H10 stuart Turner cylinder

[Paul Rogers 7Participant @paulrogers7]

Hi.could any one give me advice on what min and max clearance you would work to between piston and cylinder.on h10.do you have to allow for expansion.

Thanks paul.

[Paul Rogers 7Participant @paulrogers7]

Tolerance

[Neil WyattModerator @neilwyatt]

HI Paul, because it's a steam engine and usually not heavily loaded you can get away with a fairly easy fit, a thou is probably ideal, as much as a couple of thou/close running fit is fine, especially if you use packing or a nitrile o-ring. Andrew Smith's book on the 10V says 'aim for a close smooth fit'. You certainly don't need an airtight honed/lapped fit like a ringless IC engine. Expansion shouldn't be an issue as it's a CI piston in a CI bore.

Neil

[Paul Rogers 7Participant @paulrogers7]

Thanks.neil. I have a .002" clearance. I was a bit concerned .like you say it's not under a work load.the bore is not as good as I would like still my 1st attempt. The mistake was the side of the boreing tool rubbed slightly. Still see how it goes.i can allways get a cylinder casting from stuart Turner. If I am not happy with it.

Paul

[Mick B1Participant @mickb1]

I might well have had more than that on my 10V. I used graphite-greased string packing for piston seal, and it's worked fine on air for over 20 years now.

[JasonBModerator @jasonb]

For the beginner it's not a fit that they can easily measure and I don't usually bother to measure it even now preferring to test fit as I take the last few though off the piston.

If you do find things need reworking then I would suggest first honing the cylinder with a cheap brake hone so that you have a half decent surface to work with rather than getting a new cylinder.

Then make a new piston from brass as supplies or even aluminium as the lighter weight will help with smoother running. turn the piston but leave it say 5thou over size then mount onto the finished piston rod and set the rod running true which will probably mean in the 4-jaw or using a split bush unless you have very accurate 3-jaw or accurate collets. Now with a very sharp tool take 1 though cuts off the diameter of the piston trying it for fit in the cylinder after each cut making sure to test each end just incase you have a tapered bore.

Once it will enter one end attend to any taper by additional honing or lapping until the piston will slide freely in the open cylinder but if you hold with your left thumb over the ports and palm of your right hand covering the end of the ecylinder you should be able to feel the pressure/suction as the cylinder is slid up and down.

I would not fit packing or a ring, the oil grooves as per the drawing will be quite enough and if you are only making for display then the lack of ring friction will help with slow smooth running.

This is the sort of fit you should aim for, cylinder end cover is in place and I have my finger blocking the ports and the piston slowly drops as air escapes around it. I'll post another video later of the engine I'm working on at the moment showing it with covered and open ports.

[Paul Rogers 7Participant @paulrogers7]

Thank you all for the advice. Great point on honeing. All so graphite string,thanks for showing the video. I am picking up these tips .I find it pays just to take my time and if I get stuck shout for help.thanks again. 😊

Paul

[JasonBModerator @jasonb]

Paul, this is the engine I'm building at the moment. The cylinder cover is fitted to the bottom of the cylinder and closes that off though there is no gland packing or piston ring in place nor any oil to ease things or act as a seal. You can see the piston slowly drop as air escapes then I push it back up to the top and it starts to drop again. About half way down I push the valve (round in this case) out of the valve body which lets the air out and you can then see how freely the piston moves. If you look in the "workshop progress" thread you can see the engine which ran first time.

Only a digital calliper used for measurement to get rough size and final finish cuts used the cylinder as a gauge.

[Paul Rogers 7Participant @paulrogers7]

Hi.jason.thanks for all the info.that is some machining.i get there one day with practice. I am getting better by the day sercret is take my time reading the drawings slowly.

Paul

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