Two Flash Steam engines

[Graham Meek]

Thank you both for your compliments.

The rotary valve does give additional exhaust relief, I have laid out the timing events for the engine. The valve rotation is clockwise and I have only labelled the "Steam" period for clarity. There is a short expansion period followed by the symmetrical exhaust period about BDC of the cylinder porting, which is overlapped by the rotary valve exhaust ports in the cylinder head followed by a small compression period.

This is the initial design as set-up by ETW, he does suggest in his article on this engine that the valve lends itself to modification. This is one avenue I hope to explore with the two cylinder version and if improvements can be made in steam economy with no loss of power then I shall be modifying the 3 cylinder version as well.

My best regards
Gray,

[pgp001]

Hi Gray

What a lovely pair of engines, nice to see you turning out some great work still.

I do have one thing I would like to warn you about though, and that is the use of builders sand in your blast gun.

Gray, please read this.
http://www.cdc.gov/niosh/docs/92-102/

I work in the blasting industry and come up against this all the time. You really need to use a fine "Silicon Carbide" grit instead of sand for this application.
You can find lots of good information in this document.
http://www.guyson.co.uk/assets/uploads/files/guyson_blast_media_guide.pdf

All the best
Phil

[Graham Meek]

Hi Phil,

Nice to hear from you again.

You are absolutely right with regards to the builders sand and it was good of you to point out the pitfalls. What I omitted to say was that I had rigged up a "booth" in which to do the sand blasting and had my shop vacuum keeping a depression in the booth, (I was on the outside the whole time). However I did not stop there as I wore a face mask which was for fine dust. The builders sand was a trial run to prove the system, now I know it works I shall be getting some glass beads as this is the medium I am used to from my time working with the Hospital. The "booth" is now a proper birch ply construction with a recovery system for the medium.

My best regards
Gray,

[pgp001]

Hi Gray

Just a thought, you might still want to give your parts an initial blast with an abrasive grit to remove any machining marks and blend the surface a bit.
This opens up the surface pores though and is prone to staining and absorbing dirt, so once you have the surface nice and even you go over it with the glass bead and that closes the pores up again.

I use the above technique when preparing items for being highly polished such as aluminium motorcycle engine covers or brass parts on model engines etc.

You probably already knew that though.

Phil

[Zephyrin]

Hi,
just a little comment on the steam diagram;
the admission period seems rather short, less than 120°, hence the 3 cylinder engine also may not be self_starting...
Cheers

[Graham Meek]

Hi Zephyrin,

The timing diagram was produced from the information given by ETW in his original article, so the timing events are of his design. I assume the Gemini two cylinder engine was intended for boat use, (flash steam hydroplane), and would have been started with a cord. While these timing events may not in theory be suited to a 3 cylinder, the above engine has not, as yet, failed to start on 30 PSI under it's (if you will excuse the term), steam.

I have only set the timing of the rotary valve visually as ETW describes in his article, (it may well be retarded at the moment). I have a more accurate means of obtaining the correct setting of the valve under construction. Using this setting tool will enable me to reset the valve to a previous known good setting, should the trailing of a new setting prove to be unsatisfactory.

Thanks for the tip Phil.

My best regards
Gray,

[Graham Meek]

I have just finished the parts for the oil pumps today. Not shown in the photograph of the pump parts are the non-return balls and springs. When I took the photograph they had not arrived. They did turn up later in the day and I have had the pumps working. At 1 mm bore and stroke they do not deliver a lot of oil, especially at half engine speed, still a little oil is better than a lot and much better than none at all. Provision in the design has been made to increase the bore and/or stroke of the pump if needed.

My best regards
Gray,

[Admiral_dk]

Hi Graham.

Wonderful engines 

Any chance of a link or a more precise reference to the crank design ?

Best wishes

Per

[Graham Meek]

Hi Graham.

Wonderful engines 

Any chance of a link or a more precise reference to the crank design ?

Best wishes

Per

Hi Per,

I take it that the crank in question is the 3 cylinder version?

If so then I do not have a link to the diagram I used to design the balance weights. The only reference I have is Fig 2.4 on page 23 of the book "Experimental Flash Steam", by J H Benson & A A Rayman, ISBN 0 85242 352 7. In the passage associated to the diagram it says that the design was presented to the Institution of Mechanical Engineers in 1970, by R M Palmer and was entitled "An Exercise in Steam Car Design". The original work was undertaken by Ricardo's of Shoreham, and that this was in response to a request from General Motors for an independent study.

When I was designing the crankshaft I did try to find out further information from Ricardo's and GM but both enquiries went un-answered. I also tried to look into the balancing of any 3 cylinder engine, but this did not yield anything positive. Most 3 cylinder engines that have been mass produced for automotive work use an additional balancer shaft, this was a complication I was trying to avoid.

Edgar T Westbury in his article on the Gemini does say that the balance weights on his engine were to stop the rocking moment associated with a twin cylinder as this can be more troublesome than the primary balance of each cylinder. It was therefore a little "Tongue in Cheek" that I added the balance weights to the 3 cylinder. I was not sure whether the weights would be too little or not enough. I have had the engine running as low as 10 PSI but it is not happy at this pressure, increase the pressure to 30 PSI and the engine smooths out dramatically.

I am happy with what I have done but would have liked to have under stood what a 3 cylinder engine really needed for balance, other than an additional shaft, but this may be the only alternative. If anyone knows more about this subject I for one would like to know more.

My best regards
Gray,

[Graham Meek]

Apologies for the double strike but I have just found this,

www.steamautomobile.com/archivepdf/SAv17n3.CV01.pdf

Page 24 of this document shows the engine in question, the document in itself looks to be very interesting.

My best regards
Gray,

[Admiral_dk]

Hi Graham

Thank you very much for the info and link. I must admit that I can't spot why it should work better than the traditional crank for a 3 cylinder engine - but that might just be me 

The major reason for putting in a balancer shaft is to avoid the rocking couples - this is done to 4 cylinder in-line engines too.

Best wishes

Per

[Graham Meek]

Hi Per,

I must apologise for not coming back sooner but I have been unable to access the web page for over 24 hours.

At first when I designed the 3 cylinder crankshaft I made no provision for the balance weights. Having seen the Willan's 3 cylinder engine in Vol 100 of the Model Engineer with it's "bent bar" type crankshaft I did wonder if the weights were really needed. It was not until I read the article again by ETW and his reference to the rocking couple being more troublesome than the primary balance of the engine that I decided to put them on. I am going to strip down the 3 cylinder engine shortly to install some gaskets. I might just try the engine after without the weights and see if they do make a difference.

I once had a Subaru with a 3 cylinder engine that too had a balancer shaft and I see Fiat have a balancer shaft on their "Twin-Air" engine.

My best regards
Gray,

[IanR]

A balancer shaft may be necessary for an ideally balanced engine, but Triumph Tridents (the 1960s - 70s ones) worked ok without them, as far as I know other bike engines such as Laverda Jota, Yamaha XS750, Suzuki GT750, Scott 1000, didn't have balancer shafts either. Just add weights as if it were 3 singles.

[Admiral_dk]

Totally correct IanR - but most modern 3 cylinder bike engines have the balancer shaft and as stated before even a lot of 4 cylinder ones have too now.

That shaft in those engines are in many cases used to do more than just being a balancer shaft - like driving the water pump etc.

[Graham Meek]

I have had a chance today to try the 3 cylinder engine with-out the balance weights fitted to the crankshaft. At the previous tick-over pressure of 20 PSI the engine does it's best to walk across the bench. Increasing the pressure just increases the rate at which the engine tries to escape. 

Refitting the weights returned the engine to it's old docile self, I therefore conclude that the fitting of the balance weights was well worth the effort.

(In both tests the engine was only restrained by the plastic air supply pipe with the sump pan resting on a paper towel on the bench)

My best regards
Gray,