Editors note - "Back Box" = "Muffler"
Exhaust Manifold Gasket Replacement.
Update 5/6/03 Since
writing the original article, I’ve had experience of a car that was perhaps
more representative of the kind of condition other DeLoreans are in. My own car
had only 5000 miles on it and I did not encounter the kind of problems I did on
a friend’s “project car”. You can read about the fun we had at www.ourdelorean.co.uk
but if you’re reading this article to find out what to expect, note the
additions in red are following on from a manifold gasket job that really
didn’t go to plan...
This is an expensive job in labour but where the parts are really inexpensive, so if you have the gumption (winks at Dave Stragand), you might like to tackle this task. I took my time and got it done over three weekends, but I was enjoying the weather at the same time!
I've read volumes on the DML regarding removing the manifold studs, but nothing about actually getting to them in the first place. If someone had told me what order to take things off it'd have been a lot of help. So here goes.
Firstly a some general tips. 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. Also (particularly the exhaust manifold nuts) regularly check if the nut/stud you are undoing is getting hot. If it is, let it cool and move onto the next one. The studs are much more likely to shear as they get hot, and it's surprising how quickly this can happen.
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. A large knuckle-bar is also very useful!
Thirdly: Bits you'll need.
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 (you may wish to use the old ones) (x8)
M10 shake-resistant nuts (NOT nylocks) (x8)
U-bracket for cat-to-back-box
I recommend buying the M10 manifold-to-crossover, and
crossover-to-cat studs. On the second car I did, they all snapped
Note: If you do as I did and buy the studs from Volvo, you may find the studs are symmetrical, 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 :-) Make sure to note which one this is when you take it off.
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.
It _IS_ possible to
remove the back box without freeing the crossover pipe, but only by removing the
upper exhaust bracket completely, but this is fiddly and unnecessary, and it’s
really useful to have the bracket there to “hang” the back box on.
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)
I now have a LOT to
add to this! Firstly, the right hand manifold actually has 4 mounting points for
the rear crossover and there’s nothing to stop the other pair being used... if
the engine’s out of the car. There was a lot of evidence that the RH manifold
had been done in the past, and evidently out of the car because the crossover
had been replaced on the unused mounts, presumably because there were fresh
threaded holes as opposed to snapped-off studs! What wasn’t so clever was that
once in the engine bay, it’s nearly impossible to get to the upper nut. Nearly
impossible, but not impossible. I do not know how many DeLoreans use the other
pair of mounts, but be sure to check before setting a time limit on the job! It
took us 4 hours and removal of the coil to gain enough access.
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. The two lower of nuts are easy to remove (I used my telescopic 45 degree wheel wrench to start them moving though). To get to the third nut, you have to unscrew the lambda
sensor, which requires a 22mm spanner. The fourth can be accessed only because the crossover 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 cannot be removed without taking out one of the driveshaft. I didn't see any real need to remove it, so I jest left it there loose. On taking mine off, all four studs were permanently seized 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 replaced the cat with Ed Uding's bypass pipe, so this wasn't something I did.
The crossover can be
removed but it’s a real challenge in mental agility to find the one route
which will allow its removal – all others result in it not quite coming out by
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 drives! Some studs may well come out with the nuts - remember this as you're undoing them.
Make sure your sockets
are 6-point and not 12-point. A severely rusty nut can be rounded off by a
12-point a lot more easily than by a 6-point.
8) If the manifold doesn't fall off and hit you in the forehead, 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.
If only they were all this easy! If mole-grips don’t work, only try
a couple of times. DON’T chew up the stud with the mole grips. Your next best
bet is a proper stud extractor – the type that look like a large deep socket,
and not the large type with an offset hardened gear wheel to grab the stud –
they do not fit on to the upper row of studs.
If you chew up the stud first, the extractor may well not be able to
bite onto the stud afterwards.
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. You will need to remove the alternator if you have to get an extractor on this stud.
13) Before replacing the manifold, clean up the mounting surfaces of both the engine 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 manifold and paint with heat resistant paint. I bought a can of black exhaust manifold paint - nuff said!
Once the manifolds are removed, it’s an extremely good idea to take
them to a machine shop to face them – that is to skim a few microns off the
faces on a milling machine to ensure they’re all flat and line up with one
another. This has the added benefit of cleaning them. Any workshop worth their
salt will have no problem drilling out and re-tapping any snapped studs on both
the manifolds and cat at the same time.
14) Reassemble with lots of copper-grease. I found a tube of anti-seize compound that "prevents seizure at up to 1100 degrees Celsius". 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!
Editor's Comment: - Removing the entire engine
from the car makes this job much easier, and is not really all that much more
work. Plus its a good opportunity to really get in there and clean things up.
------ Dave S...
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