Today I spent quite a bit of time on working out the co-ordinates for drilling then reaming the holes in the cylinder block for the 8 valves and 4 cylinder liners. It’s critical that measurement should take place from a machined surface and I choose the right hand side face when looking at the photo of the cylinder block on the milling table. I had previously set the casting parallel to the X axis by using the two plugs centre drilled previously.

Setting the edge for distance on the Seal cylinder block casting

I normally use my electronic edge finder that lights to show contact, and therefore the edge (after allowance for ½ the diameter of the end) of the part being measured. However the overhang on the edge finder would not allow measurement and I do no possess any slip gauges or the like so I made use of the ‘wiggler’ set I used before buying the electronic edge finder.  It was quite nice to revisit an old friend as it were and the edge was fed into the digital readout, after allowance for the ½ diameter.

Because the cylinder block is a substantial casting and the critical nature of making sure the valves, cylinders, camshaft etc. line up, I made several movements to see that the end co-ordinates looked correct. It was during this exercise that I found the co-ordinates wouldn’t work in relation to the 4 holes already there for the pistons.

Due to the oversize casting the co-ordinates had to be 'adjusted' to bring it right.

(above is supposed to be the centre of the 4th bore!)

When checking the dimensions against the other recently bought set of castings, I found yet again that my casting was significantly larger. So I decided to center the mill over the nearest cylinder hole to the datum face and confirmed the ‘extra’ distance. So after recording the measured difference in case it is needed later, I reset the DRO to zero and carried out the checks for the co-ordinates again. This time everything worked out fine and I decided to center drill the 8 valve stem holes. Then it was the turn of a 15/64” drill before reaming with a ¼” reamer.

Ignore the surface finish, theres 50 thou yet to come off

The remainder of the session was spent adjusting the belts of the milling machine to reduce speed for boring and a start made on the first cylinder bore. However at the beginning of the next session I will make a plug of the correct size to use as a set standard for all four bores. Whilst each cylinder liner can be ‘adjusted’ to suit I would like to get them as near as possible to the correct size so I can produce the 8 cylinder liners as a batch. After all I should seek to increase my engineering skills, and accuracy is a measure of progress is it not.

Overall a good session with the many checks proving of worth, even if there was not a great deal of swarf made!