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spuddevans:
A little update on this.

I discovered what is almost certainly the cause of the escaping air. In efforts to trace any problems I took the top section and hooked up air to one inlet at a time. I found that one piston valve leaked more than the other, but both piston valves leaked. I dismantled one of the valves and measured the "piston" part of the valve, and it was 5.82mm. The bore was reamed to 6mm.

No wonder there was a lot of air escaping.

When I made the piston valves originally I made them out of some 6mm stainless rod, or so I thought. I measured the piece of 6mm rod I used and found it to be 5.9mm.

So this afternoon I remade one piston valve from 8mm steel and turned it down to fit snugly in the bore. After re-assembling the valve assembly to the cylinder and the whole top section to the bottom section, I then hooked up the air to just the newly made valve and turned on the compressor.

Virtually no leaking air and the engine tried to turn over. There is still some binding in the conrod/crankshaft area that prevents the engine from spinning freely. I think that I'll have to shave a little off a boss on the crankshaft bearing blocks to give a little extra clearance, and I have to remake the other piston valve too.

Tim

sbwhart:
Hi Tim

Your at the stage where you really start to learn about your engine, what's needed now is a nice methodical approach to tease out the problems, as you have been, and you'll soon get a runner for sure.

Keep at it

Stew

spuddevans:
Thanks Stew, aint that the truth. When I started to assemble all the bits together, I had to go back over the plans in order to find out what went where, it had been so long since I started it I had forgotten :doh:

Now that I've had it apart a couple of times, and back together too, I am getting to know it a bit better.

At first I was going to go at it with all guns blazing, kinda like "right, lets re-make everything at one time and then try again" sorta attitude. But then calmness and reason set in and I realised the truth of what you said, work at the problem methodically. So I removed the part that I thought was the issue ( the reversing/speed control valve ) and applied air direct to one piston valve/cylinder at a time, and that was where I found the one of the problems with the escaping air.

So now I can re-make the other piston valve ( which, by the way, leaked worse than the one I just remade ) and sort out the binding con-rods and then try running it again.

So, step by step it is, I am learning that with these little engines, it only takes parts to be a fraction off the size that they need to be in order for things to either bind up or be too loose a fit. All part of the learning process.

Tim

kvom:
This was tricky for me to get running as yoyu probably remember. The main problems I had were (in no particular order)

1) Binding in the crankshaft parts. I disassembled the bottom completely and lined up the bearing blocks with a length of drill rod, then tightened down gently so that the rod would still turn fairly freely. Then I could assemble the crank components again.

2) Binding in the guides. I basically got it running with only one guide rod per cylinder.

3) Getting the timing precisely right.

spuddevans:
Yea, I remember you had some issues Kvom. So far the guides are fairly smooth and free, (oops, shouldnt have said that, they'll probably be stuck tight when I get back into the workshop )

On mine the crankwebs are binding with the con-rods once each rotation. They are only slightly binding, so I think I will just shave off a few 0.01mm's from the bearing blocks to allow the webs to be widened by a tad.

Tim

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