Dropping the clutch for launching will have to be handled by my other Z - when I am in that mood 😉.  I have a replacement engine for that one sitting on a stand and a few other upgrades planned before I can fire that beast up again.  It will be worked on this year for sure.  

 

This is the old engine, which I broke at Road Atlanta back in August of 2015:

 

This is the new one:

    

 

This new engine is very similar to the one I destroyed.  Changes include an 89 mm bore, (is now a 3.0 liter vs. 2.93 before), same cam and valve train except intake valves are titanium this time and were stainless steel before.  And this time the crankshaft not lightened and knife-edged, but it is still offset ground and combined with eagle rods to get to the 3.0 liters.  This new engine will utilize a dry sump oiling system.  

But, I digress...
 

 

Edited February 6, 20241 yr by inline6

3 minutes ago, inline6 said:

This is the old engine, which I broke at Road Atlanta back in August of 2015:

How did you destroy it? These engines are normally pretty robust...

I will never know for sure.  However, I got the timing chain off by one tooth (it has a Kameari chain tensioner set up) and the valves contacted the tops of the pistons for a few minutes upon start up while it was like that.  I corrected it, and went to Road Atlanta for a track day a week or so later.  During the fourth and last session, I had a rod bearing, and then rod let go at over 100 on the main straight.  That block had holes on both sides when I pulled it out. 

According to another Z racer, turns 6 and 7 do a number on cars that run there.  He has an Accusump in his Z (and an 8 qt Nissan Competition oil pan like I was running) and he said he sees the Accusump "working" on that part of the circuit, meaning oil pressure is dropping under the high G load.

Edited February 6, 20241 yr by inline6

Lack of oil could definitely do that!

On Sunday, I took the diff back apart and reassembled it with .020" of additional shims instead of going back to the .015".  The reason for the change?  I just figured I'd learn more if I tried something I had not before.  

First, one pic showing the wipe pattern on both drive and coast sides at the same time with the .030" of shims:

 

Note the wipe patterns are offset.  You see it is to the left on the coast side and to the right on the drive side.  Ideally, the contact would be in the same area on both sides of the teeth.

Now a pic after switching to .020" of extra shims:

 

Ha HA!  This is better.  With .020" of extra shims, and the .3 mm shim on the left and .4 mm and .5 mm shims on the right, I measured .009" of backlash.  When I tried to switch the .3mm shim to the right with the other two, I noticed that everything was bound up as I was tightening the side flange bolts.  I was careful to not tight them all the way as it was clear that I had zero backlash.  So...

I think I am very close to the correct pinion shim size now, but I am thinking I may need to alter the side flange shims a bit to get the backlash within factory spec.  Time to order some more side shims to experiment with.

More pics of contact pattern with .020" of extras shims - I have been putting the paint on thinner so it is easier to see the pattern:

    

    

Yellow vs Prussian blue marking compound

My local auto parts store only had Prussian blue. I tried it for marking my ring gear but it seemed to be difficult to observe a contact pattern. Would yellow of been a better choice?

Perhaps.  You can try taking close up pictures and using zoom to see if that helps.

https://www.amazon.com/Genuine-Fluid-1052351-Marking-Compound/dp/B00BK7MFC8/ref=sr_1_1?crid=N3OUSAPOE5G6&keywords=yellow+gear+marking+compound&qid=1707305463&sprefix=yellow+gear+marking+compound%2Caps%2C133&sr=8-1

That is the one I got.

 

Another round.  This time, I only shuffled some side flange shims.  I removed the .3 mm from the left side and replaced it with a .2 mm.  Then, I swapped out the .4 mm on the right side for a .5 mm.  So, the right side has 2 .5 mm instead of a .4 and .5 mm.  So, with the OEM shim, + .020" of extra shims and the side flange shims as just described, the back lash was a touch over .006".

I put the marking compound on thin again with brush strokes the same as before:

  

One pic showing wipe patterns on both sides of the ring gear teeth:

 

And the rest - note that beyond the obvious displacement of the paint that reveals the tooth surface, the brush strokes are "erased" further out, indicating possible tooth to tooth contact there (or super close proximity) as well.

    

      

    

    

The contact patterns are looking very close to optimal to me.  I think I need to experiment with something between .015" and .020" of extra shim thickness to see if I can move the patterns on the drive and coast side to be closer to the same contact area on the tooth.  Right now the coast side is a bit more towards the heel and the drive side is a bit too close to the toe.  

I hope pressing the bearings on and removing them from the pinion gear this many times is not causing any issues.

Edited February 8, 20241 yr by inline6

Those patterns look great, your diff should run very quiet.