EXHAUST MANIFOLD REPLACEMENT
*Courtesy of acaprez from his website and the MR2 Forum
Shortly after buying the car, I started
hearing an odd sound from the engine compartment. From suggestions I concluded
it was the exhaust system and after getting an overall inspection done by a
mechanic (Toyota Lexus Care in San Diego) I was told the exhaust manifold was
cracked. I took what TLC told me and ordered parts from Jay Marks Toyota in Houston, Texas.
I considered getting a TRD exhaust
manifold, but the price was too steep, and after reading this (go down to
exhaust) on The AW11 Archive I'm glad I didn't. For now the standard manifold is
fine for me. I came back from school on Friday to find out I still hadn't gotten
my parts because UPS hadn't come during the time they said they would the day
before. Luckily I got the parts that day.
Overtime I discovered I didn't exactly
order what I needed. I had ordered the intake manifold gaskets as well, when I
meant to order the gaskets for where the manifold connects to the rest of the
exhaust. I also needed a few studs and the gasket for the oxygen sensor, but
luckily I got those from a local Toyota dealer. And I'm sure I'll use the intake
gaskets one day as I plan to keep this car for a while.
Here is what you need for this job. I used
the Haynes manual and highly recommend it. I have heard many that the Toyota
repair manual is a better source, so I would use that if I could. You also need
the exhaust manifold gasket, the o2 sensor gasket, and two 'O' ring gaskets for
the other part of the exhaust. You might also want to replace all the bolts and
studs. That includes the three studs that connect the manifold to the exhaust
(blue circle), as well as their nuts, two studs, three bolts that attach the
manifold to the engine block (red), and the two studs for the o2 sensor (green).
I got by without replacing the two studs and three bolts attaching to the engine
block. An exploded view of what I'm talking about as well as part numbers can be seen below:
and the two exhaust o-rings can be seen here:
Those pictures are off Bill Strong's site and his great parts catalogue
I'd recommend spraying all the bolts you
need to take out at least a few hours beforehand with a penetrating oil. The
three bolts connecting the manifold to the exhaust were the hardest to get off.
One went without too much trouble, but the other two stripped. My grandpa ended
up helping me from that point on, and we had to cut through the nuts. The rest
of the exhaust was easy to get off, as was the manifold shielding.
From there on the only big problem we had
was the left most bolt under the distributor. I didn't want to remove the
distributor itself, and could only get one screw out of the distributor shield,
but that was enough to move it out of the way. We used lots of extensions on
that bolt, and loosened it from under the car. The other bolts went easily.
The next major step was getting the studs
for the o2 sensor out. We got them with a special tool, but getting them back in
was another thing since the thread was really bad. Two dealers in the area
didn't have those studs in stock (this was a Sunday, so not much was open) but
luckily Autozone had studs of the size I needed. Putting it back together was
much easier, although that bolt under the distributor was still tricky.
And one more comment, unless you want your
car to look like it's on fire, clean the new manifold before putting it in. I
think the smell is gone now, though. Here are my posts on the topic on the MR2
Owners Club Message Board. One
and two.
EXHAUST MANIFOLD REPLACEMENT
Introduction
Cracked exhaust manifolds appear to be quite common on MR2’s. This year it
happened to mine! It is an MOT failure point, so I was forced to fix it. I chose
to do the work myself, and this page is based on my experiences to help others
with the same problem! Symptoms are quite obvious: a raspy blowing exhaust
noise, and strong exhaust fumes smells around the rear of the car. If your car
has these symptoms it may be that the connection or gasket between the manifold
and cylinder head has failed, or the connection or gaskets between the manifold
and the exhaust pipe has failed. So check these first as they are much cheaper
to repair! If you have got a crack in the manifold you will most likely find it
next to number 4 cylinder (the one farthest from the engine bay cooling fan).
The common thinking is that the cooling fan cools the right side of the engine
(and hence manifold) more than it does the left, and therefore there are
internal stresses in the manifold due to different levels of heat related
expansion, causing the crack. The manifold has heat shields on its inner and
outer faces, and you must remove the outer one before you can see the manifold!
To remove the heat shield, and also to remove the manifold itself, you will
need to work underneath the car. I have a set of large ramps that I reverse the
car up, but an inspection pit would work even better. Axle stands will probably
not raise the rear of the car high enough off the ground for you to work
comfortably underneath.
Parts
I chose to renew all the fasteners and gaskets when I did this job. This was
for a number of reasons:
1. Some of the fasteners (particularly the bolts holding the heat shields)
are liable to snap.
2. The fasteners may be weakened by the removal process and so could snap on
refitting.
3. If I need to do the job in future newer fasteners should be easier to
remove than older ones.
Toyota dealers are usually happy to accept returns of unused parts, so any
you do not use you can get a refund for. I did this with the two manifold to
head studs.
If you need to replace the manifold then this is a complete list of what you
require if you also choose to replace all the gaskets and fasteners:
1 gasket for manifold to cylinder head
2 gaskets for manifold to exhaust pipe
9 bolts for inner and outer manifold heat shields
2 studs for upper edge of manifold to head joint
2 nuts and washers for upper edge of manifold to head joint
3 bolts for lower edge of manifold to head joint
1 bolt for lower manifold to bracket into engine block
3 studs for exhaust pipe to manifold joint
3 nuts for exhaust pipe to manifold joint
Procedure
Removing the outer manifold heat shield involves removing six bolts using a
10mm socket. Working from above, remove the three bolts on the top of the heat
shield. You will have difficulty seeing them, but you can find them by touch
easily enough (obviously make sure the exhaust system is cold before trying
this!). You will need an extension bar for your ratchet handle - a 5" one
is ideal. Note that the Haynes manual recommends removing both the distributor
and the throttle cable bracket before doing this, but I found that it was not
necessary to do so. Then, working from underneath the car, remove the two bolts
either side of the manifold just above the joint with the exhaust pipe, and the
one in the centre of the manifold about half way up. Hold the heat shield while
removing the latter and lower it down gently out of the way, being careful not
to snag any piping or wiring as you do so. From underneath the car you will now
have a good view of the manifold to exhaust pipe join, so check for carbon
deposits which would indicate that the joint is blowing (if it is blowing, and
the manifold appears ok, then just follow the sections below that deal with
disconnecting the exhaust, fitting new manifold to exhaust gaskets, and
reconnecting the exhaust). Have a look at the manifold too, just in case the
lower part of it has cracked (unlikely, but check anyway). Now look into the
engine bay from above and inspect the manifold. You will probably find it has
cracked next to the number 4 cylinder as in figure 1, but if not check the rest
of it for cracks. Do this by touch for the area next to number 1 cylinder that
is obscured from view by the distributor. If the manifold does not appear to be
cracked, and the manifold to exhaust pipe connection appears to be sound, then
the manifold to cylinder head gasket is probably blowing. Except for number 1
cylinder end you cannot see the gasket, so inspection is impossible with
everything still attached to the car, but if you suspect it is at fault then
remove the manifold as detailed below, check the manifold carefully for cracks
while it's off the car, renew the gasket and refit the manifold.
You will probably find that you snap the heads off some of the heat shield
bolts as they are very weak - so be careful just in case the manifold is ok
otherwise you will have to drill the bolt stems out before refitting the heat
shield! Given the very high temperatures reached by the manifold, it is wise to
refit the heat shields!
The next step is to disconnect the exhaust pipe from the manifold. Three
studs and nuts hold the two together. You will need a deep 14mm socket to remove
the nuts, due to the studs protruding. A 1/2" drive impact socket works
fine. You will also need an extension bar (5" is fine) as two of the nuts
are on the sides of the exhaust pipe, partially hidden by the exhaust pipe heat
shields (there is no need to remove the latter). I used a breaker bar to slacken
the nuts - it is a little unwieldy to use under the car, but it can be done! I
then used a normal ratchet handle to finish off removing the nuts. As you remove
the last nut, be sure you are holding the exhaust pipe firmly, otherwise it will
drop down quite forcefully (it is heavy) and could damage itself and you in the
process. Remove the two circular gaskets. The Haynes manual advises to remove
the exhaust completely (accomplished by removing the two bolts holding the
exhaust to a bracket near the tailpipes and sliding the whole assembly to the
left to clear the hanging brackets). I didn't do this, choosing instead to tie
the manifold end of the exhaust pipe to the front engine mounting using some
stout pieces of string. There was still plenty of room to work.
With the exhaust pipe now out of the way, you are ready to remove the
manifold. This is held on with two studs, nuts and washers along the top edge of
the joint with the cylinder head, three bolts along the lower edge of the joint
with the cylinder head, and one bolt securing it to a bracket near to the
connection with the exhaust pipe. The bolt next to number 1 cylinder can be seen
circled on the left of figure 2, and the bolt and bracket can be seen circled at
the bottom of figure 2. Attempt to slacken all the nuts and bolts before
removing the manifold in case something snaps (if it did my plan was to then
tighten the remaining nuts and bolts, reconnect the exhaust pipe and take the
car to a reputable garage for them to remove the snapped item and finish the job
off!). As it happens the nuts and bolts were easy to slacken, as the Toyota
specified tightening torque is just 25Nm. Just to be sure I sprayed each nut and
bolt with Plusgas release agent beforehand. You cannot see the two studs and
nuts along the top edge of the manifold due to their location, but you can find
them by touch quite easily from above. You will need a deep 14mm socket again,
and an extension bar (3" is fine). A wobble bar is useful for the nut
between number 1 and 2 cylinders, as the distributor is very close (a wobble bar
is an extension with a bevelled male end that allows the bar to move slightly in
the socket, allowing you to clear an obstruction - they are inexpensive and can
be very useful!). I used a breaker bar to break the nuts loose. Although these
are a little unwieldy they do allow you to apply a lot of torque, but in a very
controlled manner - exactly what is required to loosen nuts and bolts without
snapping them, so I recommend you buy one if you have not already got one.
Then working from underneath the car, break each of the three bolts on the
lower edge of the manifold to cylinder head joint loose, and the bolt securing
the lower part of the manifold to its bracket. Again I used a breaker bar, is
worth it for the reasons given above. I removed the plastic under-car protector
plate to give me better access (this needs a 10mm socket with a short extension
- be careful, the bolts are very easy to snap!). The bolt at the number 1
cylinder end is easy to get at up above the oil filter. The nut at the number 4
cylinder end is more tricky, and you will need to use a 3" extension,
optionally with a wobble bar. Even then it is tricky due to the variety of
pipes, control cables, engine mounts etc. in that area. You can get to the bolt
in the lower edge of the manifold between number 2 and 3 cylinders from either
below or above. Either way you will need to do so by touch as you cannot see it
due to its location! It is not difficult though, I chose to slacken it from
below. Finally, do not forget to slacken the bolt holding the lower part of the
manifold to its bracket.
Now that the two nuts and four bolts are loose, you are ready to remove them
and the manifold itself. Remove the two nuts (and their associated washers) from
the top of the manifold first (the studs will probably stay in place and help
you by suspending the manifold when you remove the bolts). Now, from under the
car, remove the three bolts holding the manifold to the cylinder head. Rock the
manifold to see if it detaches from the cylinder head. If it does not, tap it
with a rubber or plastic hammer until it does. It will only come loose at the
number 4 cylinder end because of the bolt and bracket on the lower part of the
manifold. Once it is loose, from under the car, hold the manifold securely with
one hand and undo the bolt holding the lower part to the bracket. Then using
both hands, pull the manifold off the studs and lower it down gently to avoid
damaging anything in the engine bay or yourself. It is quite a heavy item, but
easily manageable by one person. Once the manifold is safely out of the way,
remove the gasket from the cylinder head if it did not come off with the
manifold. Mine was stuck to the cylinder head, but it was easy to work free by
hand. Run you fingers around the whole area covered by the gasket to make sure
all remnants of it have been removed. Before fitting the new manifold, swap the
inner heat shield from the old manifold to the new one. This is secured by three
bolts of the same type that secured the outer heat shield (see above). There is
no torque setting for these, so tighten them firmly, but not too firm or they
will snap.
The studs stayed in the head when I changed my manifold, so I left them in
there and reused them as they felt in good condition (remember you cannot see
them - although you could use a small mirror). Removing them would probably be
quite difficult if they did not come out with the nuts.
Fit the new exhaust manifold to cylinder head gasket before fitting the new
manifold. Note it will only go on one way, so there is no chance of fitting it
the wrong way around. Simply slip it over the studs and push it up against the
head. This is easiest to do from under the car. Now you can fit the new
manifold. When handling it try not to bash it on the floor because being cast
iron it may crack quite easily. Carefully lift it up under the car and hook it
onto the studs in the cylinder head. While holding it in place with one hand,
fit the bolt to the bracket with the other hand. Do not tighten it yet. Now fit
the three bolts to the lower edge of the manifold to head joint but do not
tighten them yet either. Then, from above, fit the two nuts to the studs on the
upper edge of the manifold to head joint, complete with a washer each. Lightly
tighten these using a ratchet. Back under the car, lightly tighten the three
bolts on the lower edge using a ratchet. Now, using a torque wrench, tighten the
two nuts to 25Nm (as specified by Toyota ), then tighten the three bolts
underneath to the same torque. Finally, tighten the bolt to the bracket to the
same torque.
The final job is to refit the outer heat shield. Manoeuvre it into place from
below, fit the two lower and one centre bolts from below, and the three upper
bolts from above. No torque is specified so tighten them quite tightly, but not
too much or they will snap.
Now fire up the engine and you should find that the raspy tone and excess
exhaust smells have disappeared! When I did this I was alarmed to see smoke
rising from the manifold area, but I soon realised this was poorly aimed Plusgas
burning off, and it soon stopped.
NICK CHALLONER
