New Modified Stuart 6A build

Read this first then introduce yourself here.
Lionel Connell
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New Modified Stuart 6A build

Post by Lionel Connell » Tue Oct 31, 2017 8:18 am

Hi Guys,
My name is Lionel Connell, I am an Australian now living and operating my own business in Da Nang city, Vietnam. Some time back I started building a Stuart 6A, I bought a complete set of workshop drawings by the late Alex Ritchie detailing all of the modifications that he made to the 6A, numbering more than 80 changes, I have also incorporated a number of changes of my own. I am a toolmaker of 40 years experience and I am fortunate enough to have my own comprehensive workshop attached to my business. My Stuart 6A build is about 90% completed and I expect to be finished around Christmas time this year. Although I have CNC machining capacity within my business, I have chosen the build the 6A entirely on manually operated machinery. I am in the process of uploading all of my building photos on my facebook page, they are not all up yet but I will get them up over the next couple of weeks. see the link below.

https://www.facebook.com/pg/steam.launc ... 7133109506


Any questions more than welcome, please have a look,enjoy the photos and follow my page to be notified of the updates as I upload more photos.

Cheers

Lionel
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cyberbadger
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Re: New Modified Stuart 6A build

Post by cyberbadger » Wed Nov 01, 2017 6:42 am

Lionel,

Great to hear from an Australian Steamer!

I respect and support your deliberate use of more manual machining methods. ;)

What are the main purposes/features of all the modifications?

Great work from the pictures and welcome to the forum!

-CB
Lionel Connell
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Re: New Modified Stuart 6A build

Post by Lionel Connell » Wed Nov 01, 2017 8:11 am

Hi CB,

Looking at the various steam boat registers, the Stuart 6A is by far the common engine fitted to steam launches in the 1-23ft category. Over the years many operators have found various problems with the reliability of the engine. The 6A was designed primarily as a model and as such little of the design detail was carefully considered, the engine has many short comings compared with engines that were built commercially for use in steam launches. The late Alex Ritchie built many 6As on a commercial basis and as such he needed to ensure that the engines gave long reliable service. Alex made many changes to the design, most of the modifications were made to improve longevity, and some to creat a smoother running engine.

All of the bearing surfaces have been increased in area.
More modern types of bronze were used rather than simple gun metal.
Many of the steel parts have been case hardened or through hardened.
Aluminium pistons were used in conjunction with bronze filled PTFE hydraulic rings.
The slide valves are balanced and the slide faces increased in area.
The engine was made taller to improve the stroke to conrod length ratio which improves valve timing but also reduces the loads on the cross heads and reduces the bearing surface velocity of the little end.
The rear pillars are not only taller but also wider so as to increase the cross head bearing width and length.

The list goes on and on.

Despite the changes made by Alex, the engine timing events remained terribly out of balance and inefficient. I 3D modeled the entire engine, every last part, in Solidworks. By doing this I can run the engine simulate the valve events exactly. I changed the suspension for the Stevensons from side suspended to center suspended, the way that Stevensons actually designed it, and the valve events are now perfectly balanced.

The water pump has been moved from the end position where the conrod is way to short, to behind the second pillar and lever driven exactly the same as the vacuum pump. I have also added a mechanical lubricator with 10 individual pumps.

I have seen quite a number of references on the WEB dicussing the modifications made by Alex Ritchie and most note only the increased height of the engine and perhaps the use of hydraulic rings, in fact the modifications number more the 80.

cheers

Lionel
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Lopez Mike
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Re: New Modified Stuart 6A build

Post by Lopez Mike » Wed Nov 01, 2017 5:53 pm

More than one person here in the U.S. has found it worthwhile to increase the valve rod diameter.

A wonderful engine in my humble opinion. (Barbara breaks out laughing whenever I use that expression.)
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Re: New Modified Stuart 6A build

Post by marinesteam » Wed Nov 01, 2017 6:51 pm

Lionel,

Welcome, Your 6A is going to be jewel. Looking forward to more pics (to make me feel inadequate in my machining capabilities) :-)

Ken
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Re: New Modified Stuart 6A build

Post by Lionel Connell » Thu Nov 02, 2017 12:19 am

Thanks Ken, I will get some more pictures up soon.

I have noted mention of some people increasing the valve rod Dia, I had already made the rods from 316SS, but increasing the size would be relatively easy. I have supported the valve rod at the top in a bushing, and the valves are partially balanced.
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Re: New Modified Stuart 6A build

Post by barts » Thu Nov 02, 2017 12:57 am

Lionel Connell wrote:Thanks Ken, I will get some more pictures up soon.

I have noted mention of some people increasing the valve rod Dia, I had already made the rods from 316SS, but increasing the size would be relatively easy. I have supported the valve rod at the top in a bushing, and the valves are partially balanced.
You may wish to consider 17-4 ph stainless for valve rods; hardened somewhat, it machines nicely, has the corrosion resistance of 304L but it's quite readily hardened to R C38 and
has yield points above 100ksi. It's available pre-hardened as well from many suppliers if you don't have heat treat facilities; since it's a precipitation hardening allow it's very simple to heat treat if youi can hold at temp for a while. https://www.beststainless.com/17-4-ph-s ... steel.html

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
Lionel Connell
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Re: New Modified Stuart 6A build

Post by Lionel Connell » Thu Nov 02, 2017 2:48 am

Where I am in Vietnam specialty alloys are harder to come by in small quantities so I have to select from what is available. I would have used hard chromed 4140 hydraulic piston rod shaft as my first preference, this is what I used for the piston rods, but I could not buy it in less than 16mm dia.

316SS is 110 KSI without any need for heat treatment, and has better corrosion resistance than 304.
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Re: New Modified Stuart 6A build

Post by barts » Thu Nov 02, 2017 6:34 am

I'll grant you the better corrosion resistance, but the numbers I see for 316 indicate
it's not nearly as strong as heat treated 17-4.

https://www.beststainless.com/316-316l- ... steel.html
https://www.beststainless.com/17-4-ph-s ... steel.html


- Bart
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Lionel Connell
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Re: New Modified Stuart 6A build

Post by Lionel Connell » Thu Nov 02, 2017 7:31 am

Yes I agree, but as I stated in my last post, I cannot get it here so it is a pointless debate.
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