L series head thickness variation. Why?

[DanielC]

Years ago, while I ws still in high school, I was awarded a grant to attend the GM training center, that used to be in Tigard, Oregon. It is the building across 99W, from the exit off 217, going north.

If my memory serves me right, I believe when we were talking about piston to bore fit, they mentioned that actually had four different sizes of pistons classified as standard bore, and that were lettered A, B, C, D. The differences between the four sizes was a few ten thousands of an inch. The bores were measured, again down to a ten thousands of an inch, and no, this was not done by some guy with a telescoping gauge and a micrometer, or even a dedicated bore gauge. I forgot those details, but after the bores were measured each cylinder was stamped with a letter, A, B, C, D. When the piston were matched to the cylinder bores, "A" bores got "A" pistons, and so on.

[ggzilla]

That's called "select fit" and is a form of blueprinting. Nissan does that too for some engines. It is not necessary but is done for special cases where they want to improve quality or meet advertising statements. So it goes in the factory service manual.

 

 

For example SR20DE has STD1 through STD6 main bearings.

 

 

Or STD 1, 2, 3 or 4 main bearings for Nissan QG18DE engine:

 

[Z chopper]

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

 

:)

 

 

uhmmm talking about measureing heads and you start talking about working with hands, :rofl: working with hands is what may be causing warp and false readings

[HRH]

Get your head out of the gutter Stiffler! :D

 

And yes, combustion chamber volume it the important thing. It's just odd that there is as much as .040" variation in the "factory" head measurement.

[I'm BLUE]

 

 

 

uhmmm talking about measureing heads and you start talking about working with hands, :rofl: working with hands is what may be causing warp and false readings

 

:lol: weirdo ... haha ! Ohhhh boy zchopper ... freud would have a coke day with that intrepretation ^^^ :lol: (dry humor)

 

HRH good topic ! I've seen it discussed a bunch before just not that much thought. Curious !

[datzenmike]

And yes, combustion chamber volume it the important thing. It's just odd that there is as much as .040" variation in the "factory" head measurement.

 

The head to block surface might be set and it's the valve cover surface that varies up and down.

[HRH]

But that can't be either Mike. The valve cover surface is dead even with where the cam towers bolt to the head. (Not that a cam gear up or down .040" would make much difference I suppose.)

[HRH]

Haha! I have information! I'm up at Sunwest right now and had Mike print me out the specs according to his machinist guide. This is Sunwest Automotive Engines.

 

New thickness for a '76 Datsun u67 head is 4.260

minimum thickness is 4.245

 

A '72 240z has a new thickness of 4.248

Minimum thickness of 4.235

 

A '78 280z is new thickness of 4.252

Minimum thickness of 4.232

 

Cleaned this up a little, was posting from the phone earlier.

[brodster]

Haha! I have information! I'm up at Sunwest right now and had Mike print me out the specs according to his machinist guide. This is Sunwest Automotive Engines.

 

New thickness for a '76 Datsun u67 head is 4.260

minimum thickness is 4.245

 

A '72 240z has a new thickness of 4.248

Minimum thickness of 4.235

 

A '78 280z is new thickness of 4.252

Minimum thickness of 4.232

 

Cleaned this up a little, was posting from the phone earlier.

 

Good find.

 

I wish it was about 10-20 years ago when there were more uncut L-heads, but it would be interesting to start collecting data on head thickness. We would have to standardize things an ensure people were actually using a micrometer or at least a good set of calipers, but it would be interesting to compile empirical data on this subject.

 

I do have one question though: Are there any other heads and years listed?

[HRH]

Couldn't find much more information. Most head shops just check the overall and most people only want a cleanup pass of .005" or less, in which case it really doesn't matter much for compression. We did check a 72 510, but it kept listing it as a Sentra in 72 with an L16 and not giving and numbers, so figured the database sucks for 210 heads. Tried '74 truck with L18 too, no information listed for '74 in trucks. If I bother to cc the chamber, I can probably get a pretty good idea, but that's assuming the cc measurements in the Datsun bible are correct, as the head thickness is definitely not.