Good info


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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

My early 71 (12/70 build date) has bolts on the top row of intake manifold.

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

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

 

Outside thread is M8 X 1.25

but

Is the inside thread into head 5/16-20?

 

 

Edited February 14, 20187 yr by 240260280

My 240z, HLS30-26074 from 2 '71,  has also bolts Original in the top row..

Thread seems to be Metric on both sides..   Latch them into each other, if the threads fit perfect, they are on both sides Metric! (M8x1,25 ?)

Edited February 14, 20187 yr by dutchzcarguy

My M8 X 1.25 die works on all of  the outside threads but not on any of the inside threads. 

5/16" = 7.938mm.   Difference is 0.78%

20 TPI = 1.27mm pitch.  Difference is 1.6%

Any chance a PO decided to force 5/16" bolts into the head, leaving you with a mongrel result?

Nope.  It is from an E88 head on a 260z. My M8 X 1.25 die will only fit the outside threads when chasing.

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?

I'll dig into another die set and see.  It seems very odd.