Cooper S cylinder head thickness

[Minicooper1964]

What is the std head thickness- mine measures 2.730

[whistler]

I believe it's 2.75"

[Exminiman]

Can anyone help out with realistic, minimum head thickness on 12g940, its going on a 1310CC engine.

Currently have got apx 2.722”......be interested on any opinions before go to the effort of working out the CCs

Thanks

[winabbey]

I believe it's 2.75"

Confirming your belief, the engineering drawing for the 12G294 head shows the thickness to be 2.718 to 2.75 inches.

12G294 Cylinder Head Complete Subset Thickness.jpg

[Exminiman]

Thanks for that, looks like someones shaved about 50 thou of the face, not sure if thats too much or not, looks like will have to measure the CCs…

[Spider]

I believe it's 2.75"

Confirming your belief, the engineering drawing for the 12G294 head shows the thickness to be 2.718 to 2.75 inches.

That's a huge difference between these numbers, much more than a manufacturing tolerance. Doug, I see there's a note attached to those figure, no. 5. What does that say ?

[winabbey]

That's a huge difference between these numbers, much more than a manufacturing tolerance. Doug, I see there's a note attached to those figure, no. 5. What does that say ?

You'd know more than I how the difference translates into practical application - 0.032 inches or 0.8 mm. Is that a lot?

The change number 5 relates to the use of actual dimension limits versus the previous plus and minus variation. The figures are a little difficult to read, but appears to be 2 47/64" plus or minus (unreadable) 64ths.

12G294 Cylinder Head Complete Subset Thickness 2.jpg

Out of interest and shown on the drawing is this reference to combustion chamber volume.

12G294 Cylinder Head Complete subset chamber.jpg

[iain1967s]

The figures are a little difficult to read, but appears to be 2 47/64" plus or minus (unreadable) 64ths.

The (unreadable) would be:

2 47/64” with tolerance of plus zero, minus 1/64”
i.e. 2.734” to 2.718”

Looks like they basically opened the tolerance up to be plus or minus 1/64” of the 2 47/64” nominal.
i.e. 2.750” to 2.718”

That makes it easier for manufacturing. Machinists hate working to zero toleranced dimensions.

An overall ~32 thou variation isn’t that big a deal, since they are just accumulated tolerances across the full thickness of the head. In fact I’ve got a head that varies by almost that much from one end to the other

The chamber volume, guide heights etc. are all referenced from the front face, and other than spring and pillar base height there isn’t anything that is dimensionally sensitive on the rocker side of the head, as it can be adjusted easily via the rocker arm screws.

[Spider]

That's a huge difference between these numbers, much more than a manufacturing tolerance. Doug, I see there's a note attached to those figure, no. 5. What does that say ?

You'd know more than I how the difference translates into practical application - 0.032 inches or 0.8 mm. Is that a lot?

The change number 5 relates to the use of actual dimension limits versus the previous plus and minus variation. The figures are a little difficult to read, but appears to be 2 47/64" plus or minus (unreadable) 64ths.


12G294 Cylinder Head Complete Subset Thickness 2.jpg


Out of interest and shown on the drawing is this reference to combustion chamber volume.


12G294 Cylinder Head Complete subset chamber.jpg

Thanks Doug. For a Deck Face, a difference of 0.032' is a lot. For comparison, on a typical head recondition deck 'clean up' I would usually only take maybe as much as 0.001" off. In several of the Factory Special Tuning Manuals, for the 1275 heads, they quote a figure of 0.012" 'approximately' equalling 1 cc of chamber volume. ) 0.032" is a variation here of 2.66 cc.

Interesting extra detail on the Chamber Volume too.

[mk1]

Better copy of note 5

tol.jpg

[Exminiman]

This is the spec for a brand spanking new head, so is the minimum dim, the 2.718 thou, the minimum "new" manufactured thickness - assuming you then can also achieve the 28.29 CC chamber size as well ?

EDIT, re read this , am I just stating the bleeding obvious