The info is worth a bit more than .06 total.  I just may clean up the 3 studs for the exhaust pipe with a thread die and fix the very end tips which have no threads but seem badly deformed.  I thought that originally the studs may have had a small hex shape to install them into the manifold but not really sure.  I looked into the pipe and muffler kits that MSA offers and that looks to be the easiest and most economical solution.  I will need the extension pipe since my project is the 2+2 model.  Hopefully on Monday I can spend a little time on the broken EGR fitting on the exhaust manifold as well as the PCV valve rotted off on the intake.  The MAPP gas and the PB Blaster hopefully will do the trick before media cleaning the manifolds and then painting with some hi temp products.  Thanks again for the helpful hints.  The 2 mufflers originally on the car must certainly have been a restriction on flow.  Looking forward to the project challenge and learning experience on the Datsun Z.  John-Lugoff, SC.

 Many members, including me, have found a fifty-fifty mix of acetone and auto. trans. fluid to be an excellent penetrating oil.

2 hours ago, Mark Maras said:

 Many members, including me, have found a fifty-fifty mix of acetone and auto. trans. fluid to be an excellent penetrating oil.

Just keep in mind that it may have a shelf life, due to the acetone evaporating away over time (leave a small bowl of acetone out sometime and see how fast it vanishes).  Although I've used this DIY mix, I can only say that it doesn't work any worse than any of the other penetrating oils I've tried --   and it costs a lot less.  Overall, though, I had only limited success any of the penetrating oil (and WD40 is useless).  Fasteners that have finally been coaxed free using an impact tool showed very (very) little oil penetration below the surface, even after repeated applications and having sat for days beforehand.  I like heat (controlled) and impact (also controlled).

That's just my experience, though.  Your results may vary.

I had a bit of time this morning before going into work and did some clean up on the N47 exhaust manifold.  I will not trust the 3 exhaust pipe studs.  After cleaning ,what I thought may have been hex heads on the exposed ends of the studs turned out to be rusted through 10-15% of the diameter.  The areas right at the manifold are also rusted a bit thin.  So much for just cleaning and running a die to clean up the threads.  Definitely will need an oxy-acetylene torch for enough heat.  The 6 exhaust port mounting flanges really cleaned up nicely with just a touch of the angle grinder with a flap disc and finished with a 3M scuff pad.  I have a slight concern with the #6 port that the stud was missing / snapped off in the head.  I have no idea how long the engine may have been run like that-has not been on the road since 1995 according to the info when I purchased it last year.  The rear outer edge near the stud hole is either a bad casting or worn away by running with a missing stud.  The gasket was definitely gone in that area when everything was removed.  The rest of the gasket was all intact on the front 5 ports.  Can the edge be welded up and ground flat or just use a good quality gasket properly torqued.  The inner sealing area right at the port looks great as do the other 5 ports.  Just not quite as much flat surface for the flange as the #1 port has.  Looking for recommendations from the Z experts again.  This will not be a modified engine for performance.  Just a complete but budget friendly rebuild on the engine.  Quite a few stock parts can be purchased-timing components, water pump, oil pump, distributor, etc-for the cost of the aftermarket headers, but I will bite the bullet if the MSA headers are the only solution.  Thanks again. John-Lugoff, SC.

Good luck on the studs.  I used MAPP gas myself, just takes a little more waiting.  Check the back side of the stud holes, one or two of them might have broken through during tapping.  You can get a bit more thread penetrant in that way.  I had one stud that absolutely would not come out.  There was 1/4" left to grab on to.  I drilled a hole completely through it and squirted more rust breaker in that way.  It was one that would only move when the manifold was hot, even after several rotations.  It squeaked.  They key to removing broken studs is anger control.  So tempting to just say "screw it" and bust the remaining stub off with a twist.  Then you're really screwed.

Check that manifold surface for flatness.  It probably needs a resurfacing.  Don't remove too much, the retaining "washers" have to bridge the gap to the thickness of the intake manifold.

Just thought of another trick I've used to put in as little heat as possible, to avoid unintended damage like warpage.  Put tension/torque/compression on the tool used to do the pulling/turning/pressing.  Up to the limit before you think think things will be damaged.  Then apply the heat.  When there's enough heat things will move.

How does the egr tunnel under the intake manifold look? Mine rotted bad where the exhaust tube attached. Had to buy another intake. They had a recall on that connection. Mine obviously wasn't fixed. Hopefully your's was. There should be a sticker under the hood if it was part of the recalled VIN #s

Same vein - check the separator between the two sides, the exit tubes, in the exhaust manifold.  I bought a ZX engine and that separator was complete rotted away.  One giant cavity.  Make sure the parts are worth saving.

I also spent a bunch of money having a manifold resurfaced and a stud removed.  The guy went to the maximum of his estimate range (of course?), he couldn't let the broken stud beat him.  I paid the price.  Should have just bought a wrecking yard replacement.  Didn't know better at the time.

Patience is a virtue that the LORD has helped me develop over the years.  I will have to weigh out the options and prices of reworking the stock exhaust manifold-my labor rate is pretty cheap-vs buying a header.  Not sure about trusting a used header.  I have not really cleaned and inspected the intake at all yet.  I do know the PCV valve is completely rotted off.  Hopefully the threaded portion will come out of the intake easily.  Thanks again for the tips, John-Lugoff, SC.  I will not have any time the rest of this week to work on the project due to work schedule.

On 8/5/2016 at 5:23 AM, Namerow said:

I've had mixed success with freeze sprays.  Worked like magic in one case (frozen brake line connection), but failed miserably in another (snapped-off distributor clamp-down bolt).  In the latter case, I had the part on the bench and worked away at it for a week, using various sequences of heating, freezing, shock, and penetrating oil.  I finally had to drill out the remainder of the stud and re-tap the hole for an oversize bolt).  My theory (and that's all it is) is that the freeze sprays work well to break up ferrous-metal rust, but not so well to break up the thread bonding that occurs between dissimilar metals (i.e. aluminum casting / steel bolt).  Nevertheless, your results may be different -- and I hope they are!

One warning:  Freeze sprays are quite flammable, so be careful about spraying a part that you've previously heated with a torch.  You'll end up with a dandy little fire and you better have an extinguisher close by (ask me how I know this).

One thing with Freeze spays is that they work a lot better when a bolt or stud is not already snapped off. With stud or bolt intact, freezing is conducted through body of fastener and shrinks the fastener itself. When a fastener is snapped off, you generally end up shrinking both the fastener and the surrounding area. It works, just not as well.

You may be right about dissimilar metals as well, although I've found it works well on Marine applications with Bronze bolts and steel housings. But that's not the same as Steel fasteners in Aluminium... which can be an SOB.

Left handed Cobalt or Titanium drill bits are also a God send for removing broken studs and bolts. Spend the extra money and get high quality bitsl. And some cutting fluid... studs are usually very hard.

14 minutes ago, Chickenman said:

Left handed Cobalt or Titanium drill bits are also a God send for removing broken studs and bolts. Spend the extra money and get high quality bitsl. And some cutting fluid... studs are usually very hard.

I remember someone else promoting the benefits of LH drill bits.  I hope to give this a try sometime, but first need to buy a couple of them (not available at your average hardware store) -- prob. one for M8's and another for M10's.  One of my perennial problems, though, is positioning and then punching an accurate centre mark, and then keeping the bit from drifting out of it. I always seem to end up with a hole that's 10 - 15% off-centre.  Not sure if it's bad marking technique, bad punching technique, wrong drill-tip shape, or bad drilling technique.  Maybe it's all four!