Down but hopefully not out for long Alan!

The original idea on the pistons was to have custom ones made, because none of the off the shelf XU ones are an exact fit for the XU7J4. Knowing what I know now, I could have saved alot of time and hassle! I had some Omega Mi16 pistons back along, which I measured, but the top ring land was too close to the crown to allow the crown height (height from pin centre to crown edge) to be reduced (I need 2.7mm less crown height than the Mi16). I set about finding out the other day if there's enough material in the standard Mi16 crown to allow enough machining.
First off I drilled some holes in a scrap Mi piston to establish the material thickness in the crowned:


Then turned off the required reduction in crown height around the circumference of the piston, to make the centre into an intruder. Next step was the biggie! After a great deal of time spent setting up Colin's Bridgeport mill (including Colin making an arbor for the cutter with typical casual ease), I could set about deepening the valve cut outs to suit the revised crown height. This entailed establishing the valve guide angles and the exact position the valve centres strike through the head face plane, so that could be replicated anmarked on the piston, to centre the mill head for cutting. After all that I was able to deepen the cutouts simply by winding the mill bed up by the desired amount. I actually broke through to the ring land on one by over cutting it to see how much material there is. After that I restored the mill head to 90 degrees to cut the squish area down to the correct height. Here's the result:


This would have been a practical solution for this engine, Mark Shillaber built an 8v 1.8 XU using the same method on the pistons,which has been used competitively with an 8500rpm limit for several years. However the discovery of some new JE pistons that I can convert similarly is even better really!