Let me provide a little background. I started having an exhaust leak from the front of the car. I discovered two of the four bolts that hold the exhaust mani to the turbo had wiggled loose. One was completely gone.

So I replaced those two bolts located more toward the block with brand new OEM bolts and washers. No problemo.

I figured while I was there I'd replace MN119784, which are the studs that go from exhaust mani to turbo as well. They are located on the side with the radiator support.

So I pull those two studs out and they are a bit rusty and corroded. No surprise there really and I go to put the new studs in. They will only go thread about three turns and will get stuck.

So I backed them out sprayed some WD40 in the threads and tried to clean up the original threads. I noticed that the new studs compared to the olds studs looked a bit different, so naturally I tried to see if the nut MD132930 would thread easily onto both the old stud and the new one. And they do without any problem...

So my question is if both studs can use the same nut without issue, why the hell can I not thread the new studs into the mani?

If A=B and B=C, then why the hell does A not equal C? Cannot Compute

Has anyone else replaced these studs with new ones and had a similar issue?

 

Get rid of the two studs and use two more through bolts instead.

 

Hmmmm...yah I have heard of evo owners doing this. Is there a particular reason Mitsubishi designed the mani to have two studs and two bolts? I'm trying to figure out what the benefit of this design was. My only thought was that the stud with nut on top might allow more expansion when the manifold reaches higher temps. That's just a guess though.

 

I went to 4 bolts vs. the factory 2 stud/2 bolt combo, because at that time, back when, I was swapping out several different turbine housings on my OS Green(9.0, 9.8, 10.5). As a result, I was pulling housings off every week or so to periodically test out different porting ideas.

The problem for me with the studs is that they complicate quick and easy removal of the turbine housing by itself. The studs don't make removal of the complete turbo too much more complicated. But, if you just want to pop the turbine housing off....it is way easier if you dont have to clear those damned studs.

I put about 45K miles on that Green with bolts sans studs and never had an issue. Keep in mind that another drawback with the factory stud arrangement becomes obvious if you should ever break one off inside the internally threaded housing flange. Then you will really wonder why the factory decided to go with studs as fasteners instead of bolts as you attempt to burn out the broken-off piece of stud with your acetylene torch. But, to each his own.

 

Yah funny thing is the studs that I have been running on there might as well be bolts. The nuts and the studs are pretty much stuck together, so when I was wrenching on them the nut and studs came out together. Another thing about the studs is they do have that portion in the middle without threads on it, and I imagine would be less likely to gall in the housing than the bolts which are threaded the whole way up.

I think I will switch to bolts next time and then remember to check on them every oil change. I can't believe I let them work themselves completely loose :/