Exhaust manifold gasket replacement

[Martin Gutkowski <webmaster@xxxx>]

Hi All,

Seeing as Knut has provided a procedure on a task he has just completed, 
I thought I'd add one of mine. No doubt this will generate opinions on 
what I did wrong, suggestions for improvements, or things I've forgotten 
to mention. I hope this makes the tech section at DMCnews because I 
could have used an article like it. It's an expensive job in labour but 
where the parts are really inexpensive, so if you have the gumption 
(winks at Dave S), you might like to tackle this task.

I've read volumes on the DML regarding removing the manifold studs, but 
nothing about actually getting to them in the first place. Over the past 
couple of weekends, in lovely weather, I've been flat on my back under 
the back of my car learning how the exhaust comes apart so I could fix 
that "beetling" sound. If someone had told me what order to take things 
off it'd have been a lot of help. So here goes. (criticisms welcome!)

Firstly a general tip. When undoing 20-year-siezed rusty 
nuts/studs/bolts, try to apply only torque, that is rotation, and 
minimal sideways stresses on what you're undoing. Often this means 
holding the ratchet with both hands. A bit of penetrating oil is 
helpful, as is a wire brush to remove excess rust first. Another tip a 
friend gave me which I've never seen on the DML is when a nut is 
turning, but being very stubborn, try turning it back half a turn now 
and again.

Secondly: Do not attempt this job without a full compliment of tools - 
especially an extensive quality socket set with a good selection of 
extension bars.

Thirdly: Bits you'll need.

Manifold Gaskets
Manifold Studs (x12)
M7 nuts (x13) and washers (x12) (don't expect to be able to buy these 
easily if not using a DeLorean (or Renault or Volvo) facility.
Manifold-to-crossover gaskets (x2)
Catalyst-to-crossover gasket (x1)
Manifold and catalyst M10 mounting studs (x8)
M10 shake-resistant nuts (NOT nylocks) (x8)
U-bracket for cat-to-back-box

Note: If you do as I did and buy the studs from Volvo, you may find the 
studs are symetrical, unlike the OEM ones, which are longer on the 
outside end. This is fine except for one of them - the one that needs to 
have an extra nut to hold the starter heatshield - this is the 13th nut :-)

1) The first step is NOT to remove the back-box completely. Although 
this is possible on some cars apparently, it sure as hell wasn't on 
mine. However, you can start the removal procedure by taking off the two 
lower mounting brackets - un-bolt them from the engine. It's a 5-minute 
job to remove them and then the heat shield (asbestos remember - be 
careful). Once under the car it's obvious how they come off, and the 
rubber bushes just pull off. They can stay mounted to the brackets. The 
upper rubber bush should also be removed. This is on the pass side and 
accessible through the top of the engine compartment. Two M6 bolts 
secure this and it's a simple matter to pop it off. Also remove the 
U-clamp securing the catalytic converter to the back box. I broke mine 
doing this, so put this on the list of parts required before you start. 
The back box now hangs on the cat and the upper mounting bar, but in my 
case I did not have enough play to be able to slide the back box out of 
the cat.

2) Now the fun starts. Get under the car and locate where the exhaust 
manifolds attach to the rear crossover pipe. There are two studs on each 
side, both M10 with 17mm nuts. Both nuts are easy to get to on the right 
manifold, and the lower one on the left. The upper left nut is a pig. I 
found I could get to it with my 1/2" drive ratchet and regular socket 
from the top of the engine, going down next to the ballast resistors, 
and had just enough play to get one click on the ratchet! This is the 
only stud I broke due to not being able to hold it squarely. No matter, 
it's relatively easy to drill out, and I have an M10 tap, and soon made 
a new stud out of a fresh M10 bolt I had in the drawer. (when I took off 
the right manifold I soon saw why it broke - it's almost as if it was 
designed to! It's tapered at the point of greatest stress - I _assume_ 
through a poor manufacturing process)

3) Now the rear crossover pipe is free from the manifolds. This allows 
the cat to move and you should now be able to free the back box.

4) The cat is mounted to the rear crossover pipe with four M10 studs. 
Three of the nuts are easy to remove (I used my telescopic 45 degree 
wheel wrench to start them moving though). The fourth can be acessed 
only because the rear pipe is free. You should have enough play to be 
able to get to the fourth nut.

5) You can now remove the cat. The rear crossover pipe is free, but I 
couldn't work out how to actually remove it. I didn't need to, so I 
can't comment - it's just hanging there now waiting to be reattached! On 
taking mine off, all four studs were permanently siezed in the cat. If 
you are going to put the cat back, it's probably a good idea to remove 
the studs and replace them. I'm replacing the cat with Ed Uding's bypass 
pipe, so this wasn't something I did.

6) The cat heat shield can be taken off now by undoing two 10mm nuts. 
Asbestos again.

7) You can now tackle the left hand manifold. The nuts are 11mm and you 
should be able to remove all of them with various combinations of a 1/4" 
drive, a 3/8" drive and extension bars. Check your socket set has 11mm 
sockets in both 1/4 and 3/8 ! Some studs may well come out with the nuts 
- remember this as you're undoing them.

8) If the manifold doesn't fall off and hit you in the forhead, a couple 
of taps with a hammer will free it.

9) Stud removal. I have read a lot on this subject, but some advice from 
another (very experienced) friend seemed to contradict one important 
suggestion: Heating the studs. Do NOT take them to cherry-red because 
this affects the aluminium of the heads, and makes it brittle - doing 
this often results in the threads coming out with the studs, and 
re-tapping it makes it weaker still. I got all mine out with no problems 
using a combination of a blow-torch to heat the studs up, though not to 
red hot, then immediately liberally spraying it with freezer spray*. 
Then Mole grips (Vice grips) and my smallest super-wrench** got them out 
easily. I did not use any penetrating oil - take this as experience and 
not advice.

10) The right hand manifold is a bit trickier. You have to remove the 
starter motor, though not the alternator. The starter is held on with 
three 13mm M8 bolts which thread through the bell housing from the front 
of the car. They're relatively easy to remove. The starter can them be 
removed. It may require a lot of wiggling, and note that it is located 
by a roll-pin on the outermost mount. This may fall out when the starter 
comes out. Don't lose it, and remember to put it back (mine stayed put 
though - thanks to Walt for the advice). If you need an oil-change, now 
might be a great time, because the starter would come out a LOT easier 
without the oil filter in the way!

11) The heat stove has to be removed, which means removing the cold-air 
intake pipe. So too does the starter heatshield This is held on by an M7 
bolt and a spacer mounted into one of the unused manifold ports 
(rearmost), and an additional nut on one of the manifold studs (foremost).

12) With these removed you can now remove the right manifold and studs. 
The rearmost upper nut is a bit obscured by the alternator, I used a 
universal joint on a 3/8" extension.

13) Before replacing the manifold, clean up the mounting surfaces of 
both the engne and the manifold with some fine emery paper. It's also a 
good idea (and it looks nice) to clean off the rust off the manifld and 
paint with heat resistant paint. I bought a can of black exhaust 
manifold paint - nuff said!

14) Reassemble with lots of copper-grease. I found a tube of anti-sieze 
compound that "prevents seizure at up to 1100 degrees celcius". Seemed 
like good stuff to me. (made in Germany :-)

15) Reassemble in the reverse order.

* Freezer spray is an aerosol sold for use in the electronics industry. 
It's used to keep components cold which would otherwise overheat in 
order to troubleshoot a circuit. It's like a "backwards blow-torch" and 
cools things down very very fast.

** Bought a set of four of these at a car show ages ago. They have a 
kind of knurled tip and a sprung-loaded claw that reaches over the top. 
It's used for undoing rounded bolts, or pipes or..... manifold studs!

I have some photos waiting to go on the website.

Best Wishes

Martin
#1458
DOC UK