Author Topic: Alyn Foundry Sphinx  (Read 4781 times)

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #60 on: June 20, 2019, 11:03:55 AM »
Made a start boring out the valve chest casting and things did not go well! The valve stem is 0.25" diameter, so, having marked the approximate centre at each end, I decided that I would bore a 6mm pilot hole right through the casting, starting from the inlet valve (bracket) end.
The casting is quite an awkward shape to hold and despite thinking that I had it mounted absolutely vertically in the milling machine vise, I clearly didn't as the hole was way off centre at the exhaust valve end.
The only way I can see to rectify this is to enlarge the valve stem hole, fill with a cast iron plug fitted with JB Weld, then re-drill.

Ray

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #61 on: June 20, 2019, 11:41:30 AM »
Could just fettle the outside of the casting so it looks more central and make the two mounting holes a good clearance so you can mount it with the valve hole horizontal.

For something like that I would have slipped a couple of pins into the bolt holes and set then on the vice jaw or parallels to the hole was at right angles to them. Alternatively with the mounting face and bolt holes done screw it to a true block and use that to hold it by for the other ops so easy to line it up in all 3 axis.

Any decision on the strap material yet?

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #62 on: June 20, 2019, 12:27:28 PM »
The valve hole is horizontal but angled in towards the body of the engine, so I suppose I could get it parallel by slightly angling the mounting surface but I am not really happy doing it that way. The real problem is that I started boring out the other end after adjusting the casting in the vice to correct the vertical position, as a result of which the valve hole is not parallel to the larger bore meaning that the valve would not sit squarely on its seat. I still think that the best solution would be to bore and plug the valve hole then re-drill. The other consideration is that the extension tube to support the longer exhaust valve also needs to be bored perfectly in line with the valve chest.

Ray

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #63 on: June 20, 2019, 01:13:30 PM »
In that case I would open it up right the way through to 3/8" BSP tapping size which could be done in the 4, jaw with a boring bar so you don't get any wandering. Or you could go that size most of the way through but then reduce down to say 0.518" dia which would give a shoulder for the sleeve to sit against and end of sleeve can be threaded 1/4" BSP for the extension

Then turn up an insert, reamed 1/4" and with the valve seat turned at the same setting with the top slide angled which will keep those two concentric. Finally reverse it round and machine the smaller dia and thread end
« Last Edit: June 20, 2019, 01:23:21 PM by Jasonb »

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #64 on: June 20, 2019, 03:44:25 PM »
Thanks Jason, That's definitely a possibility, but given the difficult shape of the casting, I'm not sure how you could set it up in the 4 jaw to run true so that the centre points at each end were exactly aligned with each other.

The tapered nipple on the end of the casting was quite mis-shapen so I have removed it. Measuring up on the cross section drawing, the distance between the exhaust port hole and the end of the casting is only about 0.6". I reckon if I just drill and plug that short section, once I have bored out the 3/8 BSP part and the 0.375" section, I can then make up a drilling guide to fit in there to drill the 0.25" section. I would extend the plug beyond the end of the casting and thread 1/4 BSP for the extension.
Ray

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #65 on: June 20, 2019, 04:27:49 PM »
Hi Ray.

Now you know why Jo spends so much " fondling " time....  :)

Never mind, perhaps as you're  going to add the extension you could just bore through at 1/4" BSP tapping and put the 1/4" valve stem hole concentric with the new threaded insert.

As it's on the LP side Loctite would be more than adequate as a retainer.

Cheers Graham.

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #66 on: June 20, 2019, 04:58:29 PM »
Quote
Thanks Jason, That's definitely a possibility, but given the difficult shape of the casting, I'm not sure how you could set it up in the 4 jaw to run true so that the centre points at each end were exactly aligned with each other.

You could always clamp it lightly  to an angle plate on the faceplate and pop a dead ctr in the spindle, line one end up with that and the other with the tailstock ctr before tightening the clamps.

Too late for the trick of using a drill bit in the lathe spindle and applying pressure with a tailstock ctr at the other end to get the two punch marks to line up.

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #67 on: June 22, 2019, 02:04:08 PM »
Further to what I said in the last post, flange machined flat and both ends of casting marked out at the same setting with a point in the mill and height gauge, casting having been adjusted in the vice to get best positions before milling flange



Fixed loosely to an angle plate then held between ctrs in punch marks, 1-2-3 blocks used to set angle plate parallel to faceplate, tighten casting to angle plate.



Now set the casting to run true knowing the back end will also be running true.



Face and start off with a sharp stub drill, at this point F1 Qualifying stopped play



Also my strap ended up at 1.720" so just put the eccentric into the soft jaws and reduced flanges to 1.75"

« Last Edit: June 22, 2019, 02:07:58 PM by Jasonb »

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #68 on: June 23, 2019, 05:37:39 PM »
I decided to rectify my error with the exhaust valve, by boring out the valve chest casting to accept a steel bush which will act as the valve seat and guide. The main hole was bored to 19/32" (3/8 BSP tapping size), with the hole for the bush 17/32". I also made up a 2" long extension to support the long exhaust valve stem. The extension is bored out to accommodate the valve spring and collet.
I will not Loctite the bush in position until I have drilled the 20 degree sloping hole from the mounting face so that I can check exactly where it comes out in the larger bore, to ensure that the exhaust valve bush is deep enough.

« Last Edit: June 23, 2019, 05:42:21 PM by RayW »
Ray

Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #69 on: June 23, 2019, 06:15:08 PM »
Hi Ray.

An admirable recovery, well done!

Cheers Graham.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #70 on: July 05, 2019, 05:06:44 PM »
Not much done in the workshop lately due to painting and decorating taking priority during the current heatwave.
Finally got back in there today and re-made the inlet manifold, after having to scrap the first attempt when the 1/32" drill bit for the gas inlet snapped in the hole and totally defied all efforts to remove it. I just need to make the inlet valve now, then sort out inlet and exhaust springs, then that will be the valve chest assembly complete.
The inlet valve spring is supposed to be tapered. Has anyone any tips on how to make a tapered spring?
Ray

Offline Jasonb

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Re: Alyn Foundry Sphinx
« Reply #71 on: July 05, 2019, 05:47:52 PM »
Wind it around a tapered mandrel







I took a different route and used a smaller dia spring as per Grahams engine in his video, also did not like the holes breaking out of the tapered section


Offline Alyn Foundry

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Re: Alyn Foundry Sphinx
« Reply #72 on: July 06, 2019, 06:35:25 PM »
Hey Guys.

Nice work!

I've been besides myself for the last several days my relief came yesterday with a visit to the Dentist.

Ray, I'll be popping into the Post office next week, sorry for the delay.

Cheers Graham.

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #73 on: July 06, 2019, 08:47:38 PM »
Sorry to hear you have been suffering more dental problems Graham. No rush with the casting. Post it when you are feeling fitter. As I said earlier, there are plenty of other bits for me to be getting on with in the meantime.
Ray

Offline RayW

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Re: Alyn Foundry Sphinx
« Reply #74 on: July 24, 2019, 03:23:26 PM »
I have now completed the crank webs and just received some silver steel to assemble the crankshaft. While waiting for the steel to arrive, I decided to start machining the piston. When I got the casting from Graham, he told me that it was actually a Robinson one, a fact borne out by RO cast on the side. We both thought that it would be fine for use on the Sphinx, but what Graham had forgotten, and what I did not realise at the time, was that the Robinson piston is something like an inch shorter than the Sphinx one.
I had already started to make the connecting rod, based on the between centres dimension of 6.25" as per the drawing. As can be seen from the attached photos the shortness of the piston meant that the top would be nowhere near the end of the cylinder when at TDC which would dramatically affect compression.
Having discussed possible solutions with Graham, it came down to three possibilities:
1) Extend the length of the connecting rod
2) Extend the piston casting
3 Make a completely new piston from scratch

I decided to go with option 2, having found a suitable offcut of cast iron bar of ideal dimensions.I machined down the existing spigot on the top of the piston to 0.5" diameter by 0.25" long, then bored out the extension piece to match. I also bored 0.25" through the centre of the piston and drilled and tapped a blind hole in the centre of the extension piece. I then inserted a 1/4 BSF dome-headed socket screw through the piston and into the extension piece and screwed the two together tightly, with a thin layer of JB Weld between the parts and around the head of the screw inside the piston.
I will now wait for everything to set hard before turning down to final size and cutting the piston ring grooves.
« Last Edit: August 05, 2019, 08:23:14 PM by RayW »
Ray