Wanted to complete all machining of main casting before Christmas as we were to have family stopping over.
I set my angle plate up on table and checked face was at 90 degrees to X axis and the face was vertical. It took a long time to work out how to fix the jig plate to the angle plate. In the end I had a thick parallel resting on table bed and two small 1-2-3 blocks on top of this. The edge of the jig plate rested on the two 1-2-3 blocks. Was then able to use clamps on the top edge of the jig plate onto the angle plate. Tapped down onto the 1-2-3 blocks and then could insert threaded rods in the gaps under the jig plate and through the slots in the angle plate. I just had room to clamp the lower edge with standard table clamps. It was solid.
Zeroed the DRO X-axis on the line between the jig plate and main casting and the Y-axis on the cylinder head face. Moved to what should be the bearing centre on the split line. Fitted laser centre and checked I was on the correct location. Perfectly aligned.
Whilst laser was still fitted did a sanity check on 1.25” bar fitted in the bore.
This was parallel to Y-axis. Note in this picture the lower clamps can be seen. As a further check I fitted the optical centre and this picked up the bearing joint line perfectly. Now happy to start boring out the bearings.
Spot drilled the centre and then worked up from ¼” drill to 3/8”.
At this point fitted long centre drill and spotted the middle of lower bearing. I drilled the upper bore at one size and then drilled the lower bore at the size below until had both bores up to 19/32”.
Prior to this I had spent some time at my mates house where we did some trial bores on a piece of cast iron to see which was best boring head/bar combination and whether or not to ream to final size. On testing my 5/8” reamer it cut 4 thou oversize, so that went out of the window. I have two boring/facing heads but had no boring bars small enough for either of them, an Arrand boring bar but the bar for this was bit too flexible. I ended up using the ubiquitous 50mm boring head sold by all the usual suppliers. I used the short carbide tipped bar for the upper bore.
On the top bore I went up in size very slowly and the last few thou had about 6 passes at each setting. Had clean piece of paper under the hole so I could see the material being removed. The Oilite bushes were nominally .625” but they were actually .6261.” I managed to get to dead size and with a firm push from my thumb the bearing went in the hole.
Extremely happy, just needed to repeat on the lower bearing.
I changed to the longer bar for the lower bore, but did not fully push it fully home. I just had enough length for the tip to finish cutting and partially exit the bore and still leave about 1/8" clearance between the boring head and casting. The auto stop on the down feed worked very well.
longer bar was a little more flexible and I was doing 6 to 8 passes for each size adjustment. Eventually second bearing also pushed in.
With the bores done, moved onto the reamed hole for the timing gear. This went okay. When I came to the slot for the push rod, the boss on the casting did not appear to be quite where it should have been and the tapped screw holes would have been right on the edge of the casting. I elected to put them in the centre of the casting which put them out of place by 110thou. Looking at the length of the latch-out bar I do no think I will have a problem. Lets hope this is not “famous last words”.
I also drilled and tapped for the spark plug. This is exactly as per dimensions on drawings, but the boss on the casting is a tad high.
I then removed the casting from the jig plate and turned it over and remounted it, located and then drilled/tapped the 1/16” x 27 NPT hole for the fuel outlet union. Removed from jig plate, did some fettling of the casting around the bearing , and then assembled the bits so far.
The engine castings, as said before, had been started and I had been given a fabricated crankshaft. When fitted in the bearings and all done up, I could turn it but not very easily.
Did I have a problem with my boring or was it the crank. Only one way to find out, remove the crank and replace it with a ½” diameter length of straight bar.
This turned nicely. I will have an attempt to see if crank will straighten, otherwise will have to make a new one.