Hi David,
Back in the metal work fold now! Sally and I are keeping well away from people - just one weekly trip to the supermarket and a daily walk down to the sea or round the marsh so plenty of time in the workshop.
Still some work to do on the bore of the cylinder. I took the large scratch marks out with a 3 stone hone but I think the bore needs to be a bit smoother for an elastomer O ring. The aluminium lap seems to be wearing away much quicker than the c.i. so I may have to investigate something more sophisticated.
Now that the bore is (pretty much) to size I've started on the cylinder head - turned in the lathe with the locating spigot fitted to the bore. I kept a small centre mark from the lathe to locate in the milling machine.
I used the DRO to locate and spotted the holes for the studs to fasten the head to the cylinder and removed the head from the mill to the pillar drill for the 4BA clearance holes (no quill on my mill) then returned the head to the mill using two clearance size drills to relocate the head in the vice
I spotted the 2 holes for the valve guides and milled the pocket for the spark plug with a ball nose end mill. I'm using close(ish) metric and BA equivalents to the original drawings.
The head was returned to the 4 jaw in the lathe and I picked up the cenrtres for the valve guides with a wobbler
and then drilled, bored and reamed to size
I decided to make a jig for the next step which was to drill the spark plug hole at a 20 degree angle. Easy to do as I already had the coordinates for the stud holes
Then tapped 4BA
The jig was set up in the vice at 20 degrees. Jason will be amazed that I'm using my special aluminium magnet again! The angle gauge has a V slot on the base so in order to get it to sit on the cylinder head between the bolt heads I used a round steel bar and there was enough magnetic flux to stick the bar against the hold down bolts.
The spark plug sits in a pocket that should be 7/16" diameter. I have to be careful here because anything bigger risks breaking into the holes for the valve guides. The only 7/16" milling cutter I have is this rather old fashioned 6 flute one and I didn't fancy my chances of starting a clean hole with this so I used a 12mm 2 flute mill to start and then finished off with the old cutter
The drawing gives the dimensions to get the hole in the right place...
...but it was still a relief to find that the result was near enough in the correct location. I tapped the hole for the plug and it seems to fit
I didn't plan that job terribly well. I changed my mind several times about how I was going to do it so ended with several redundant transfers from machine to machine but got there in the end.
Stay well everyone,
Rod
Oops. Seem to be having a problem with the pictures. I'll try and sort it out tomorrow
Update: Was using Flickr to host but that didn't seem to want to play so now trying Ondrive - I think I've got it sorted