OM617 Intake/Exhaust Stud Questions - PeachParts Mercedes-Benz Forum

MSGGrunt · #1 07-15-2014, 05:37 PM

In rebuilding my turbo and replacing the intake/exhaust gasket while I'm at it I have discovered that the portion of the mounting studs that thread into the head is only about 9mm long. The threaded hole in the head is about 22mm deep and would allow the use of a stud with much more engagement so off I went searching....

Yes, I know a true stud would be the best solution, but would there be anything wrong with using a full length threaded bolt threaded say 20mm into the head instead of a mere 9mm and just cut the bolt head off and then clean up the threads with a die?

Any strength issues with using the strongest stainless bolts and matching nuts for their corrosion resistance or should I search for regular carbon bolts and order new copper washers?

What grade are the OEM studs?

Metric hex bolts - Bolt Depot

Bolt Depot - Bolt Grade Markings and Strength Chart

Stainless steel 18-8

The most common stainless steel for general hardware use.

Zinc plated class 8.8 steel
A tempered medium carbon steel. Class 8.8 is hardened, but it is not as strong as class 10.9. It is commonly found in automotive applications. Class 8.8 is similar to grade 5. Zinc plated for moderate corrosion resistance.

Zinc plated class 10.9 steel
A tempered medium carbon steel. Class 10.9 is stronger than class 8.8, and is commonly found in high strength automotive applications. Class 10.9 is similar to grade 8. Zinc plated for moderate corrosion resistance.

Class 10.9 steel plain finish
A tempered medium carbon steel. Class 10.9 is stronger than class 8.8, and is commonly found in high strength automotive applications. Class 10.9 is similar to grade 8. Unplated finish.

joeblack · #2 07-15-2014, 07:46 PM

I think 9 MM is a little short. I do not know what grade the original studs are. In my wagon, when I bought it the turbo was off but still with the car, nuts were missing. I kept the original studs but use stainless nuts. They hold up nice. If you only need to replace one I would stay with an 8.8 and use a stainless nut. I hardened stud would not stay hardened with the potential heat / temperature.

Did you rebuild your turbo because axial play or radial?
Did you measure your max boost pressure>

Mine has quite a bit of radial play and I would assume that the impeller is slowly grinding away.
I have haze of blue smoke and am wondering if the turbo is burning it .
Later J

mach4 · #3 07-15-2014, 07:59 PM

Quote:

Originally Posted by joeblack

[My turbo] has quite a bit of radial play and I would assume that the impeller is slowly grinding away.
I have haze of blue smoke and am wondering if the turbo is burning it .

Radial play is normal. The turbo is designed to run on a film of oil which allows the impeller to center itself. Axial play is a problem as that's where the seal is made. If your impeller were grinding itself away you wouldn't be able to stand the noise.

I can't see where blue smoke is due to the turbo.

Diesel911 · #4 07-15-2014, 09:03 PM

The Turbo will cause Blue Smoke if the Exhaust side leaks Oil.

when I pulled a Manifold Stud out of My Head it had enough room for 4 completet threads. I guess that is about 9mm.
I never thought checked to how deep the Hole was in the Head.

The Nuts on Mine were also Copper. I am guessing the idea is that they are not going to get tightened Much.

I did find that My Exhaust Manifold had some warpaged and had the fixed before I re-installed it.

Apparently longer Studs are not actually needed. You seldom read on Mercedes Forums where the 617 Engines have a Exhaust Manifold leaks.

MSGGrunt · #5 07-16-2014, 07:55 AM

I removed the turbo to rebuild it as oil, I believe, was leaking past the shaft seal and causing my car to smoke. I had no noticable play before I rebuilt it.

Yes, 9mm of thread engagement in the head is how much it is, only 4 threads. I only asked about longer studs as getting the copper nuts off probably will damage the threads on the stud and if I have to replace them I just figured using something that engages more of the threads in the head wouldn't be a bad idea.

Thank you Diesel911 for reminding me to check the mating surfaces for flatness.

I did not measure my actual boost pressure. I would like to shim the wastegate to get a bit more boost but, I would need advice on how thick the shims (larger washers) should be.

Dan Stokes · #6 07-16-2014, 08:54 AM

Do yourself a favor and avoid the SS bolts. Don't get my wrong - I LOVE SS and use them where I can. The problem is:
A) They're generally not very strong
B) They WILL gall, especially if they get hot. The next time you pull the nuts off you'll probably get the threads with them.

I'd trust the M-B fasteners. I'll wager they put a lot of thought into the best stuff to use for that. And I'm more than willing to alter the Benz stuff when it makes sense (look at my build thread if you don't believe me!).

Dan

ROLLGUY · #7 07-16-2014, 09:55 AM

Quote:

Originally Posted by Dan Stokes

Do yourself a favor and avoid the SS bolts. Don't get my wrong - I LOVE SS and use them where I can. The problem is:
A) They're generally not very strong
B) They WILL gall, especially if they get hot. The next time you pull the nuts off you'll probably get the threads with them.

I'd trust the M-B fasteners. I'll wager they put a lot of thought into the best stuff to use for that. And I'm more than willing to alter the Benz stuff when it makes sense (look at my build thread if you don't believe me!).

Dan

Agreed. Some things on these cars are over built/designed, and that is one reason for their longevity. If one bracket is good enough, MBZ will put three. As for the nuts, they are copper coated, not solid copper.

MSGGrunt · #8 07-16-2014, 06:15 PM

The other reason for an alternative is three out of the five studs are $50.00ish and the other two are $25.00ish.. I can't justify $250.00 for 5 studs unless they are delivered and installed by a beautiful Fraulein who also brings me a rack of Schneider Weisse Hefeweizen.

vstech · #9 07-16-2014, 07:31 PM

Quote:

Originally Posted by ROLLGUY

As for the nuts, they are copper coated, not solid copper.

Are you sure? I have seen several types, some that appear coated, and some that appear solid copper...

joeblack · #10 07-16-2014, 08:18 PM

Ok I misunderstood the original question. These are not the studs from the exhaust manifold to the turbo but the studs from the head to exhaust manifold.

I agree with SS studs/ bolts not being very strong also galling will occur when both the stud as the nut are stainless. some high temp nickel based anti seize can take care of this.
I personally would only use stainless nuts, as I did, and keep the original high strength studs.

Please let me know if the smoke issue is resolved because that is what mine is doing. First about 30 second after cold startup then less and when the motor oil is hot a continues blue haze. ( under normal load)

later J

Dan Stokes · #11 07-16-2014, 09:36 PM

If you NEED new studs don't forget that you can order them from ARP in pretty much any length. They won't be cheap but WAY cheaper than the prices quoted for the M-B stuff. And ARP's stuff is stronger than aircraft spec. I don't know if they have copper or copper plated nuts but they might well.

Dan

Simpler=Better · #12 07-17-2014, 09:15 AM

The nuts are supposedly red brass which supposedly hardens when heat cycles. They also don't rust to the stud, mkaing removal easy.

Nickle antisieze is an excellent choice as an alternative.

MSGGrunt · #13 07-17-2014, 08:08 PM

I can tell you one thing, whatever the nuts are made of it isn't some miracle alloy that allows them to come off easily. All of my studs backed out from the head instead of the nuts coming off.

I tried clamping them in my vice and still no luck. Maybe some heat on the nut will help.

I've also made the decision to reuse the factory studs.

Dan Stokes · #14 07-18-2014, 09:29 AM

Clamp them in a vise but you'll need an oxy-acetylene torch. In my experience a propane torch (like a Bernz-o-matic) doesn't have enough poop to do the job. Heat to glowing red-to-orange and be ready to start wrenching as soon as you take the torch away. As a knucklehead, I've done the heating and realized that I didn't have my wrench ready to do the deed.

I'm wondering if someone has been there before you and installed steel nuts. The copper (or copper plated) nuts shouldn't seize like that.

Also - I prefer the copper-based anti-seize if you can find it. The silver Permatex Anti-Seize is OK but not as effective as the copper-based stuff. I get mine at a bolt house, like Fastenal.

Dan

Simpler=Better · #15 07-18-2014, 03:54 PM

I've never had an issue with the studs backing out, except for the one closest to the firewall which always backs out for me.

Dan-have you tried Nickle based? It's expensive (~$16 on Amazon) but wild. I ran it on a gasser O2 sensor that previously melted aluminum anti-sieze paste.