REAR MOST EXHAUST MANIFOLD STUD PROBLEM

[xfixer]

I am a (retired Automotive Tech 30 Yrs) and owner of a  mostly stored and used only in summer 62 K mile 1981 of a 280ZX turbo, t-roof, 2+2 with all factory loaded options since 1983.  I happen to be privy to someone named Joe who was one of Nissan's USA Nationwide Troubleshooters.  If a Z could not be properly diagnosed he was the tech they flew around the country doing the brainiac work.  I was informed buy him that the 280ZX had a problem where over time where the exhaust manifold would slide rewards causing the rear most stud to snap / shear off.  Also note that this is the same locator bolt that Nissan anchored the hook to lift the engine into the car during manufacturing. They were asking that little stud approximately 1/4" in diameter to do a man sized job.  Especially if the engine was dropped in with the turbo assembly attached.  None the less mine has sheared off causing an exhaust manifold leak and a subsequent exhaust noise.  Looking at where it is located and the amount of work involved I am wondering if anyone has managed to replace that broken stud without having to completely remove the intake and exhaust manifolds along with a lot of other parts too many to mention J  I am really good at doing what your not supposed to be able to do and doing it well however it looks to me as though I have my work cut out for me.  At 35 I would have whistled through the task at 68 the thought of the task has become daunting.  I wish to thank anyone in advance for any ideas, thoughts or assistance they may lend me regarding this topic.

 

Thanks Ray

 

xfixer@juno.com

[Zed Head]

_{Do you think the gasket is still in good shape?  Did you just discover it broken after hearing a noise or did you try to tighten the nut to fix a noise?  If you were fixing a noise then the gasket's already shot and a new stud won't help.}

 

_{Seems like drilling the stud end and trying an EZ-out is the only realistic option since you can only see the broken end of the stud.  Build a fixture to keep the drill located and perpendicular and you might have a shot.}  

 

_{​A slim possibility - if there's enough space in the hole a stud removal tool might be able to fit.  Basically a socket with internal teeth.  Drive it on and hope.  Overall, the odds are against you.  The studs can be hard to remove even with lots of room to work.}

[Patcon]

Galvanic corrosion can make it really difficult to get studs out after 35 years. You will still have to pull everything off to even get a grip on it....

[Namerow]

The failure of the rearmost manifold stud seems to be common to the Z L-Series engines and it's the bane of a lot of Z owners (i.e. welcome to the club).  Your ex-Nissan friend's statement that the cause comes from rearward shift of the manifold is interesting -- many have speculated on why this particular stud shears off, but I'm not sure I've ever heard exactly that explanation before.  In the end, though, 'why' doesn't really matter. You need a solution.  Because I have to deal my the same problem with my '70 (and I'm about the same age as you), let me think out loud for both of us:

 

Note:  Everything I say below is premised on the assumption that the stud is sheared off flush with the surface of the head, so that there's nothing left to grip on.

 

1. Solution #1:  Remove the stud using heat and an EZ-out.  As noted by Patcon, the intake and exhaust manifolds are going to need to come off.  Then you'll need to drill an accurately-centered/directed hole into a small-dia stud and use the smallest-dia ez-out in your toolbox.  From my experience, this is a certain recipe for disaster.  It's going to be hard to get that hole drilled accurately with the engine/cyl head still in the car.  I predict the end result will be an ez-out snapped off inside the stud. Now what do you do?
    
2. Solution #2: Forget about trying to drill a hyper-accurate hole and forget about using an ez-out, too.  Forget about trying to save the old threads. Just drill a reasonably accurate hole into the stud, then keep stepping up the drill bit diameter until you've taken out all the stud material and created a hole in the aluminum head casting suitable for tapping for a next-oversize stud.  I believe this is the most common solution, historically.  You may want to wait to hear what others have to say about this, though.
    
3. Solution #3: Remove the head and take it to a competent machine shop.  There's an element of trust involved in this approach.  You may end up with an oversize stud anyway (see #1, above).
    
4. Solution #3: Remove the head and try the ez-out strategy, taking advantage of better access to drill an accurate hole and apply directed heat.  Good luck with this.  I've recently tried to get a snapped-off mounting stud out of a Honda windshield wiper motor casting.  The stud has a 6mm thread.  The motor/casting was sitting on my bench in a vise, so I had perfect access.  I pre-soaked the stud with repeated applications of acetone/ATF for over a week.  I applied heat repeatedly for over two minutes.  I even tried cold-shock, using an aerosol spray-cold fluid.  Result:  On my sixth cautious attempt to get the stud to move, my name-brand ez-out snapped off inside the stud.  I might have had a better result using an oxy-acetylene torch for heat, but I don't have one (and it probably would have fried the wiper motor wiring anyway).
    
5. Solution #4: Remove the head and take it to shop that offers 'metal disintegration' services (also known as 'electrical discharge machining' or 'spark erosion').  Good news: You'll get to keep the original threads and stud size.  Bad news:  According to others, It's going to cost you $200 - $300.  Can anyone else confirm?
    
6. Solution #5:  Remove the head and replace it with a used one.  Z cylinder heads seem to be dirt-cheap.  Of course, you'll need to be sure that the one you get is straight and not damaged (check the cam lobes for good wear patterns).  It may need new valve seals (but then, the one on your engine may already need these anyway).

BTW, all of the head-removal strategies are going to require ponying up for the cost of a gasket kit.

 

Comments, anyone?

[siteunseen]

maybe you can read the part number from Nissan for the bigger one.  I think he said it was for their Titan pickup, been a few years since I bought one.  Seems like it was a M10x1.50.

 

I did the bit increment method then tapped the threads.

 

[Mark Maras]

 Has anyone had any success using an easyout extractor on this particular stud and are they ever loose enough to back out with a small center punch? If so, it would add credence to to shifting manifold theory. Possibly enlarging the stud hole in the manifold would prevent the stud from shearing?

 I have one I haven't dealt with yet. If it refuses to budge, my plan is to drill it out and install a heli-coil.

[Patcon]

Picking up a new head won't be a cheap option. He has a turbo car and those heads trade at a premium and then you would have to make sure all the hydraulic adjusters are good. I would remove the intake and exhaust, if there is enough to grab acetone/ ATF for a couple of days, hit the end with a hammer and try to vise grip it out. If it wont come out, remove the head and drill it out or take it to a machine shop for removal.

[siteunseen]

Well that went right over my head! Easy to do.

If it runs take it to a machinist.

[Zed Head]

My suggestions were about making an attempt before removing the manifolds.  Might get lucky.  For every five "took forever to get the broken stud out" stories, it seems like there is one "the stud came out with a reverse rotation drill bit without even using the EZ-out".  Take a shot then remove the manifolds to get the broken EZ-out and destroyed stud stub out.

 

Besides that, if one stud went, there are a few others close behind.  Check the front one.

[Mark Maras]

 What is the best way to remove a broken EZ-out assuming there is nothing to grab?

[Patcon]

The only way I can imagine is drill down around it until it's loose enough to get the piece out. Easy outs are hardened which makes working around them difficult.