Alyn Foundry CHUK 3 Mk 2

[RayW]

Thanks to Graham very kindly digging out his one and only set of castings for me, my latest Alyn Foundry project is now under way in the shape of the Mk 2 version of the horizontal CHUK 3 flame ignition engine. The Mk 2 version features a rotary flame inlet valve underneath the cylinder, operated by a pushrod driven from a cam inside the flywheel.
Progress to date consists of machining the base casting, cylinder yoke, cylinder and piston. The cylinder is fully bored and honed to a nominal bore of 40mm and the piston is a nice sliding, almost airtight fight. The flame admission slot and rotary valve hole in the cylinder are still to be tackled.
Photo 1 shows the castings as received and photo 2 shows the assembled components so far, with the piston just peeking out of the end of the cylinder. In practice, the piston would stop just short of the flame port slot when at TDC.

[Admiral_dk]

I see that you are of to a good start 

Per         

[Alyn Foundry]

A good start Ray. 

Four of the castings are genuine Rhuddlan foundry and were cast a 1/4 of a century ago. Sadly the gentleman that bought them became too frail to machine them and approached me a couple of years ago about building it for him. Strangely enough I was actually in the throes of building one at the time so I basically exchanged his castings for mine and finished the job.
Here’s a photo of the Mk 2 along side the other CHUK family members. And one of the improved cylinder heads.

   Graham.

[RayW]

Thanks Graham. Can you let me have details of the valve side of the cylinder head please.

[Alyn Foundry]

Just a photo available Ray.

The casting was made dual purpose for this one. It can be bored out to suit CHUK 1 ( old style ) or used with a central compression spring as CHUK V. For horizontal use note the little pin which stops the “ Chipmaster “ valve from dropping off the seating edge. Obviously placed at bottom…. 

I made the stub into a “ chucking stub “ first and then machined all the faces from that datum. The central hole was drilled to 3/8”  10 mm to accommodate a light compression spring. The exhaust holes can then be drilled to any division that suits your taste

   Graham.

[Jasonb]

That is basically the same as I drew for ChukV except that has 5 holes. The central pocket takes a weak spring and then the disc with the corners filed off that the other Chuks use fits inside.

An alternative is to have a round pocket to locate the round disc and then mill some passages for the gasses to pass when the valve opens, similar to Little Otto



Test piece, valve is 0.5mm thick

[RayW]

Thanks Graham and Jason but what does the valve disc close against? Is it just the end of the cylinder casting, or is there a plate between the head and the cylinder?

[Jasonb]

You should have a slightly raised lip around the end of the cylinder that can be lapped if needed

[Alyn Foundry]

Remember the raised lip you put on your CHUK 2 Ray? You can do the same on this one too. It makes lapping the face so much easier without the greater surface area.

   Graham.

  Jason beat me to it….

[RayW]

Damn, I didn't realise that and I have now finished machining both ends of the cylinder and honing the bore. It's going to be a bit of a pain to set it all up again now to remachine the head end. I need to be careful not to grip the open end too tight otherwise there is a risk of distorting the bore. Perhaps a plug fitted in the bore would avoid that. Some thinking is needed.

[Jasonb]

You could just have the valve sitting on the flat end of the cylinder, probably not that much harder to lap it is just a slightly larger surface.

[Alyn Foundry]

You could just have the valve sitting on the flat end of the cylinder, probably not that much harder to lap it is just a slightly larger surface.

I agree with Jason on this one Ray. Having the lip just makes the lapping many times easier than doing the whole surface but it will work just as well.

   Graham.

[RayW]

Thanks both of you for that. Will try that first.

[RayW]

I came up with a different solution to the valve seat problem caused by me forgetting to machine a lip on the end of the cylinder. Instead, I machined a thin brass ring with a raised lip against which the flap valve will seal. This ring is sandwiched between the cylinder and the cylinder head.
In order to make alignment of the cylinder head, ring and cylinder easier when drilling holes for the head bolts I have made the ring, spring, flap valve, and cylinder head into a single assembly by attaching the ring to the cylinder head with two tiny 6BA brass countersunk screws.
In the attached photos, the holes for the cylinder head mounting bolts are still to be drilled.
For those of you who are lovers of the wonderful strange noises made by the various CHUK engines, you will be pleased to know that this one is no exception. Holding the head assembly firmly against the end of the cylinder and pushing the piston briskly down the cylinder produces a wonderful farting noise!!

[Alyn Foundry]

And a very elegant solution it is Ray.   

Looking forward to seeing further progress….

   Graham.