Author Topic: Alyn Foundry Sphinx  (Read 5492 times)

Online Jasonb

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Re: Alyn Foundry Sphinx
« Reply #75 on: July 24, 2019, 04:50:42 PM »
Have you made the balance weights bigger to compensate for all that extra weight of the solid extension compared with the hollow piston shown on the drawings?

May have been better to have a larger diameter spigot say 33mm and hollowed out the extension to 3mm wall and crown.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #76 on: July 24, 2019, 05:13:52 PM »
No, I have made the cranks webs exactly as per drawing. I figured that with such a heavy flywheel, the extra weight of the piston wouldn't be a problem.
Ray

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #77 on: July 26, 2019, 12:40:55 PM »
After pondering further on Jason's comments about the piston weight, I managed to dismantle the two parts by chipping away the JB Weld from around the screw head, then applying heat with a gas torch to soften the thin film between the two parts.
Once they were separated, I hollowed out as much as possible from the extension piece before re-assembling. I also used thread locking compound on the screw rather than JB Weld around the head.
I propose using three Viton O rings as piston rings as they have proved excellent on other engines that I have built. I have just ordered them and will delay cutting the ring grooves in the piston until they arrive.
Ray

Online Jasonb

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Re: Alyn Foundry Sphinx
« Reply #78 on: July 26, 2019, 12:56:42 PM »
The Vitron does seem to work well, you may be able to leave a groove or two empty as I only fitted one to the Allman and did not put the iron rings into the other two grooves, less drag too.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #79 on: July 28, 2019, 03:57:47 PM »
More progress yesterday and today with completion of the crankshaft. Just needs a final polish up, but I will leave that until I am ready to assemble the engine.
The joints are all silver soldered and pinned with 5mm steel pins Loctited in position. The completed crankshaft is quite a solid lump, weighing in at just on 0.9kg, and it took a surprising amount of heating with the propane torch to reach soldering temperature.
Next job will be to complete the connecting rod which needs the little end block and bush added. The piston also needs turning to size and the ring grooves added, once the O rings that I ordered have been received.

P.S.  OK, did anyone spot my deliberate mistake? Since typing this post saying that the crank was finished,I have just realised that it is lacking two vital things - the keyways! Another job for tomorrow.
« Last Edit: July 28, 2019, 04:40:23 PM by RayW »
Ray

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #80 on: August 03, 2019, 04:42:20 PM »
Been working on the eccentric mechanism for the exhaust valve today and pleased to say, Graham, that my concerns about the undersize casting for the eccentric strap were unfounded as I managed to bore out to the necessary size without a problem. I also reduced the diameter of the outside flanges to 1.75" to match the OD of the casting. The ring that is left may be a bit thinner than the drawing, but should be plenty strong enough. I still have to make and fit the pushrod which operates the star wheel and opens the exhaust valve.
As can be seen from the photos, the exhaust valve and extension guide tube are currently quite a bit too long, but I will leave adjusting them until I have made the pushrod assembly, then I can see exactly how much to shorten them by.

I am hopeful that the engine will have excellent compression once everything is tightened up and sealed. To test the fit of the piston in the cylinder, I held the cylinder vertically with the bottom sealed against a sheet of rubber, then put the piston in to see how far it would drop. The answer was hardly at all. In fact, if you tried to force the piston down it would actually bounce, so it appears there is no significant leakage past it. As soon as the bottom seal was broken, the piston  immediately dropped to the bottom. If it is that good now, it should be even better with one or two Viton o-rings as piston rings.
« Last Edit: August 03, 2019, 08:40:40 PM by RayW »
Ray

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #81 on: August 06, 2019, 08:03:06 PM »
Hi Ray.

Your Sphinx is looking great, well done.

I think the best position for the end of the exhaust valve stem will be the centre of the " Starwheel " pivot, or just a bit before.

As I mentioned previously in this thread I had many an accident in the early days with the pushrod getting stuck under the stem in a reverse rotation scenario. Tube ignition being notorious for this condition!
I think you'll be the first customer to implement this design change.

Obviously the valve timing will be next on the list. With care, " textbook timing " can be achieved with the valve commencing at BDC and closing at TDC. You can however commence a little before but definitely not after.

Your piston to bore fit sounds perfect, a single ring would be my recommendation. ;)

Looking forward to seeing further progress.

Cheers Graham.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #82 on: August 09, 2019, 05:52:58 PM »
Hi Graham,

Been playing around with the star wheel and eccentric mechanism and think I have managed to get the timing just about right.
For those not familiar with the star wheel arrangement, I thought that the two attached photos might help explain how it works.
In picture 1, the push rod is held in the "miss" position, above the exhaust valve stem, by the higher part of the star wheel. In picture 2, the pecker arm has dropped in to the deeper part of the star wheel, bringing the push rod into line with the exhaust valve stem.
A tension spring pulls the eccentric arm down, ensuring that it remains firmly in contact with the star wheel. A spring washer behind the star wheel prevents it from being dragged backwards by the pecker arm as it returns.
« Last Edit: August 10, 2019, 03:47:30 PM by RayW »
Ray

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #83 on: August 13, 2019, 03:26:27 PM »
It became clear from turning the engine over with an electric drill, that I was losing compression through various leaking joints and through both valves, so I have spent the last couple of days making gaskets and re-grinding both valves. Things are now much improved and, from past experience, I know that compression will increase significantly when the valves have bedded in once the engine is running.

I have been working on the last major component today - the flywheel. The machining is now finished apart from cutting the keyway which I will have to do on the lathe as I don't own any broaches. There is also a lot of flashing that will require filing or grinding off to get an acceptable finish for painting. I don't usually use filler on my engines, but the main body casting in particular is very rough and will need quite a bit of grinding and filling to achieve an acceptable surface.


Ray

Offline crueby

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Re: Alyn Foundry Sphinx
« Reply #84 on: August 13, 2019, 04:06:58 PM »
Looking great - thanks especially for the explanation on the star wheel, that is a clever setup.
 :popcorn: :popcorn: :popcorn:

Offline Roger B

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Re: Alyn Foundry Sphinx
« Reply #85 on: August 20, 2019, 06:31:57 PM »
Looking good  :praise2:  :praise2: Your piston fit should be no problem, possibly even without an O ring.
Best regards

Roger

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #86 on: August 27, 2019, 04:58:57 PM »
Thanks guys for your comments. Just been in my sweltering workshop this morning finishing off the drip oiler (34 degrees C outside).
All the major components are now finished, apart from the ignition system which I am still thinking about. I will probably use a trembler (buzz) coil as I have a nice Ford one sitting on my desk as I type this.
Compression seems good with one Viton O ring on the piston, but I still seem to be getting some leakage past the inlet valve on the compression stroke. I do not understand how this is happening as I have tested it by immersing the whole inlet valve assembly (made of brass and stainless) in water and blowing through a tube attached to the gas inlet. There is no leakage from around the valve head itself, although there is very slight leakage from the air inlet holes, indicating that the valve is not shutting all of the holes off fully, allowing some of the air from the gas inlet hole to find its way to one or more of the air holes. I will be using a demand valve in the gas line, therefore gas will only be supplied on the suction stroke, so, in practice, there will be no leakage of gas from the air inlet holes.
On the compression stroke, the pressure should be forcing the valve onto its seat, but it appears that air is somehow escaping past the valve head and out through the air holes. I will have to try further lapping of the valve, but need to be careful to avoid blocking the 1/32" gas inlet hole with lapping compound.
 
Off on holiday in our motorhome (RV) next week so looking forward to a relaxing break away from the workshop.
Ray

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #87 on: August 28, 2019, 11:37:15 AM »
Good morning Ray.

It's nice to see your Sphinx nearing completion, well done. I particularly like the " hidden " cylinder liner!!

Your leakage is probably due to the use of dissimilar metals with different hardness. I recall my own problems. I remember having to " fine " polish using automotive rubbing compound or similar metal polish.

I'd suggest a couple of coats of primer before you start playing, just to protect the Iron from oil penetration.

Enjoy your holiday, cheers Graham.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #88 on: August 29, 2019, 08:00:23 PM »
Thanks  Graham for the advice. I will definitely try lapping in the inlet valve more when I get back from hols. I have already given the flywheel several coats of primer as you can see. There is already a bit of oil on the main casting where I have been running in the engine, but it seems to only be on the surface and should clean  off OK with white spirit.
Ray