Author Topic: 21st Century Stuart "Simplex"  (Read 1021 times)

Offline Jasonb

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21st Century Stuart "Simplex"
« on: December 31, 2021, 04:23:30 PM »
Just time to squeeze another little one in before the end of the year :cartwheel:, these small pond boat engines are getting quite addictive :-[

This time the subject is the Stuart Simplex which was produced from 1924 to 1928 and only available as a machined kit of parts or complete engine so no drawings were ever made available. I went with the "New Simplex" which was introduced in 1926 which can be recognised most easily by the trunk guide, the earlier engines having various forms of bar guide for the cross head.



I managed to find a few images on the net and was lucky enough to be given a few main dimensions by someone on the Stuart Models Steam Engines Facebook Group so armed with those a few evenings spent with Alibre had a working design. As per the previous engines I updated to metric but kept the size approx the same so the 5/8" bore x 5/8" stroke became 16mm x 16mm







Looking back at the dates on my photos I started this one on the 17th Dec and got it running yesterday just in time for a quick strip and paint so it could be assembled and videoed today. I did make use of the CNC on a few parts but with only minor alterations to one of them all could be done on manual machines. There are quite a few parts even though it is not that big an engine and some do get a bit fiddly to handle but at least it does not take up too much shelf space ;)



And when they are all put together it comes out like this.









I was happy that it started straight away as soon as the air was connected after a quick sideways knock to get the valve to sit down on the port face and just needed a slight reposition of the eccentric to get it running cleanly and faster. Most of the footage in the video was with the compressor regulator reading 5-6psi and as you will see towards the end of the video it runs quite slowly for what is a "high speed" engine. Though with the regulator opened up a bit to 20psi it was happy spinning over at 1800rpm as you will see if you watch to the end.

iHxsC5VWmnQ

Offline Dan Rowe

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Re: 21st Century Stuart "Simplex"
« Reply #1 on: December 31, 2021, 04:49:48 PM »
Nice, I really like the crankpin design.

Cheers Dan
ShaylocoDan

Offline crueby

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Re: 21st Century Stuart "Simplex"
« Reply #2 on: December 31, 2021, 06:53:47 PM »
Nifty little engine!  Runs very well.  Does it have a piston ring or just oil grooves?

Offline Jo

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Re: 21st Century Stuart "Simplex"
« Reply #3 on: December 31, 2021, 07:13:50 PM »
That's a nice simple model engine  :)

It is very similar to John Bertinat's Trojan Mk2 (GA attached), full drawings for John's engine are available for free on line or you can find them in ME back in 1978.

John's version uses the available Reeves castings  :Love: for those of you who might not have a CNC mill.  :mischief:

Jo
Enjoyment is more important than achievement.

Offline Jasonb

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Re: 21st Century Stuart "Simplex"
« Reply #4 on: December 31, 2021, 08:19:20 PM »
Dan, the bored out crankpin was a feature of the original and seems to help with smooth running a seven at high speeds the engine does not move about very much unlike the Husky I did recently which is all over the place even at slow speed.

Chris I just went with two small oil grooves in the aluminium piston as I have with all these pond boat engines which seem to work OK

Jo yes the Trojan is quite similar both Westbury's original which is more like the early ones with it's rod guides and Bertinat's Mk2 with it's tubular trunk guide closer to teh "New" one though I do personally find his trunk guide looks a bit chunky.

As I said a CNC is not required and infact it would be possible to do it all manually but one slight change to the finished look of the base would make it easier and one other additional change would make it very simple.

Not easy to spot the change as you can see from this.



The other thing that would simplify it even more is if the raised round bosses were done by cutting shallow counterbores and JBWelding in some short lengths of round stock otherwise it's just a bit more work and a few repositions on the rotary table to mill each round boss from the solid block.

I've already had a few people interested in drawings so will likely make a set available to those who want to build it and they will have both options shown.

Being fairly simple it will also appeal to beginners so that is another reason I have updated it to metric as there are many who prefer that to imperial and BA fixings or if you go with Reeves' Mk 1 small whitworth fixings :rant: Plus being cut from solid there are none of those hard or misshapen casting issues and at about 1/4 of the price you would have enough pocket money to buy the materials for the other three of these that I have done.

Offline RReid

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Re: 21st Century Stuart "Simplex"
« Reply #5 on: December 31, 2021, 08:24:42 PM »
That really is a little sweetie!  :cheers:
Regards,
Ron

Offline propforward

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Re: 21st Century Stuart "Simplex"
« Reply #6 on: December 31, 2021, 08:27:45 PM »
Very nice little engine. 👍
Stuart

Forging ahead regardless.

Offline Admiral_dk

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Re: 21st Century Stuart "Simplex"
« Reply #7 on: December 31, 2021, 09:50:54 PM »
Nice way to finish the year Jason  :ThumbsUp:

Runs and sounds good too  :cheers:

Per

Offline steam guy willy

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Re: 21st Century Stuart "Simplex"
« Reply #8 on: January 01, 2022, 02:29:57 AM »
Hi Jason , Lovely little engine and interesting construction ...with an economy of parts ,...is the crosshead guide tube pressed into the top plate or is it a one piece casting ?? Hi Just had another look and seen how it was constucted !! would the original have been a casting or a really good press fit  with no loctite
 ??

Willy
« Last Edit: January 01, 2022, 02:39:24 AM by steam guy willy »

Offline Jasonb

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Re: 21st Century Stuart "Simplex"
« Reply #9 on: January 01, 2022, 07:38:21 AM »
Thanks for the comments

Willy, the original was cast as part of the entablature/front cover in gun metal.

I mabe my guide from 12mm steel boring and then reaming a 10mm hole right through and then milling the slots.



I then turned a spigot on the end of some CI bar using the guide as a gauge to get a firm push fit, after shaping the entablature and parting it off over thickness the two were loctited together.



To ensure the trunk guide was perpendicular to the cylinder mounting surface I then held the assembly in a collet and finished the face and cylinder location spigot to thickness



It could have been done from a single length of steel, CI  or even GM bar bar but that seemed a bit wasteful of material and would have needed a long series milling cutter for the guide slots. I did use the CNC to shape and drill the entablature but easy enough to do on a manual mill as it is just a case of milling the basic "H" shape, drilling a few holes and then rounding the 4 corners which could be done on a rotary table or with filing buttons.

J

PS anyone spotted the difference between those two bases yet?
« Last Edit: January 01, 2022, 07:42:50 AM by Jasonb »

Offline Jo

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Re: 21st Century Stuart "Simplex"
« Reply #10 on: January 01, 2022, 07:50:07 AM »
I mabe my guide from 12mm steel boring and then reaming a 10mm hole right through and then milling the slots.

I see what you mean when you said I do personally find his trunk guide looks a bit chunky. John's Trojan 2 is the same as the Stuart 10H/V with cross heads the same diameter as the piston at 16mm diameter meaning that the outside of the guide is 19mm. So it is massive in comparison.

Jo
Enjoyment is more important than achievement.

Offline Jasonb

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Re: 21st Century Stuart "Simplex"
« Reply #11 on: January 01, 2022, 08:48:12 AM »
Yes John and Westbury went with a much more complex conrod with the forked end so needed the larger bore of 5/8  which as you say is the same dia as the Trojan cylinder. The Stuart 10V is a little better with 3/4" cylinder and 16mm trunk guide plus the fact it is a taller engine make sit look more in proportion.

I did deliberate for some time trying to decide if the Simplex was 9/16" on on OD with maybe 7/16" ID but in the end went with the 12/10 combination as I did not have an 11mm reamer (or want to cheat with 7/16) and being quite a long small dia bore there was a risk of a skinny boring bar producing a tapered hole.

If anyone wants to look at the Trojan Mk11 then Model Engineer have it hidden away in their documents just change the url to part 2 for the other half

https://www.model-engineer.co.uk/sites/7/documents/trojan-mk2-part1.pdf