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[MichaelK]

Hi. I've just bought one of these steam engines.
The build is going well until now. Maybe someone who has built one came across the same problem, or someone with better engineering knowledge than myself can help.
Building the valve gear assemblies, there are 2 small bushings that go into the offset links and into the 2 hole links. The same bushings go into the Eccentric straps as well.
Should these bushings be a tight fit in the respective links, (which means the links move by pivoting on the screws) or are the bushings loose enough to rotate in the respective links(which means the links move by pivoting on the actual bushing)
When I tighten the screws, the links won't move, and if I leave them loose enough to move, I worried that they might come loose in normal usage.
Hope someone can help, before 1) I get too far into the build, and have to unbuild the whole thing, or 2) I start the engine up and things go really, really pear shaped.
Thanks
Mick

[kno3]

Can't remember how tight they were when I've assembled mine, but I suggest tightening the screws only so much as to have free movement in all linkages. If needed you can tighten them later on too, as they are accessible without disassembling he engine.

[andywright]

I think the bushings are to protect the alloy arms they fit in, the bushes take the wear away from the alloy parts, I think its OK if they are a relatively loose fit.
Andy

[tobyker]

This confused me too, and I seem to remember that the instructions tell you to file the bushings down until they are flush with the aluminium (aluminum?) links. This only deepens the mystery, as I'd think that the bushes should be fixed to give the links a larger bearing area, and the bushes don't have to wear od the threaded steel screws. One of mine did come loose while I was running it in with the bicycle track pump and rice pudding tin receiver, but I tightened it up again and it's not loosened again despite far longer running sessions with my new compressor. You could of course ask Robert Graham, and let us all know what he says!

[MichaelK]

Thank you folks.
I've now got 3 different opinions\views\usages!!!!
I've emailed Robert Graham twice on the subject, still no answer from the man who should know the definitive answer. Apparently this is a part time occupation for him, so a reply might take time. Meanwhile I can continue lapping.
Mick

[Circlip]

Bushes are normally fitted in high wear locations so that the bush or its pivot can be replaced when worn. Which is easier to replace, a brass/bronze/gunmetal sleeve and pivot screw or the bit the bush pushes into??

  Regards  Ian.

[MichaelK]

Thank you folks.
I hav'nt heard from the manufacturer yet.
I've got the little engine running (on air), and guess what????
Pivots unscrewing!!!!
So I pulled the valve actuating arms off, and used Loctite to secure the screws.
I'll find out tomorrow if it works.
In passing, the bushes are meant to be a tight fit in the variouse arm etc, and the wear happens on the flange of the bushing.
Mick

 

[MichaelK]

Update.
A really small(really, really  small, like on the end of a small dia piece of copper wire!)   amount of Loctite has cured the loose buhsings etc.
Now it's leaking air.
I pulled the top half apart, leaving all the valve actuating apparatus in place. (it is quite easy really!) , cleaned it all ,and re-assembled it using Loctite gasket replacement. Apart from a little leak from the bolts next to the air-ways, (fixable with careful application of Loctite)
   Air leaks out from between the under side of the cylinder mount (the square-ish bit of aluminium) and the top of the crosshead guide(the brass bit that holds the sliding bit that screws onto the bottom of the piston). I'm thinking it could be comming down via the bolts that hold the crosshead guide ot the underside of the cylinder mount.
Before I pull it all apart again tomorrow, has anyone had a similar problem? Does anyone have a solution??
And befor anyone asks, I am quite good with small mechanical bits and pieces!
Thanks
Mick

[gondolier88]

Sounds more likely to be the bottom cylinder cover gland if it's coming down the cross slide.

Turn the engine upside down and put a thick soapy solution on it with pressure on the piston- this shouldl show you were the air is leaking from.

THEN WASH THE ENGINE IN WARM WATER AND THOUROUGHLY OIL IT EVERYWHERE!

Greg

[kno3]

Update.
A really small(really, really  small, like on the end of a small dia piece of copper wire!)   amount of Loctite has cured the loose buhsings etc.
Now it's leaking air.
I pulled the top half apart, leaving all the valve actuating apparatus in place. (it is quite easy really!) , cleaned it all ,and re-assembled it using Loctite gasket replacement. Apart from a little leak from the bolts next to the air-ways, (fixable with careful application of Loctite)
   Air leaks out from between the under side of the cylinder mount (the square-ish bit of aluminium) and the top of the crosshead guide(the brass bit that holds the sliding bit that screws onto the bottom of the piston). I'm thinking it could be comming down via the bolts that hold the crosshead guide ot the underside of the cylinder mount.
Before I pull it all apart again tomorrow, has anyone had a similar problem? Does anyone have a solution??
And befor anyone asks, I am quite good with small mechanical bits and pieces!
Thanks
Mick

Did you use the provided paper gaskets when assembling the engine? I f not, you need to do very careful polishing of the surfaces to get them steam-tight. I recommend using the gaskets, it's much easier.

[MichaelK]

Thank you gondolier88 and kno3,
Yes, I used the supplied gaskets when I first put the engine together. That left a dark ring around the cylinder heads, from the (?) neoprene "O" rings. Also a lot of black stuff all over the engine. Not a major problem!
When I pulled it apart, I re-lapped all the bits with 1200 wet & dry, so they are now quite shiny.
After putting it all back together, using gasket replacement (Loctite) on the top of the cylinder, bottom of the cylinder and also on the top of the crosshead guide, it is now leaking from the under side of just one cylinder. A little bit from the cylinder head, (fixable!!!)
When I put it back together,looking closely, the "land" between the cylinder bore and the bolt hole varies around the diameter of the cylinder that is leaking. On one side it's about 1and half mm, on the other it's almost zero mm. Therefore,air can go from inside the actual cylinder, through the bolt hole, and escape down and out from the joint of the crosshead guide and the cylinder mount.
I've emailed the manufacturer in the US regarding the issue of the bushings, so far without a reply.
Has anyone had a problem with questionable machining of these engines?
It is now getting close to the stage where I'll have to ring the man on the phone to try and sort out this problem.
Thank you,
Mick

[derekwarner]

Hi Mick......Dee Why is just up the road & across the water a bit from John in Balgownie & me in Corrimal   or 100 km as the crow flys

Keep us posted on your build...as many here love steam   .....

I would hope "from the (?) neoprene "O" rings" is not correct as Buna/nitrile/neoprene is only OK for say 98 degrees C.....in wet dynamic applications

Typical model steam boiler discharge temperatures @ 2.5 Bar will be approx 150 degrees C..........from this one could expect the engine inlet manifold temperature to exceed 115 degrees C ... a simple check with a digital pyrometer will substantiate the actuals......

Just re-reading your posting,...it sounds like your pre machined kit has 1.5 mm clearance between a cylinder bore & the major OD of a cap tapping on one side ........& then near ZERO clearance between the bore & the tapping's @ 180 degrees........

Or in lay terms ....the PCD for the cap tappings is not concentric with the cylinder bore ....Derek

Derek

[kno3]

Mick, my Graham engine was perfect, I had no trouble with it. Sounds like yours might have a manufacturing problem, perhaps you need a replacement cylinder.

[gondolier88]

A picture would really really help here!

[MichaelK]

Thank you people,
I thought they were neoprene, obviously not, but they are the O rings supplied with the kit.
I was down in the Shire on Sat. could have kept going! Where and when do you sail?
Next time I pull the engine apart, I'll try and take a photo of the offending part.
At the moment the engine is running as sweet as a swiss watch (on air) I'll do a leakage test tomorrow, and then probably have to telephone the states at some time Mon night to try and get onto the manufacturer.

Mick

[gondolier88]

I just remebered what steam o-rings are made of, I can never remember the name and last night was no exception!- You want 'Viton' o-rings

Greg

[derekwarner]

Or silicone........ Derek

[gondolier88]

Is that so Derek, are they pure silicone?

Greg

[MichaelK]

Viton sounds about right.
I used Viton-A o rings as the oil seal on Ducati Motorcycle valve guides many years ago, There is a lot of heat and friction in a cylinder head!
Mick

[derekwarner]

Greg - yes - Viton is technically rated to 205 degrees C, however in a wet dynamic application this is reduced to approx 195 degrees C - I fully acknowldge Viton [FPM] is more readily available over silicone grades - I understand that one French model steam engine manufacture uses silicone O-rings & teflon back ups..... here are a few notes on silicone O-rings courtesy of a GOOGLE serach ......Derek 

O-Rings are available in five different materials from Scientific Instrument Services. Each type has its advantages and disadvantages as listed in the O Ring Comparison Chart. Silicone is a popular O Ring which is commonly red in color. they are popular for use in scentific instruments such as GC injection ports which use high temperatures.

SILICONE RUBBER (Si) Typical Trade Names:

•Rhodia Rhone Poulenc
•Silastic Dow Corning Corp.
•No trade name General Electric
•No trade name Stauffer Chemical Company
The silicones are a group of elastomeric materials made from silicone, oxygen, hydrogen and carbon. As a group, the silicones have poor tensile strength, tear resistance and abrasion resistance. Special compounds have beer made which have exceptional heat and compression set resistance. High strength compounds have also been developed but their strength does not compare to conventional rubber. Silicones possess excellent resistance to temperature extremes, Flexibility below - 175 degrees F (- 114 degrees C) has been demonstrated. The maximum temperature at which silicones are recommended for continuous service in dry air is 450 degrees F (232 degrees C). Silicone's retention of properties at these high temperatures is superior to other elastic materials, Silicone compounds are not normally recommended for dynamic sealing applications due to relatively low strength and high coefficient of friction. Many silicone compounds have a higher than normal mold shrinkage that results in finished parts being under mold shrinkage when produced in standard molds.

[steamboatmodel]

I do remember that there was one type of O ring material that when heated above a certain temperature turned into a sticky mess that was a strong acid (Hydrofluoric?). I have been trying to find the information on it but no luck.
My luck has changed "Hydrofluoric acid is a known hazard in car engine fires, forming when Viton o-rings and hoses are exposed to temperatures in excess of 400°C."
During normal use we should never reach 400°C, but if you do and it turns sticky DON'T TOUCH IT. http://www.search.com/reference/Hydrofluoric_acid
Checking on some O ring site I found that Viton is NOT recommended for Hot Water and Steam. They recommend EPDM for steam, but not for Petroleum oils and fuels http://www.marcorubber.com/materialguide.htm
Regards,
Gerald.

[gondolier88]

That's very interesting gerald, thanks. I wonder if perhaps we are both right- it might not be classsed as suitable for steam as anything above 300psi would be too hot and if it's superheated at any pressure it would become sticky too.

However, that wouldn't explain why it's not suitable for hot water.

I know the name 'Viton' from reading steam catalogues and they reccomended them- can't remember which cat' it was, and as the little man is asleep on me and they're all packed up I can't find out!

Did your site say which materials were best suited?

Greg

[andrewh]

Hi, Chaps,

I may be able to throw a little light on the rubbers issue

Viton is the common fluoroelastomer, and is pretty resistant to everything (except steam and HP water)  Can't remember why, but it probably hydrolyses. 
Above about 410 degC it dissociates to liberate free fluorine, which then diissolves in any available water to give Hydrofluoric acid (HF).  THIS IS AN EXTREMEMLY DANGEROUS SUBSTANCE - IT DISSOLVES FOR EXAMPLE, GLASS AND HUMANS!

The general elastomer for steam and Hot water is EPDM which will handle about 180 deg C forever and higher temperatures for shorter times.  It is not bothered by light or ozone  (it has very little resistance to oils and greases)

Silicone is pretty good as well, and has even better temperature resistance, and is slightly better with the oils, etc

hope this helps
andrew

[HS93 (RIP)]

Hi, Chaps,

I may be able to throw a little light on the rubbers issue

Viton is the common fluoroelastomer, and is pretty resistant to everything (except steam and HP water)  Can't remember why, but it probably hydrolyses. 
Above about 410 degC it dissociates to liberate free fluorine, which then diissolves in any available water to give Hydrofluoric acid (HF).  THIS IS AN EXTREMEMLY DANGEROUS SUBSTANCE - IT DISSOLVES FOR EXAMPLE, GLASS AND HUMANS!

The general elastomer for steam and Hot water is EPDM which will handle about 180 deg C forever and higher temperatures for shorter times.  It is not bothered by light or ozone  (it has very little resistance to oils and greases)

Silicone is pretty good as well, and has even better temperature resistance, and is slightly better with the oils, etc

hope this helps
andrew

what is the problem with Viton and WD40 does it damage it

thanks
Peter

[gondolier88]

Hi, Chaps,
...
The general elastomer for steam and Hot water is EPDM which will handle about 180 deg C forever and higher temperatures for shorter times.  It is not bothered by light or ozone  (it has very little resistance to oils and greases)
...
andrew

Would that be like in a steam engine cylinder?

Greg