Hallo,
first of all many thanks again for your lively interest and the versatile and very nice replies.
In the mean time I could work a little further on the sleeve and cylinder garniture. As the ball mounting needs a little backing material to enhance the rigidity at the circumference I had turned a shoulder on the end of the sleeve which now has to be milled away, sparing only a small piece for the balls base and the coming soldering. This recess is also reducing the sleeves diameter from 20.00 to 19.80mm going up to additional 2mm above the ball mounting base, so this whole area does not take part on the sleeve to cylinder fitting and does not jam the outer lapping operations too.
Then came the similar pre lapping work like I did on the cylinder bore, I went to 0.005mm below the end measure so I don’t have to do too much grinding after milling the ports out.
For the outer diameter I had made a little lapping ring from aluminium and I’m holding the sleeve on a special fixture which will be needed for milling the ports anyway.
My port layout is a compromise of the small engine scale, my machining abilities without using CNC and a relative short sleeve stroke, depending on the desired shortened design of the whole cylinder elevation and the avoidance of too much expansion of the gear housing width.
Also I had to place the sleeve ports sufficient enough above the cylinder heads compression ring, otherwise I would get problems with the sealing during the combustion cycle, what in fact is limiting the port height too.
So I’m up to rectangular ports now without the tricky elliptical arches Bristol did on there engines. Free formed arches are a little bit difficult on a non CNC mill and filing them by hand was no real option for me.
But in comparison to the usual poppet valves my free port sections are not so bad. Each port makes 8sqmm free width at maximum overlapping position, that means 24sqmm for the inlet and 16sqmm for the exhaust. Calculating a high performance cylinder head (for the same cylinder bore) with two poppet valves at 30deg inclination to both sides of the spark plug the free valve sections will be approximately 20sqmm for each valve. Even a spherical head with four poppet valves would produce no more then 27sqmm per side and it would be a very tricky task to get four dimensional optimized and functional valves into a 18mm diameter head.
But cutting a long story short, now it was time for the fiddly milling operation, the first one was the sleeve…..
……and at last the cylinder.
And here we see the collection of the fixtures and lapping mandrels I have used.
This is the intermediate result of the port milling job.
Next thing to do was hard soldering the little (4.8mm) connecting ball to the sleeves base.
To enhance the joint I made a 2mm pin from ETG which is well fitted to both holes. Things went very well, the silver solder is filling up the gap sufficiently and was even travelling along the pin to the countersink at the inner side.
After the final lapping and fitting operations of sleeve and cylinder I could assemble the moving components for the first time.
Port locations and timing are fully according to my calculations and the sleeve motion is very smooth an easy going. I made a running test on my high speed spindle and had no problems to go up to more than 8thousand rpm over a longer period. So the present results are auspicious for the further progress of this little project.
Good night from Achim
