Machining Cross Flow Cylinder Head for Piston Clearance

[1970S2]

Finally machined my cylinder head ( actually 2 of them ) My special hemi cutter tool used to make clearance into the head for the 10:5 pistons, each port was centered up and plunged down to make the correct clearance 2.0mm , I used soft solder taped to the piston, then revolved the crank to compress the solder, took measurement of solder and made the necessary adjustments to my depth of cut to achieve the correct clearance, this required taking the head out of the mill 2 times and re set it up , very happy with the outcome, I will now send the block out to hot tank it in order the clean out all the oil passages and remove any other gunk on the block, next I will lap the valves , the margins and seats are in excellent condition, and put the head together ..I will keep you posted of the progress

[TurboFource]

Nice work!

You centered on the port or the cylinder bore?

[1970S2]

centered to the cylinder , the head was installed  to the block  with all 4 cylinders and I scribed it to the head, without the crankshaft in place of corse, I indicated to the scribe lines. I'll post a picture later

[1970S2]

you can not rely to center to the head casting, I centered the cutter to the cylinder bore as shown in the picture, also the cutter is not a flat top, its contoured to the profile of the piston head

[Sandyman]

It was my pleasure to visit 1970S2 yesterday. I am in awe of the ability of a master machinist to think in 3 dimintions in spaces. Looking forward to seeing the finished Europa.
Sandy

[1970S2]

Nice of  you to drop in Sandy, looking forward to see your Europa !!

[MRN I J]

What is the piston to head clearance on the freshly machined part

[1970S2]

clearance is 2mm or .080 inches

[1970S2]

the piston clearance is with the head gasket on , I used the old crushed gasket to achieve the 2mm

[Richard48Y]

As long as you are at it, have you CC'ed the finished chambers?

[1970S2]

no, I have not cc the heads,

[Richard48Y]

Your pistons appear identical to what was in my engine.
They were Mahle brand.
What brand are yours?
Compression ratio and source?
All I can find readily available now are low compression cast factory type or Wossner.
Wossner forged are a good price but appear to have an odd bump in the crown and a bit too much compression.

[GavinT]

Hi Richard,

Generally speaking, there's two common categories of pistons used by we, the common folk.

The Wossner forged piston in your pic would appear to be of the 'BIG' compression variety usually indicated by that extra hump in the middle. Those are somewhere around 11.5:1 compression or higher and require relieving of the squish area for clearance and often referred to as the '160HP' kit. (pic below)

The cooking version used in road going OEM performance cars like the Euro R17-TS, R-12 Gordini and later Alpine A110 models was the 125HP version and doesn't have that extra hump in the middle of the piston and usually quoted as having 10.25 compression.

For example, here in Oz, Renault imported four R-12 Gordini to compete in the Oz rally championship. Those cars arrived with the 125HP engine installed and with the 160HP kit in the boot/trunk.

[Richard48Y]

My head has been modified to clear Mahle crowned pistons.
According to some sources no further modification should be needed for the Wossner pistons.
Leaning toward modified Wossner to bring compression down a bit to no more than 11-1.
10.5-1 would be my preference.
I also have an enquiry in to Wossner for custom pistons.