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Correct fasteners for Intake and Exhaust Manifolds


Namerow

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The two manifolds on the L24 engine are shown in the parts diagram to be secured with studs at all seventeen locations.  However, the engine in my 70 Z uses bolts for the top row (six locations).  A spare L24 engine (from a 72 Z that I had as my daily driver back in the 1970's) also used bolts for the top row.  I'm 90% certain that the head and manifolds on that car had never been removed for service (I was the 2nd owner and bought it in 1976 with only ~ 40,000 miles on the odometer).  The bolts used on both my engines show similar markings on the bolt heads.

Comments or insights, anyone?

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Interesting.  We now have a statistical population of two.  Anyone else with bolts on the top row?

BTW, a quick bit of on-line research suggests that studs are preferred over bolts in heavy-duty applications because clamping force is generated without any twisting of the fastener.  With a bolt, the clamping force can deteriorate under high, cyclic loads as the bolt loses that twist.  It's said that this is important for a cylinder head on a high-boost or high-compression engine working under heavy loads.  However, I don't see how it would apply to the case of the Z's intake/exhaust manifold duty cycle.

It was pointed out that studs create a different issue.  They can be problematic for engine installation and maintenance procedures, because the clamped part (the manifolds in this case) needs enough clearance above/next to it to let the part be lifted over the studs during installation or removal.  Unless I've forgotten something, I don't see that being an issue for the L-Series manifolds.

So, I'm still puzzled by the apparently intentional mixture of bolts (top row) and studs (all the rest).

Hard to believe it would have to do with saving costs (a stud set-up requires 3 parts, a bolt only 2).

And I don't see much difference between a bolt and a stud/nut when it comes to wrench access.

Maybe somebody in Nissan's Purchasing Department accidentally ordered too many bolts for another application and the Manufacturing people identified the manifolds as a place to get rid of them.

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The manifolds are secured by a total of 17 studs (or 11 studs and 6 bolts, depending on which camp you want to be in).

The Parts Manual lists them all as studs, but under 3 different PN's (with the related locations vaguely identified in the exploded-view diagram:

  • Type ‘12’ – 08214-82810 - 10 of (short) - includes the top-most row, where my engines have bolts rather than studs.
  • Type ‘13’ – 08214-83010 -   2 of ('shorter long') - one of these is clearly located in the diagram as the rearmost stud where the rear engine 'slinger' (hoist) plate is secured.

  • Type ‘14’ – 08214-83210 -   6 of (long)   - used in the locations where the thick 'yoke' washers are used to bridge the flanges of the intake and exhaust manifolds.

Notice how the Parts Manual says there are 18 studs.  In fact, there are only 17 studs used to secure the manifolds.  I'm assuming that one of the Type '13's is used somewhere else.

Here's the kit that MSA sells (my original studs are at the top of the photo):

102_5347.JPG

Notice the oddball silver stud (the one in the centre - no yellow zinc plating, different overall length from all the others, different length of unthreaded shoulder from all the others.

 

Here's a closer view of my original studs (the snapped-off stud came out of the engine slinger plate location, natch)...

102_5335.JPG

A couple of observations:

  • They all have the same threaded length for the end that screws into the head (makes sense, but easy to overlook during re-assembly).  The threaded length for the 'engine' end is shorter than that for the 'nut' end, which means that I've got the studs stacked wrong-side up in my photo of the MSA studs.
     
  • Once again, one of the 'long' studs is a little shorter than the others and has a slightly shorter unthreaded shoulder.  In this case I know it was not from the engine slinger location, but unfortunately, I didn't notice the difference in the long studs until I had them all out on the workbench afterwards, so I can't be sure where it came from.  It's possible that my snapped-off stud was also a 'short long' type, meaning that these are supposed to be fitted to both the rear-most and the front-most locations.  If that's the case, then the MSA kit is technically incorrect by supplying only one of them.  I don't think it's going to matter much for the front-most location, but I'm going to definitely fit my single 'short long' stud at the rear-most location to secure the slinger plate (I have a suspicion that it's made from a higher-strength grade of steel than that used for the plated studs).

Comments welcomed from any of our veteran or professional L-Series engine rebuilders.

Edited by Namerow
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These are the length measurements I've taken (by eye, using a metric ruler) for the Nissan OE studs that came out of my 70 Z's head.  The overall length for the studs supplied in MSA's kit is shown on the right...

image.png

 

The Nissan OE studs are ground flat on the inboard end (the end that goes into the head), whereas the MSA studs aren't.  You can see this in my photos.

My 'thread' and 'shoulder' length measurements should be considered +/- 0.5mm, because it's kind of difficult to decide where the threaded-to-unthreaded boundary occurs.

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I love these thread threads...

More to add to the ever growing hardware database.

The other engine studs that come to mind are:

2 M8's on the fuel pump mount

3 M8's on the "other" end of the exhaust manifold at the downpipe.

1 M10 on the alternator mount

8 M8's on the SU manifold

4 M6 on the fan clutch to water pump flange.

2 M8's on the clutch master, though those are special splined ones 

BTW, I feel remiss that I did not check my "bolts verses studs" on the upper 6 intake issue. I have 6 bolts on 3798

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  • 2 weeks later...
7 minutes ago, Namerow said:

So, growing consensus (4 owners!) that bolts, not studs, are correct for the top row of  manifold fasteners.  Now the still-unanswered question:  Why?

With bolts on the top row it makes installing the intake very easy. The big washers on the lower holes hold the intake in place while the bolts are installed. If there were studs everywhere it might be hard to slide the intake in place. I should know soon since I'm disassembling an L24 with two studs in the top row.

Chuck

 

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  • 2 months later...

I simply cannot believe they would have used 5/16 - 20. Sometimes an assembly trick is to make the two ends different so you cannot put something together wrong. But in that case, you don't make them just slightly different... You make them significantly different.

I gotta believe they are (supposed to be) M8 x 1.25 on both ends.  Do you have a 5/16 - 20 die that DOES fit?

I've seen stuff where the threads are stretched either from overtorque or years of differential rates of thermal expansion. Or maybe there's aluminum residue galled into the threads? Or maybe threadlock compound? Or maybe the crests are rounded over as an anti-vibration retention technique? 

Just tossing out ideas. Have you looked closely at the threads with magnification?

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So the bolts you removed from the head are M8 x 1.25 metric, but the threads in the head seem to be 5/16" x 20?  Maybe a PO (or mechanic) got there before you with the same goal of cleaning up the threads, but bungled the job by using a 5/16 x 20 tap.  The metric bolts might still 'fit' afterwards.

Still, I think it's more likely that your metric tap-and-die collection may have a 'visitor' from the SAE family that lives in the drawer next door :P

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