Exhaust manifold gasket replacement V8 - anyone DIYed this?

[Will]

Hi, having got my 450 back from the garage at long last, everything looks great - but there's a bit of a blow from the exhaust somewhere, and a number of things are leading me to think it could be at the manifold (on the left hand side of a RHD car, if it makes a difference).  It doesn't seem to affect performance, but it does make the car a bit louder than I would like. 

Having just spent quite a bit at the garage, I'm wondering if anyone has replaced the manifold gaskets themselves?  From what I've read, it's either not too bad, or a real pain (with risk of snapping bolts etc) - but this has mainly been in relation to other cars that use the same engine but possibly have less room in the bay than w116s.  I've looked in the technical manual and it doesn't describe the process in full.  Any thoughts would be appreciated!

[UTn_boy]

You'll essentially have to take the motor loose from it's motor mounts and engine torque dampers, remove the metal engine fan and fan shroud, and then jack the motor up to get to all of the bolts/nuts that hold the manifold on to the cylinder heads.  The risk of studs/bolts breaking off in the cylinder heads is a chance you'll have to take.  Just be aware that if that happens the heads will likely have to come off to remedy the problem.  It's not a pleasant job, and is time consuming.  Regardless of what side the steering box is on, it is sometimes easier to remove the steering box, or at least disconnect it from the chassis and lower it, to gain access to the bolts/nuts on that side.

Something else to consider: the main reason the manifold gaskets give way is due to the manifolds themselves warping.  If you suspect that they're warped, then you'll further have to disconnect the header pipes from the manifolds so you can take the manifolds to a machine shop to have them decked/trued up. 

Take your time, proceed with caution, and use common sense to allow the car to talk to you.  Pay attention to how any particular nut/bolt feels when you're loosening it.  If it feels funny, then stop.  Again, it's not a pleasant job, but the end results are well worth it.   

[Will]

Wow, that's a really helpful response, thanks very much - even if the job itself does not sound too pleasant, as you say!  I think I'll be leaving this to the big boys to sort out, having read your notes its not the sort of thing I'd feel comfortable tackling on my driveway.  At least the parts themselves are not outrageously expensive. 

[marku]

That is obviously the way to do it and avoid some of the problems but as usual I didn't and simply went straight for the manifold nuts. The ones at the back are really difficult to get at particularly the one up against the brake booster but it can be done. Best of luck in trying to separate the manifolds from down pipes. I never did and ended up taking out manifold and pipe back to the centre box as one. No doubt it would come out easier by dropping it down but to make life difficult for myself I couldn't and took the assembly out of the top. This entailed removing the steering box for the right hand manifold. And yes I broke some of the studs but with the manifolds out it was possible to get a couple of nuts on and extract them. However two sheered off level and trying to use a stud extractor in a very difficult position broke the extractor in the stud. No choice but the head had to come off and go to a friend of a friend who had a spark eroder which got it out and a brilliant welder fixed a bolt to the other which came out easily. So you can do it properly or be prepared for all sorts of problems often solving one by causing another. Best of luck. 

[daantjie]

Oof just the though of the wrench dance that can be the outcome of this little exercise would lead me to take this to a pro.  Removing the ball joint from the front 6.9 struts was my limit for rusty part removal, and that was on the bench no less

[Will]

I'm definitely with you on that one daantje!  Especially after reading your write up, Marku...scary stuff.  But hats off to you for doing it and coming out the other side!    I'm  all for taking it to the pros, but first there is the cost, and secondly (and more importantly) it can be hard to find a genuine 'pro' for a 40 year old car.  The place I use 'seems' pretty competent, but I'll have to ask them about this.  In the meantime, while the car is driving well, I'm just concerned the blow may do some damage.

[ptashek]

I had this job done on my car, by a pro, and they're probably still cursing me to this day. At least one bolt sheared off and had to be drilled out.
I've done almost the entire suspension front and back myself, which is a "rusted bolt" hell, but I'd still probably not touch the manifolds myself.
But once you get new pins and copper nuts installed, it looks great, and is future proof. AFAIR the original bolts were steel. Not a good idea.