand tight. Once all of the bolts have been hand tightened be sure to follow your sealant
manufacturers specifications and then tighten the bolts down to 18 ft-lbs. Most silicon sealants require you to wait a specific amount of time before torqueing
so be sure to follow that to ensure no oil ends up leaking out.
Much like the timing cover on the 3.5L 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 bolts torque to 18 ft-lbs in a cross pattern design.
Along with the pan is the oil pan drain plug, this gets removed and reinstalled quite frequently and can be
torqued down to 18 ft-lbs.
Chevy Impala 3.5L Oil Pan 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 get tightened down differently depending
on whether they are the upper bolts/studs or the lower bolts. The lower intake bolts can be torqued down to 10 ft-lbs while the upper bolts should
be torqued down to 18 ft-lbs. The ignition coil module can be tighten down to 18 ft-lbs and the spark plugs themselves can be
torqued down to 11 ft-lbs, be careful not to overtorque these as they can snap and cause big problems.
When installing the throttle body make sure that all of the gaskets are in good condition and will hold a seal as you do not
want to be leaking gas fumes around the engine. If everything looks good you can tighten the throttle body bolts down to 8 ft-lbs.
Chevy Impala 3.5L Throttle Body Torque Specs : 8 ft-lbs
Exhaust Manifold Installation
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 it 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 18 ft-lbs.
The EGR system consists of a series of pipes that range from the manifold to the head. The EGR pipes on this engine can be
tightened down to 21 ft-lbs.
The water pump on the Chevy 3.5L engine should be installed by using
a new gasket and if desired some silicone sealant to help prevent leaks. Be sure to clean both metal surfaces prior to installing the pump. Once
prepared the pump can be moved into placed and then tightened down. On this engine the water pump tightens down to the engine block using 8 ft-lbs
of torque. Be sure to tighten down the bolts in a cross pattern to ensure no leaks develop. The water pump pulley can then be tightened down onto the pump
itself using 18 ft-lbs of torque.
Chevy Impala 3.5L Water Pump 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 52 ft-lbs and then an additional 70 degree turn. This is extremely tight so I recommend holding the
crankshaft somehow during the tightening procedure. The drive belt
tensioner bracket can be tightened to 40 ft-lbs and the idler pulley bracket can be torqued down to 22 ft-lbs. The idler pulley bolt can be tightened
down to 37 ft-lbs. When installing be sure they
both turn smoothly and if they do not then replace them with new ones as the bearings 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 should be tightened down to 25 ft-lbs. The alternator can be tightened down to
37 ft-lbs.
