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piston rings or ptfe packing

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Kevin Bennett27/01/2012 19:37:57
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193 forum posts
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Hi am still making my scratch build of a Stuart 10V from a book what is best with a brass a piston rings or ptfe packing for a Stuart 10V

Thanks Kevin

Dusty27/01/2012 20:10:19
498 forum posts
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Kevin
More to the point what is your cylinder made of? Do you mean brass or is the piston gunmetal or bronze. The brasses that we normally use are not good bearing materials, you will find that a brass piston will wear quite quickly if given a reasonable amount of use. If your cylinder is of brass then you have no real option but to use soft packing or 'o' rings, piston rings will have a tendency to wear the bore as they will need to be made of a disimilar material (cast iron rings in a cast iron cylinder are O.K.) brass/bronze/gunmetal rings in a cylinder of the same material will have a propensity to pick up. Personaly I would use graphited yarn packing.
JasonB27/01/2012 20:15:18
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25215 forum posts
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Couple of oil grooves should be enough, thats what the original has.
 
J
Kevin Bennett27/01/2012 20:19:20
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193 forum posts
56 photos
hi Dusty the cylinder is fine grain cast-iron also i have not made the piston yet
 
TY Kevin
Stub Mandrel27/01/2012 20:44:54
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Kevin - I used graphited yarn for mine, but since then I have used 'nitrile' o-rings. Brass or gunmetal pistons in cast iron cylinders.
 
Neil
Alan Reed 128/01/2012 09:35:32
10 forum posts
My 10v works well with the oil grooves as per the Stuart drawing.
Dusty29/01/2012 09:59:44
498 forum posts
9 photos
Kevin
If you have a nice cast iron cylinder I would use a cast iron piston and as a couple of the guys have said oil grooves should be enough. Make the piston slightly on the stiff side in the cylinder bore, then polish the piston with some fine wet and dry say 800 grit
back this with a 6"rule to keep it flat (you don't want a convex piston) when it is a nice sliding fit pat yourself on the back. Take care with the wet'n'dry it is amazing how fast you can remove a couple of thou.

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