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L series head thickness variation. Why?

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Searched, but couldn't find anything. I have a U67 head that measures 4.255" that I suspect is an uncut head. My race head measures 4.238", it's supposed to have had .030" cut off of it.


The Datsun Bible states 4.218" stock thickness of L heads. What gives? Anyone else run into this?

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Yes, I have run into this. My machinist says virgin thickness is 4.260" according to all of his old sources. He used to build L-Series race motors. This is, however, not what most people quote as the virgin thickness of heads, which is 4.248". I am not sure what the deal is. I put calipers to one of my heads that had been resurfaced, and the measurement was 4.252". I found someone else on the internet that found the same thing.


I don't really care to start an arguement about this--as there was one started before--but personally I think the some of these numbers that are passed around may be nominal thickness. Possibly there are some variations or maybe the information is incomplete. All I know is that I have come across this, and so have others.

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Just like machinery ...

not all measuring equipment is the created equal.

Nore is any two person's measuring technique (literally lol)


Kinda what I was thinking.


Why with taper measures, I never start at 0, but at least at 1", I mean what part of the tape measure is actually 0"? Is it tape side of the hook? or non tape side? Or the plane that the hook lives in (abstractly)?

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Lol, oh you guys. I'm not measuring this with a tape measure. :D Measured several points with my calipers. Definitely not bad measurements, I actually do know how to use my calipers. I'm just curious why there is this discrepancy. The head I measured was from the motor built back in the 90s, when U67 Datsun heads were probably a dime a dozen. I almost wonder if there was a difference in the Japan motor heads vs. the american market heads, and with the prevalence of imported motors back in the day, perhaps that's what we run into? I'm going to go measure the L16 head I have.

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I do agree. The exception is there is different aspects on this.


On "some" tape measures ( of many ) manufacturers the hooks are @ "0"

Others are indeed not exactlt right there

Over time bending/prying/pushing of the hook and or the size/looseness of the rivets for the mark "0"


Does not allow for an exact quality control/setup across many manufacturers


^^^ combine this with how people measure and their true "zero" is what laecaon was reffering to.

I know @ age 16-17 doing framing work my tape measurers were beat and never the same lol.


The act of letting the tape measurer "snap back" ruins them too.

Even wheb the darn things kink it starts to screw them up lol.


With the exception of machinist rulers ... ( grandfather was a machinist )


Go to home depot and grab 5-6 different tape measurers ... measure what laecaon was talking about



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4.258" original L16 210 head. I think the numbers are just plain wrong unless they're measuring from some weird ass diameter. I measured that through the timing cover opening, against the cam tower bolt boss and the corresponding point on the edge of the combustion chamber. No way to f that up, not by 40 thousandths.

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I use a tape measure sometimes hundreds of times a day, and I'm not a carpenter. I go through 8 or 10 a year but mostly from loosing them. Yes they do wear out but mine usually get so rusty from scratching the ground that you can't read them and accuracy is important. A carpenter's tape measure is useless for measuring a head, accurately at least.

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Well ... all I know is between myself/friends/family ... that work with their hands ... there is quite a few factors


Im def not saying anyone is wrong or did it wrong.


But a great example is ratsun = people ask how to measure all kinds of shit all the time. Some know ... some don't ... some guesstimate last micro of measurement ... some break out a 20-laser emitting self leveler


Heads can be milled badly ... warped badly ... etc ... giving flase readings too ( as everyone knows)


I'm just thinking there is more to the process than what should be a simple measurement



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Guest 510kamikazifreak

Not what I said or meant . I was aiming at the " thinking " not implying measuring a head with a tape measurer or even attempting to ... :lol:





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The heads were milled top and bottom at the factory, so there's going to be variation. Could be +/- .010 from the factory.

I'm assuming that this is also the reason some camshafts came from the factory set to different cam timing locations, as I've heard of some cams being set at #1 from the factory and others set at #2 from the factory.
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Everything made has some tolerances. If there were not some tolerance, it would be prohibitively to make anything. The trick ti to allow a greater tolerance in non critical ares, and tighter tolerances, where it is important.

On a cylinder head, the important tolerance is the combustion chamber volume, and the distance from the camshaft to the valve stems, (OHC engines) Not so important is the height of the surface the valve cover bolts to.

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when I left school I worked in a factory which manufactured deep sea drilling pipes for offshore oil rigs. Measuring the same pipe with a micrometer on a hot day versus a cool day taught me one way tolerances can vary

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