Manifold to downpipe bolt specifications

[mdsalemi]

Anyone know the bolt specifics for the connection point at the bottom end of the manifold(s) to downpipe? There are six in total three on each side.

[Kevkeller]

You just need the size of the bolts?

[mdsalemi]

You just need the size of the bolts?

Yes. Just the size/length. They may be M8-1.25 (standard thread M8) and maybe 30mm long? Cannot tell without one in my hand…

[roymil]

Hi, I purchased a new set when a head bolt failed and I thought I would have to pull it.   I found another way so I had this new one to take a picture of.   

Yes, it's M8, but 50mm long with partial threads and came with special copper nuts.   The ones in your picture have more threads sticking out so they might be longer.

Now this is strange, when I went to check the bolts on the car to verify they looked like M8's, I found them all loose!  So loose I could easily spin all three.   Nuts seem seized to the bolts but both spin together.   What the heck?   I don't think I have an exhaust leak but wondering if I need to check that again, and if no leak, do I tighten or replace all the bolts or just leave it alone and pretend I didn't see that?

If I do try and fix something that aint broke, what torque?   And does this all have something to do with the copper nuts provided on the new ones?

As Rosanne Rosannadanna once said...."It's always something".   I hope somebody gets that ;-). - Mark

[Pawel66]

The bolts are definitely hex head M8 bolts, sorry do not have the length at hand. The MB part number for them is an "N" number, so they are not MB specific.

Nuts are definitely copper M8 nuts. The part umber is MB specific part number, not an "N" part number.

When I replaced my downpipe I had to re-tighten them after some time of use.

Perhaps, if in doubt, the simplest is to buy a new set at a dealer:

bolt    N 304017 008028, previously N 000931 008246
nut A 000 990 32 50, previously N 999901 008005

[mdsalemi]

Hi, I purchased a new set when a head bolt failed and I thought I would have to pull it.   I found another way so I had this new one to take a picture of.   

Yes, it's M8, but 50mm long with partial threads and came with special copper nuts.   The ones in your picture have more threads sticking out so they might be longer.

Now this is strange, when I went to check the bolts on the car to verify they looked like M8's, I found them all loose!  So loose I could easily spin all three.   Nuts seem seized to the bolts but both spin together.   What the heck?   I don't think I have an exhaust leak but wondering if I need to check that again, and if no leak, do I tighten or replace all the bolts or just leave it alone and pretend I didn't see that?

I cannot speak to our car specifically nor the factory specs, but some German cars in general. The nuts on the bolts are "one time use" copper plated steel, or at least that's what's commonly available from the usual gang of suspects across suppliers (not just MB). I say "one time use" because there is or is supposed to be some kind of crimp on the threads on the nut that cut into the bolt acting as sort of a locking device. So, with normal "grade 10"  (or the DIN equivalent) zinc plated steel bolts, with these copper nuts on them, once installed they will rust as everything steel does. High temperatures here make it worse. I suspect once you get these off, the only sane thing to do is replace them with new bolts and new nuts. Some of these available copper plated M8 exhaust nuts seem to have a flared washer style base. On my rear manifold, at least two of the three are loose enough to spin around. It's loose enough that I definitely have a leak here, bad enough that I initially thought my manifold was cracked due to my unfortunate muffler situation on the drive to PagodaFest.

I was able to sneak a caliper on on one side and my existing bolts are 70mm long. That leaves a LOT of exposed thread, perhaps too much for convenience in getting a wrench on it. 60mm seems like a better choice. Our friends at Authentic Classics list the bolt as 50MM in length which to me looks like it may be a bit too short for convenience in installation.

What precipitated the question initially yesterday was my need to replace the center section of the muffler system. Mine's a Time Valve, so the stainless steel system consists of these parts: manifolds, downpipes, center section with first muffler, rear section with rear muffler. I tried to remove the rear section and it wouldn't budge; beyond my "working in the driveway only w/o lift" capabilities.

I made arrangements with a mechanic friend here familiar with the cars (he is an engineer for one of the NASCAR teams here) to take care of in December, and he said get new bolts and nuts and the donuts between the manifolds and downpipes.

I have a mind to replace the bolts with stainless steel. If my memory serves me correctly on my BMW 320i the bolts were stainless with copper/brass nuts, or everything was copper/brass and came apart super-easy when I had to change the muffler once. (in my driveway w/o a lift!)

Comments on any of this welcome!

[wwheeler]

A couple of thoughts here:

Mercedes was fanatical about bolt length. If you look at what the factory used, a screw or bolt had very little exposed on the backside. The bolt or screw was always just the right length and no more. I figure that is to prevent corrosion on the exposed end and then dragging that corrosion through the threads upon removal. So Mercedes had an arsenal of bolt sizes they used. Contrast that with the Plymouth I have - most bolts stick way out from the threads. More isn't always better.

Stainless is significantly softer than a rated steel bolt. I would be a little worried about using those on the exhaust pipe to manifold connection.     

[mdsalemi]

...Mercedes was fanatical about bolt length. If you look at what the factory used, a screw or bolt had very little exposed on the backside. The bolt or screw was always just the right length and no more...Stainless is significantly softer than a rated steel bolt. I would be a little worried about using those on the exhaust pipe to manifold connection.   

Yeah, I get it. However, not everything Mercedes did was 100% flawless. They surely didn't envision people taking their cars apart 50+ years later, after the fact. On this exhaust system design, I mean really--what purpose is served by a fully welded OEM system? My stainless steel TimeValve system, along with many other aftermarket units, is modular. Ran into a similar kind of issue on the drive shaft, when the OEM style features non-replaceable U-Joints. Thankfully the rebuilders on that were able to install replaceable U-Joints. There's a difference in designing for manufacture and designing for service. Clearly my 70mm bolts now are way too long. Maybe when installing the OEM 50mm long ones, the mechanic may wish for an extra few MM...

Indeed both 304 and even 316 stainless is softer and not as strong as carbon steel in any grade; no argument there. And, if you don't know what you are doing with stainless you run the risk of thread galling--just as bad as rust. I confirmed with a reliable exhaust expert that using stainless steel on the manifolds to downpipes is acceptable. I've got copper plated exhaust nuts ordered as well as a selection of bolts. I suspect that my rusted steel bolts on there now will have to be cut off, which is a royal PIA as it's a very tight space in which to work.

I've managed to locate a guy (local engineer/mechanic with Joe Gibbs racing who does work on the side and does have some familiarity with our cars and older Benz in general) who will take my car in and hopefully get my exhaust back together in a few weeks.

[Pawel66]

Why welded exhaust system? I thought it may be durability. Cost perhaps.

[Benz Dr.]

The bolts are definitely hex head M8 bolts, sorry do not have the length at hand. The MB part number for them is an "N" number, so they are not MB specific.

Nuts are definitely copper M8 nuts. The part umber is MB specific part number, not an "N" part number.

When I replaced my downpipe I had to re-tighten them after some time of use.

Perhaps, if in doubt, the simplest is to buy a new set at a dealer:

bolt    N 304017 008028, previously N 000931 008246
nut A 000 990 32 50, previously N 999901 008005

Nuts are copper plated. Copper would be far too soft to torque down enough to prevent leaking.

[Pawel66]

Yes, sorry - too much of a shortcut.

[mdsalemi]

Nuts are copper plated. Copper would be far too soft to torque down enough to prevent leaking.

So hear's a question. Is that "ring" or metal donut between the manifold and downpipe a one-time use thing, like a "crush washer" or is it something that can be re-used? Does one use any kind of sealing paste with it?

[Benz Dr.]

Any crush type of seal or gasket would be a one time use only. Think head gasket or intake manifold gasket.

[Baybear]

I have the TimeValve stainless exhaust on my 1971 as well. I measure the bolt going from the exhaust manifold to the downpipe at 57mm. This is from the top of the bolt to the bottom of the bolt So you need to subtract the the thickness of the head which I imagine is about 4 to 5 millimeters. There is a significant amount of thread showing on top of the tighting nut, which I estimate at about 7 to 8 mm. So a 50 millimeter bolt in length should be about right.
Will

[wwheeler]

The gasket between the downpipe and manifold that Mercedes supplied me with was a graphite impregnated material sometimes called Grafoil. https://www.neograf.com/products/gaskets-sealants/grafoil-flexible-graphite/

I doubt it could be used again and mainly because it will be destroyed upon removal. The material won't degrade though. 

[mdsalemi]

I have the TimeValve stainless exhaust on my 1971 as well. I measure the bolt going from the exhaust manifold to the downpipe at 57mm. This is from the top of the bolt to the bottom of the bolt So you need to subtract the the thickness of the head which I imagine is about 4 to 5 millimeters. There is a significant amount of thread showing on top of the tighting nut, which I estimate at about 7 to 8 mm. So a 50 millimeter bolt in length should be about right.
Will

Hello Will,

Yes, 50mm seems to be the consensus on the OEM bolt size.

Mine measure about 65-70mm, and one can see from the photo I posted that there's a LOT of excess thread exposed. Wallace has pointed out that MB was rigid in thread length, so if all is put together properly, 50 mm should do it. However, I opted to add a few and chose 55 mm bolts. Nothing wrong with a few mm of thread hanging outside.

So this one instance I had with my exhaust donut failure has begat a much larger exhaust system refurbishment.

1. I lost my chrome tips as soon as the system hit the pavement; VEP had a set at PagodaFest so I got them there.
2. I ordered all new rubber donuts when I returned home.
3. I discovered that I never had the OEM heat shields in place, no doubt this contributed to the early death of the rubber donuts, so ordered a set of those.
4. I discovered that holes had worn through a pipe and the first muffler; ordered a new center section from TimeValve.
5. One of the SS clamps has damaged threads; ordered a new set of SS Clamps.
6. I had temporarily patched the exhaust holes with some exhaust goop; the exhaust still was leaking and discovered loose bolts at the manifold to downpipes connection. Ordered new bolts, new copper plated steel exhaust nuts, new SS bolts and new steel bolts in case the SS ones fail at some point. Also ordered the new sealing rings for this manifold to pipe joint.
7. Despite my best efforts with limited resources, I was not able to get the rear muffler off the center section, so had to raise the white flag.

One of my friends here is an engineer and mechanic with Joe Gibbs Racing, and I asked him for some help. As soon as he is done with another project on his lift, he'll tackle mine.

Even on a lift, rather than using all kinds of mechanical and other forces (heat, flame, hammer, etc.) to try and separate the joined pieces of the exhaust system, he may decide it is easier to just drop the entire system, and separate it off the car where you don't have to worry about damaging anything on the undercarriage.

Hoping I can get my car to him in the next few weeks.

[Pawel66]

Please note you will need a very high lift to manage out the front down pipe and to install it back. Even if you separate it from the central section.

[mdsalemi]

Please note you will need a very high lift to manage out the front down pipe and to install it back. Even if you separate it from the central section.

This is on a traditional automotive service lift. I don't know how high they go, maybe 2M?

[Pawel66]

It is surely enough for front pipe, not sure if it is enough for the entire system removal. You need to point it downwards to maneuvre out the front pipe.

[mdsalemi]

It is surely enough for front pipe, not sure if it is enough for the entire system removal. You need to point it downwards to maneuvre out the front pipe.

Will let the engineer figure out the best way for removal. "not his first rodeo" as they say.
After removal, no matter how, it will be separated and re-assembled piece by piece starting at the manifold...

[Pawel66]

Well, then perhaps you can just cut it if need be. Enclosing pictures from my front pipe replacement. I went to nearby Mercedes dealer, I was with the mechanics working on the car in their service area (which, by the way, is available for customers to walk in if they want to). I brought my fender protector, my screws, nuts, washers etc. (as they would not have cadmium plated ones, certainly .

I did it on several occasions - showing them step by step procedures form BBB, e.g. for front suspension work.

[mdsalemi]

Well, then perhaps you can just cut it if need be.

Cutting pipes is the last thing we want to do. It's all stainless, a TimeValve system in four parts. If anything is cut, it is destroyed and then needs to be replaced, meaning new pipes. My goal is to remove the damaged piece from the system and replace with the new. The front pipes, and rear muffler will be retained. I surely hope this isn't the case that cutting is involved.

[Bshaunessy]

Michael Salemi
  Further to PAWEL comments RE difficulty in removing complete exhaust system.  His cautions are absolutely correct.
     I recently ( DIY) removed the OEM fully welded, complete exhaust system , including the downpipes.   I was able to maneuver sufficiently to get entire system out  in one long piece by using my lift at full height (2 meters…..it would not have come out if lift was any lower…..removal, as its one piece, is very difficult).
   I replaced with an aftermarket set of downpipes, crossover section, resonator and rear muffler….all from BUDS BENZ…( all carbon steel) ..all bolt up except down pipes and crossover to resonator which I had to weld.
   You are replacing just some components in your TIMEVALVE stainless system so you will need some stainless welding.  CAUTION: the downpipe to resonator connection is likely a weld joint (?) and the geometry here is critical.  Requires downpipes to be fully installed and then the resonator tacked in place to get the angle right AND then removed from car and bench welded ( stainless in your case) and then re-installed on car ( so you meed a couple sets of crush gaskets for downpipes to manifold connection.
   If geometry of downpipe to resonator is off by just a bit, some parts of system downstream will rub on frame and you will have to cut and re-weld. ( ask how I know!)
   THIS IS DEFINITELY A DIFFICULT JOB…..best to have a muffler shop that has experience with stainless systems and welding perform ( no muffler shop within 4 hours of where i live….hence DIY)

[mdsalemi]

OK, remember my well meaning friends, I threw up the white flag already and am leaving this in the hands of an engineer-mechanic familiar with working on many cars of all kinds. He just built and raced in the La Carrera Panamericana race in an old Porsche he fully rebuilt. He works for Joe Gibbs Racing. I trust that he will figure out the best way to do this, and if he finds it beyond the scope of his equipment or himself, with all the custom exhausts and race cars here (this is NASCAR country) I am certain someone would be able to take over in the event he too, raises the white flag.

Now, that being said: he does have a conventional automotive lift. That's a plus along with his tools.

Remember I have a TimeValve system, all stainless steel. The new part just fabricated for me is the center section, that's between the ends of the front downpipes (that come from the manifolds) and before the rear muffler assembly. It's the largest single piece in the entire system, measuring nearly 2M in length, and it's all welded together and delivered as one piece. At the leading edge of this assembly, the joint is a sleeve joint with female ends welded onto the stainless tubing. The male end is the downpipes; they were designed to slide together, and these are clamped, not welded together--though welding is an option for those so inclined. The tubing measures precisely 1.625" (English not metric measurements) and there are four clamps in the system. Two of these clamps, also stainless, are at the downpipes to center section joint. At the far end of the center section, the pipes are male (plain) ended. They slide into the identical female ends welded onto the pipes coming out of the rear muffler. At this joint, there are also two additional stainless clamps.

If there are any welds that the initial installer did 20 years ago, these could only be tack welds and they would be hidden. No fillet welding of any kind except on the as delivered assemblies from TimeValve, none on the joints. There doesn't seem to be any reason to both weld and clamp a system like this. You either weld it for a clean look, or you clamp it. Both? Why would you do this? I just confirmed with TimeValve that as supplied, welding is NOT needed; it's up to the owner/installer. Clamps will do the job.

I had no prior rubbing of any exhaust parts on the frame, or any other part of the car. It was fine as installed 23 years ago. I hope I can get it back without too much effort.

I will be reporting back with the results of the next phase, when the project gets handed over to the engineer/mechanic.

[mdsalemi]

Here’s the rear joint. Shows female sleeve from rear muffler and male pipe ends from center resonator assembly. Clamped. Identical joint at front end of resonator center assembly, with clamps. Picture was taken with clamps loose, with hanger removed, and with wheel removed.