Hi all,

I've just received my 1973 240z! The previous owner towed it out from MO for me along with piles and piles of parts. We went over it together and it's in better shape than I expected (it was a Craigslist transaction over the phone between MO and NJ).

I'm sure that I'll start finding nasty surprises once I start into it, but for now I'm basking in the glory of having a Z in my garage.
 

 

Edited May 27, 20159 yr by Matthew

I agree with the assessment about the plastigage. How far out were those two rod ends? Couldn't have been much!

So how was it when you turned the crank with (almost) all of the pistons in there moving up and down? The hiss of the new tight rings sliding across fresh sharp crosshatch? Exhilarating? Give you chills?

All this talk about bore measurement and the like... Reminded me of this old guy resting in the bottom seldom used recesses of the toolbox. I don't know when was the last time he was pulled out for any reason other than to just admire him:

Oh, wow, Captain!

That is a beautiful bore-mic. Probably still as accurate as it was when new, and I'll bet you're proud to own it. 

I didn't ask the machinist what the rods were off by and since I couldn't be as accurate as he with the tools I had, I had to go with the re-fit. Even if I had him leave the big ends together so I could measure them, I don't have a rod vise to hold the big end while removing the nuts. I probably could have used a vise without serated jaws, but there's no sense taking a chance on twisting the rod. The important thing is that when it all went together the plati-gauge crush was good and the crank spun freely.

We didn't post these shots before because we want to keep the number of pix down to ten or less... Here are the orignial measurements for #5. Please correct me if I'm wrong, but I read that as somewhere between 0.0015'" and 0.002", according to the plasti-guage wrapper -- still within limits according to the Assembly Manual but it certainly locked up. 

You're right about the sound, too. With all six cylinders filled, now, the difference in effort to turn the crank is barely noticeable, between four and six; the whole assembly turns over easily with one hand. I might take a running-torque reading but I wouldn't have anything to compare it to if I did. Besides, that reading wouldn't mean much with larger diameter cylinders, shorter pistion skirts, and thin rings -- nothing is stock.

Know where I can find a figure to compare to?

I wish Matt was here to be in on the build. 

 

Edited February 16, 20178 yr by Takhli
spelling correction

I'm probably the last person on the planet to figure this out, but I was thinking some more about the geometry of the plastigage and what happens when you crush it. As you decrease the thickness and extrude that material into additional width, the change in width is non-linear. The amount that the width changes will go up faster as the thickness decreases:

You can see this phenomenon in the reference stripes on the plastigage package. I'm sure you already knew this, but for example, that's why the width change between .003 and .002 is much smaller than the width change between .0015 and .001.

I do have a point though, and that point is that you are much closer to .0015 than you are to .002. Still within spec though, so the binding is curious. Of course, the whole spec is only applicable to a crank that is perfectly round, a rod that is perfectly round, and bearings that are perfect consistent thickness in every location. Any high spot or oval anomaly anywhere could miss the gage, but cause the bind. It's too bad they haven't come up with a plastigage that allows you to spin the crank WHILE the plastic is in there and still get an accurate reading. There's a product idea for you. 

Not that it matters now, but I assume you tried that rod in other locations and the issue followed the rod? I also assume you tried swapping the rod bearings around and same thing. Didn't follow the bearing, but followed the rods?

About a torque spec for the force required to spin the crank, I'm not aware of anything.

On 2/16/2017 at 8:48 AM, Captain Obvious said:

 

On 2/16/2017 at 8:48 AM, Captain Obvious said:

"...the whole spec is only applicable to a crank that is perfectly round, a rod that is perfectly round, and bearings that are perfect consistent thickness in every location. Any high spot or oval anomaly anywhere could miss the gage, but cause the bind." 

"...I assume you tried that rod in other locations and the issue followed the rod? I also assume you tried swapping the rod bearings around and same thing. Didn't follow the bearing, but followed the rods?"

Good point, Captain.

If I recall correctly, number 5 locked up after about 45-degrees rotation and was free when I turned it back past BDC, for some period. And although number 6 was similar it never really "locked up"; it just became very, very tight, until I decided it was too much. 

As far as swapping the rods into other cylinders - no, that didn't happen. However, I did try swapping the bearing inserts but it didn't help much. I could turn 5 a little more but it still locked up. By the time I finished trying number 6 installed and torqued it was late and I figured that I should make the next decission after a night's sleep. In the morning I decided to run the tow assemblies into the machinist for inspection.  

Glad you mentioned it though; that was a good reminder.

 

On 2/16/2017 at 8:48 AM, Captain Obvious said:

 

 

I need to change course a bit here, and ask a question about modifying the P90a for mechanical rocker arm pivots...

If anyone knows of another thread on the fourm talking about this, please let me know.

Question 1: Is there any known history of Time-sert failure?

Reasoning: There are only about three threads of at the base of the rocker arm pivot post where a Time-sert is also supported by cylinder head material.

It seems to me that under continuous load - especially with high-lift, longer duration cams requiring heavier valve springs - this is a weak point in the Time-sert, where radial cracking might occur, over time. Correctly installed, the Time-sert is not neccessarily flush with the top of the cylinder head so the installed rocker pivot may or may not provide additional stability.

Question 2: Should the unthreaded area between the Time-sert and the cylinder head be filled with an industrial aluminum epoxy filler, to help support the Time-sert?

I've included a few photos to help explain.

Thoughts on this please...

Shown above is the rocker arm pivot post boss on a P90a cylinder head, designed for hydraulic pivot posts, as we know. The unthreaded depth of each boss is aproximately 0.550".  

Here, above, is the 27mm long 20-1.5 x 18-1.5 Time-sert used to adapt the P90a to solid pivot posts; I believe a shorter insert is also suitable because the hydraulic pivot post does not reach a 27mm depth, as the Time-sert does.

In the thread depth comparison above you can see that a mechanical cam pivot post base does not extend to the full depth of the Time-sert,...

 

Here is a measurment comparison of the three components, with the caliper representing the unthreaded depth of the boss.

 

 

 

 

Edited February 18, 20178 yr by Takhli
Photo editing

I haven't messed with any of that stuff so I don't have any experience, but I agree that seems a little hokey. With a little web searching, however, it does seem that's the "accepted" solution, and I didn't see any records of failures.

Do you know if the Timeserts hardened?

Other than the obvious (and expensive) solutions of boring and rethreading or sleeving the entire hole, one other idea instead of epoxy would be to turn (and maybe even thread) some aluminum spacers to take up the gap? Loctite to hold them in place in the upper portion of the recess?

Hi, Captain...

Matt and I are doing some research on the inserts today, and tomorrow I'll call the maker about the insert's hardness. Maybe it isn't a poblem because, with the pivot post holding the assembly in the hole, the insert sees mostly compression forces rather than shearing forces.  But I agree... It seems a bit "hokey".

I like your idea of a threaded aluminum sleeve but rather than machining the entire depth of the hole, maybe have it thread onto the pivot and slip into the hole. We could secure the sleeve to the head with green locktight to keep it in place. Still expensive though; I'll need to look around.

Also, I think it's interesting that this modification has been around so long and there's hardly any mention of pluging the oil delivery ports. Seems to me that there will be some oil seepage beneath the pivot post if the port isn't plugged. 

Actually the timesert will be under tensile force after torquing, pulling up on the cylinder head threads.  And the seating surface of the pivot on the cylinder head, after torquing, should prevent rocking or side movement.  That's probably the most important consideration.  Be sure the timesert is below the surface of the head after insertion.  The pivot should't seat on the top of the timesert.

This off current subject but Matthew couldn't see a picture I posted a few weeks ago so I took another.

 

I learned something this weekend:

After setting up all the chemicals I bout for this gas tank restoration, I have determined that a) the Por-15 reconditioning kit doesn't work, muriatic acid is scary, c) either the water in my neighborhood is too hard or rinsing with water is stupid, and d) you only need three things to do the inside of your tank.

I tried all kinds of combinations of stuff, but everything said to use hot water to flush the tank, and that cause instantaneous flash rusting.



I also learned that every piece of protective gear I've ever bought leaves this spot on my neck exposed:


So after three tries I finally found the holy grail of steps to get this done: one pint of muriatic acid for three minutes will totally clean the interior of your tank, then rinse it with a pint of acetone, then another pint of acetone, and then another pint of acetone, and finally one can of Red Kote. The key thing here is that acetone is 100% compatible with Red Kote so you don't have to dry it out. This makes the sealing process take approximately 30 minutes. Follow the instructions on the RK can and you're done.





The do the outside in Por-15 and put it into the car (or storage like me).

You missed a very important step.  Rinse the tank with a gallon or two of water mixed with a lb. box of baking soda.  No flash rust.

I agree on the por-15, it's a waste of money, red kote does fine for the inside.  That por 15 looks great on the outside though, great job. 8^)

The soda neutralizes the acid.

Edited February 21, 20178 yr by siteunseen

56 minutes ago, siteunseen said:

You missed a very important step.  Rinse the tank with a gallon or two of water mixed with a lb. box of baking soda.  No flash rust.

I agree on the por-15, it's a waste of money, red kote does fine for the inside.  That por 15 looks great on the outside though, great job. 8^)

The soda neutralizes the acid.

Good info. Thanks. I did my 78 with muratic acid and clean water. I didn't have the flash problem but on the 75 tank I need to do I will remember this.