I've been working on this project without posting anything, probably because I didn't have anything positive to post. But that's silly, you can't always post the good stuff. So here's the present state of this conversion.
I received the timing pulleys and belt and made up the valve spindle. I replaced the old piston rings with new ones, lightly honed the cylinder bore, replaced all gaskets and shaft seals with new ones, replaced the old head bolts with shorter Grade 5 bolts to suit the new head height. I blocked off the old poppet valve recesses in the head, and assembled the head and mounted it on the engine. I also mounted the old flywheel.
I gave the engine a try on compressed air, from 10 psi up to 100 psi pressure in steps. It wasn't a runner. The cylinder would move to BDC and stop. It was obvious that there was leakage between the inlet and exhaust ports.
I discovered that there was porosity in the casting along the valve spindle. This would mean scrapping the head and re-casting, as there wasn't enough metal to put a sleeve in.
After thinking about it for a short time, I decided to try using a sealant in the spindle bore as a temporary measure for running on compressed air, just to get the engine moving. So I swabbed out the interior with high-temp metal filled epoxy, let it cure and drilled and reamed again. I knew this wasn't likely to work for long, if at all, but though it was worth a try before scrapping the head. I can't pour metal now because of the winter build-up of snow and ice outdoors where my foundry is. So a new head will have to wait.
The sealed head was definitely better, but the leakage problem was still clearly audible. It may be that the swabbing and filling was incomplete. The engine did reactmore quickly, but still stopped just past BDC. I did try adjustments to the timing by altering the timing pulley positions, but never got past rotation to BDC.
The inlet and exhaust ports through the head into the cylinder are not joined on my design, and I thought that some of the leakage might be traveling axially on the valve spindle. So I added four O-rings to the valve to seal the valve areas from each other. This made a big difference in the amount of leakage. But still the engine could not get much past BDC. The rotation was much more lively, but not enough carry through. I don't think I can get any better without making a new head and valve assembly.
Probable and possible issues:
1.) remaining porosity and rough bore
2.) oversized bore
3.) cold temperatures increasing the clearance of aluminum housing and steel valve (testing in winter with compressed air vs live steam)
4.) flywheel too small
5.) lack of run-in time, high engine internal friction.
6.) valve timing -- cutoff too short (inlet @ 10 BTDC, cutoff @ 90deg ATDC) - more appropriate for steam running than compressed air on this engine
7.) cross port leakage is still present -- audible inlet flow even after BDC if the crank is held stationary. I don't know if this is flow into the cylinder or along the valve. Probably the former, now that O-rings are installed
Anyway, there it is. I'm not giving up. But I definitely need a new cylinder head and valve design. I'd still like to do it with a rotary valve, but the first attempt was pretty much a stab in the dark.
Here's the engine assembled.
