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I’ve always seen the same color on the grill no matter where I look so I assume the grills were painted everywhere in the same gray. Never seen any hint of old plating on those long bolts.

As I mentioned yesterday, the problem appears to be only with the exhaust valves. So, it is with interest that I made the following observation for valves 5 and 6 (with 1 to 12 being from the front of the engine to the back). These rockers are both actuating exhaust valves and are "adjusted to correct valve lash". Note the very different adjuster heights between the two: Wild - right? Well... have a look at this picture - the rocker on the left is the number 6 valve (exhaust) and the one on the right is the number 7 valve (intake): So... what is going on with the rocker on the valve on the left? Do you see how the tip of that rocker appears to be "floating"? And compared to the intake valve on the right, the rocker tip on the left appears to be sitting quite a bit higher (above the retainer) actually: Here is a picture showing the underside of the rocker - see the shiny part where the arm was contacting the retainer? Summarizing what I have found tonight, each of the 6 exhaust valves are hitting the top edge of the Isky retainers. When I was setting valve lash, I was setting it with the rocker arm sitting on the retainer instead of the lash pad. The rocker was floating above the stock .118" thick lash pads on each exhaust valve. During the total of about 1 to 2 minutes of engine operation at low revs, the cam was operating the exhaust valves, initially by rocker to retainer contact, but as the rotation continued, the rocker tip came into contact with the stock lash pad, and operated the valve. And note that the lash pads look very different. The ears on the lash pad of the intake valve (right) are sitting quite a bit further outside the retainer. I removed that rocker and took a measurement of the lash pad: Each gradient is .025". So the reading above is .177" and 7 tenths, or '.175'. These are the lash pads that came with the cam when I ordered it. I am hoping to get lucky here. My plan at this point is to put the .175 lash pads in each of the 6 exhaust valve locations and to modify the undersides of the rocker arms for clearance with the aftermarket Isky retainers. I'll just have to see if between the two, the rocker arms actually sit lower at the tip than before. If so, then I should be able to raise the height of the adjusters for these valves. Fingers crossed.

While it is true that the tip of the valve is going to be in the same location... and the lash pad will sit on top of that in the same location, the location of the upper spring perch is different between the stock and the Isky retainers. Therefore, just swapping out the retainer to a stock one is going to to change the location of the upper spring perch and the installed pressure of the springs. It may be possible to remove or add shims. I will have to investigate more closely. Here is a link and brief description of the retainers I bought. Chrome moly valve spring retainer set "Made in the USA by Isky cams. These will fit Datsun L series engines found in the 240Z, 260Z and 280Z. High quality parts made for racing or street use. Includes 12 retainers. These retainers will alter the installed height, for use with Isky high pressure springs PT# 800-1374."

No

There are 2 positions where the motor is at TDC in a cycle! You need the position where the two cam lobes on the first cylinder are pointing upwards and not pushing on the valves. The timing pointer on the crankshaft pulley should be pointing to the first mark on the the pulley. With all the spark plugs out you should be able to rotate the engine with a ratchet. You can verify the piston is all the way up by looking in the spark plug hole or using a screwdriver to feel the top of the piston. The dizzy should be pointing at the #1 spark plug in the dizzy cap. Remove the dizzy and replace with the new one...

I do not know offhand if the Isky retainers and the stock retainers are the same on the underside. They might be. I think that swapping to the stock retainers will alter the installed heights because the keepers lock in a different location relative to the spring seats. I will explore the possibility of using them this weekend when I pull off the Isky retainers.

Don't get me wrong. I'm not trying to throw the engine builder under the bus. I'm just trying to make sure I understood what happened. Mistakes happen. So, why don't you just use stock spring retainers? Is there something different about the tops of the Isky springs that makes them incompatible with the stock retainers? Or is there something way better about the Isky retainers that make them a better choice over stock? It's not like people are complaining all over the internets that the stock retainers are inferior. I've never heard of a failure. Ever. Or you're thinking that since you paid for them, dad-gummit, you're gonna use em!! I mean if that's it, I get it! Haha!!

Ok, it seems the exhaust valves have been "sunk" deeper than is "typically done". And, it is likely I now have a situation where installing the .175" lash pads which were recommended by Isky is not going to work like it would as designed/intended. So, what I am very likely about to do here (machine the retainers) is not "normal". I get it: going far astray from what is usual may not be wise. The Isky retainers can be used with a broad range of cam regrinds, but the one I am using in this engine is very mild when considering the spectrum of available options. Modifying the retainers to use these thinner lash pads in this instance doesn't seem all that radical to me.

"If the engine machinist picked the lash pads and declared the wipe pattern "correct", then he must have overlooked a real problem!" - I think that is accurate. I am willing to forgive this mistake. I've got incredible amounts of value from talking with him over the years, and he has done a lot of great work also. I think I consider myself fortunate that no significant damage was done, and we'll get it sorted out pretty quickly.

It has been a few months since I have updated, but been very active working on the car. The original gas tank was saved, cleaned, and installed back onto the car. I am no longer having to change fuel filters every tank of gas. I upgraded the stereo from the 1980s/1990s pioneer radio dad installed to a retro sound unit with new speakers installed in the back and under the dash with mounts from motorsport auto. Ive attended a few carshows, and the car is running strong. Side note, my son bought back my old 300zx from the guy I sold it to.

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