ME 4761 – Sirius Piston Valve C**k up Corner

[Charles LamontParticipant @charleslamont71117]

I am surprised this 3-page article by Graeme Quayle has been published apparently without sanity checking the content.

This bloke has based the whole thing on an evident total misunderstanding of the Sirius’s valve design. His new valve ‘works’ on the wrong edges altogether.

I don’t have the drawings, so I can’t check the dimensions, but I think there can be little doubt that the original valve as drawn was fine. If there had really been a problem with it, it would have been known about long ago.

This needs a correction printing ASAP.

[JasonBModerator @jasonb]

I don’t have the Sirus drawings but if the Sun is anything to go by then  the bottom image in fig 3 has the valve in the wrong place, The widened 1/4″ section is not meant to be in the middle. This is the same way as the old Stuart drawing in Fig 1 has it.

Also Photo 4 shows the two full diameter parts of the new piston valve the same width but the drawing says the one at the end is 5/32 and the other 1/4″

Seems to have missed the point that it is inside admission and the inlet passage should nor be covered at any time

Looks like Cock up corner will be continuing into the new mag!

[Charles LamontParticipant @charleslamont71117]

Yes, its a sirius error.

[JasonBModerator @jasonb]

I am 99% sure that the Sirius is the same as the Sun and that the ports between cylinder and valve are machined. these are the important ones not the rough cored ones to the exhaust at the top and within reason the central hole to inlet is not an important size and could probably be anywhere from 3/16″ to 5/16″  and still work without problem using the valve as drawn on either of the Stuart drawings.

 

[JasonBModerator @jasonb]

100% sure now having looked at Tubal cain’s build in ME, the slots are milled and as he says

“The two slots correspond to the ports found on an ordinary slide valve”

So they are the important ones and the cast passages that the Author based his comments and the article on have nothing to do with the valve operation.

3 wasted pages really.

[Charles LamontParticipant @charleslamont71117]

Does anyone have a set of Sirius drawings we could ask for some dimensions to be checked ?

[JasonBModerator @jasonb]

I’ll scan the ones that were in ME in the morning as I’ve put the old mags away again but I have no reason to doubt them provided you use the machined ports through to the cylinders to base any calculations and assumptions on.

Just like on the Mystery engine over om HMEM the two upper cast passages on the sirius are just like the slots linking HP to LP and have no bearing on valve events.

[noel shelleyParticipant @noelshelley55608]

Jason, which editions of ME did TC do the write up in ? Thanks. Noel.

[JasonBModerator @jasonb]

Starts in Vol 168 No3914 and goes into Vol 169.

Would be interested if you have the valve drawing which wa sprobablt V169 No 3434 end of November 1992

[JasonBModerator @jasonb]

Well I have use the “valve chest” from Tubal Cains article as he does not mention any alterations to the lengthways position of the ports and the supposedly incorrect CAD drawn Stuart Piston Valve. All looks OK to me.

Top View shows the valve in mid position where both exhausts are open

Lower view shows it at full travel, inlet fully open and exhaust on the other side fully open.

At no point does the position of the cast passages at the top come into play.

Very similar to the position of the valve on the Sun

[Charles LamontParticipant @charleslamont71117]

You also show that the central steam inlet port is not part of the timing either.

I have the relevant parts of the drawing from a helpful guy on Model Engine Maker. I will be able to look at it all this evening.

[duncan webster 1Participant @duncanwebster1]

Having both exhausts open at the same time (exhaust clearance) might be necessary on a high speed engine, but it wastes a lot of steam. Would be interested in the opinion of a flash steam hydroplane exponent

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, here’s a scan of piston valve from Tubal Cain’s article, if anyone is interested.

Regards Nick.

[JasonBModerator @jasonb]

Thank’s Nick, that is how I have it drawn and it matches the CAD Stuart drawing.

 

[Clive FosterParticipant @clivefoster55965]

In WW2 the Sirius engine provided the motive power in the Alco “Firefly” clandestine radio set built for SOE and used by the French Resistance.  Given the production numbers involved it’s certain that all the drawings were sorted to production standards so any engine “just worked” and gave its expected power output after being built and assembled correctly into the Firefly unit. No time for typical Model Engineer faffing round to get the beast behaving under wartime conditions.

Given that it’s inconceivable that any functionally relevant errors of design in the valve gear made it through to the final drawings.

It’s possible, but unlikely, that significant errors may have crept in during later re-drafting. This seems unlikely given that significant numbers have been built from kits. Given the production history its as certain as can be that a Sirius built to the drawings will run fine.

Which doesn’t mean that valve gear improvements for more power or to adjust the power curve aren’t possible but as standard it will run well.

In the amateur engineering world there is always a risk of folk making errors or construction (or design) in something they do not fully understand and covering it up by introducing compensating errors. Thereby proving, to their satisfaction, the original designer was a dork!

its understandable that the originator of such changes would wish to publicise their success. After all he did get an engine that didn’t run well to go properly. But when it comes to publication it should have been written as “An Alternative Interpretation of the Sirius Valve Gear” in the tone of “Mine didn’t run well, this how I fixed it”. Which would have been quite unobjectionable albeit potentially misleading because its never explicitly said why it didn’t run well in the first place.

Publicising problems with established designs is always good. The resources for proper pre-production checking of drawings simply aren’t available to the amateur engineering world. Even the professionals don’t get all the errors! But a certain perspective is needed as to whether the builder or the draughtsman is in error.

Clive

[Graham MeekParticipant @grahammeek88282]

They say the proof of the pudding is in the eating. I made a Sirius engine back in the early 80’s to Stuarts drawings, which I still have. The drawing above matches those drawings. The engine performed faultlessly and was a nice engine to build.

Regards

Gray,

[JasonBModerator @jasonb]

It would have been usful to know how the engine was being run a swhat is good for one maynot be good for the other

Air or steam

Fast or slow

Loaded or unloaded

Any combination of the above

As the New Piston valve is based on the authors casting’s cored passages it would be difficult to for Stuarts to supply that as a “better” drawing as the position of the cores can vary from casting to casting. Far better to stick with ports that have been machined then provided it is built to drawing it will run.

 

[Charles Lamont]

On 22 January 2025 at 15:16 Charles Lamont Said:

I am surprised this 3-page article by Graeme Quayle has been published apparently without sanity checking the content.

…

I’m not!

Errors and uncorrected mistakes in Model Engineering drawings have been a persistent problem since Adam.  Many causes, all hard to fix.  I’ll leave it to Charles to list them and propose answers.   Be warned though, thousands have moaned about this problem for over a century and, so far, no-one has improved the situation.

As we live in an imperfect world, I advise Model Engineers to assume all plans contain errors.  Never assume that a hobby plan has been sanity checked by someone else.

Bad 2D plans are one reason I got into 3D-CAD.  3D modelling parts from 2D plans often exposes faults.   Much cheaper to find errors electronically than by making the part in metal!

Dave

 

[JasonBModerator @jasonb]

You have missed the point again Dave, there WERE NO ERRORS in the original drawing.

The author has completely got the wrong end of the stick as to what does what and has now compounded any uncertainty buy publishing his “correction”

I agree that drawing out a set of plans again is a good idea but if you don’t have the basic understanding of how a part should work then you are not going to spot errors or as in this case introduce ones of your own.

[John MCParticipant @johnmc39344]

As an apprentice, late 1970’s, I helped build a Sirius engine.  My employer needed a generating plant that produced no electrical interference, other than that of the generator.    I think the WW2 Alco generator was the inspiration.  We got it machined and running in less than two weeks.  It engine ran most working days for about a year with no attention other than the usual checks.  At some point I think it’s power output was checked, can’t remember the output.  It turned a Lucas motorcycle 120W alternator at, I think, 2500rpm.   All this suggests to me that the drawings are correct, or were correct at the time.

After the work was completed I would see the engine sat on a shelf in the stores until, one day, it wasn’t there…

One thing I cannot remember much about was the steam generator.  It was gas fired and water pumped in manually.

 

[noel shelleyParticipant @noelshelley55608]

I hope since the writer of the “Correction” in view of what has happened and will have been paid for his “efforts ” will see fit to donate his remuneration to a charity, may be a Prostate cancer one would be appropriate ? It would do no harm to issue an apology to Bridport Foundry/ Stuart Models as well?

Since the Firefly has been mentioned, it had an output of about 4 amps at 6volts to recharge radio batteries to power the filament circuit of the valve radios of the time. A later version, the Mk 814 was a single cylinder single acting engine also of Stuarts with an alternator and rectifier. This unit had a feed water pump and oil pump with a proper boiler as opposed to the firefly with its pot boiler which when it ran out of water had to drop the fire to refill after about 3 hours.  Noel.

[Jon LawesParticipant @jonlawes51698]

One quick point, yes, there has been an error made here. But can we be a little less scathing of the person who put the time and effort into writing it? They obviously believed they had something to share, and took the time to do so. How many of the vehement “string him up!” brigade have contributed something themselves? No matter how small, sharing a tip for example, it all makes up the magazine that people complain about mercilessly.

It reminds me of the chap who went round my locomotive at the club track pointing out all the ways it differed from the prototype, and how he would have “done it differently”. It turns out he had never used a tool more complex than a power drill.

Writing an article is difficult. Picking holes in it is considerably easier. Maybe those lamenting poor content could share some of their skills so we can make an even better magazine. Being scathing just puts would be contributors off.

 

[John MC]

On John MC Said:

As an apprentice, late 1970’s, I helped build a Sirius engine.  My employer needed a generating plant that produced no electrical interference, other than that of the generator.    I think the WW2 Alco generator was the inspiration.  We got it machined and running in less than two weeks.  It engine ran most working days for about a year with no attention other than the usual checks.  At some point I think it’s power output was checked, can’t remember the output.  It turned a Lucas motorcycle 120W alternator at, I think, 2500rpm.   All this suggests to me that the drawings are correct, or were correct at the time.

After the work was completed I would see the engine sat on a shelf in the stores until, one day, it wasn’t there…

One thing I cannot remember much about was the steam generator.  It was gas fired and water pumped in manually.

 

I’d love to know what he was using it for!

[JasonB]

On JasonB Said:

You have missed the point again Dave, there WERE NO ERRORS in the original drawing.

…

As that’s irrelevant I put it to my learned friend that he’s the one who’s missed the point!

It is, as I clearly stated, that all hobby drawings are untrustworthy until proved otherwise.  I’d be amazed to be told Jason works from unknown plans without doing his own sanity check.

🙂

Dave

 

[JasonBModerator @jasonb]

And that is why I said

I agree that drawing out a set of plans again is a good idea………………………………….

And with posts from the Likes of Graham who built an engine to the drawings woud seem to prove that the Sirius ones are OK

[Author]

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