TZR250 3MA
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Because I gona lift the cylinder need to compensate that amount at the top.
Therefore I changed the head, took max what i could and that's about 0,5mm
All my spare heads where damaged so I cleaned them up first

Head looks resemble at the first look

But after its first clean, seems it needs more work

So cleaned the whole head until it had hardly any pitting

It starts to look better

Last part is machining the O-ring grove

And there she is

My changed heads
1) Oem head only a O-ring.
2) Changed head with rounding in combustion shape.
3) Changed head with tight combustion shape.

Tight combustion shape and a wide squish band

Rounded combustion shape and a normal squish band

Oem combustion shape and normal squish band

Head volume checking

1) Oem head 12,2cc
2) Changed head 10,5cc
3) Changed head opened bowl 9,9cc

Changed head measured 10,5cc

The head with the wide band and small combustion shape hade 9,9cc
I opened the bowl a little bid to smaller the band and enlarge the combustion shape

Changed head (opened bowl) measured now 10,9cc

Did some measurements to find some base line.

Found the following

1,0mm base gasket gives 0,9mm squish and a total volume off 9,5cc
1,5mm base gasket gives 1,3mm squish and a total volume off 10,7cc

1,5mm base gasket with stock head gives 13,5cc

Leveled the engine horizontal, and measurer the total head volume

Head wet after the measurement, you see a little bid grease to seal off

To get a 12,5cc combustion volume I needed to open the bowl a lot.
This mend that the squish band was getting narrower, hope it will work OK

Have changed the head volume.
12,3cc with a squish of 1,3mm

Special head, combustion chamber inside the cylinder
12,4cc and a squish from 0,9mm

Inside the cylinder

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