Correct fasteners for Intake and Exhaust Manifolds

[Namerow]

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?

[jfa.series1]

Same set-up on my engine.

[Namerow]

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.

[240260280]

My Nov 69 has bolts too.

[Namerow]

That does it!  I'm putting the bolts back in the top row.  Anybody want to buy six brand-new, never-used MSA studs?

[beermanpete]

All the Z engines I have worked on have studs in all positions.

[x911]

3 hours ago, beermanpete said:

All the Z engines I have worked on have studs in all positions.

Were they all the same length? I've read that there are 42mm and 47mm studs? 

[Namerow]

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):

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)...

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 November 5, 2017 by Namerow
corrections and additions

[german240]

 @Namerow thank you very much! Could you do me a favor and post the dimensions of the short and long bolts (the MSA kit)? 

[Namerow]

I'll measure and post later today.

[beermanpete]

20 hours ago, x911 said:

Were they all the same length? I've read that there are 42mm and 47mm studs? 

I do not know what the lengths are.

[Namerow]

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...

 

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.