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PYRTE Build

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Ken Ratcliffe30/10/2020 14:04:05
24 forum posts
2 photos

All,

Any help welcomed ! I have posted previously about building PYRTE. I have my boiler all sealed up and holding pressure (last post !) and all the steam piping to the engine and out to the exhaust tight. When I pressure it up and open up the steam to the timing valve, all that happens is a lot of steam comes out of the exhaust and there is no feeling of the piston wanting to move on its own as I spin the flywheel. I am fairly sure the valve timing is OK - if not perfect not that far off.

I am wondering if my piston isn't sealing well enough, i.e. steam is passing the rings and going to the exhaust irrespective of where the valve cover is ? The rings look well seated and the inside of the piston is smooth, but when I pressure up with air (using a footpump) some does pass the rings. Being as this is my first steam build, I am not sure what is acceptable, i.e. should the rings pretty much be "air tight", or is some leakage OK........

Sorry if this is a bit vague, but just hoped someone may be able to give some guidance (as you all have with my previous novice questions)

Ken

Jim Nic30/10/2020 15:20:16
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279 forum posts
164 photos

It sounds as if the valve (it is a slide valve, I take it) is not seating on the port face thus allowing the steam to avoid the cylinder completely and just go direct from the valve chest out of the exhaust port. Particularly as I get the impression that here is no restriction or force preventing you turning the flywheel even though there is steam pressure in the engine.

Is there something holding the valve off?

Jim

Ken Ratcliffe30/10/2020 15:31:35
24 forum posts
2 photos

Hi Jim,

Glad you said that, it was my first thought, just because so much steam was just heading straight out the exhaust. I have skimmed some of the chest walls to make sure the valve was in good contact with the block.....so there doesn't seem to be a reason it held off the face and both are smooth faces, but that is not to say there isn't a reason.

I will have another play with the valve seating tonight when I get back from work as a starting place !

It is a side valve and yep, the flywheel turns easily BTW.

Ken

Jim Nic30/10/2020 16:21:34
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279 forum posts
164 photos

I am assuming that the valve is similar to this one from a Stuart stationery engine with the rod going front to back between the castellations across the valve and is threaded in the cross piece which goes from left to right between the castellations.

vscn1066.jpg

It should not be necessary to skim the valve chest wall as long as the valve operating rod and cross piece are both free in the valve itself.

Not wishing to tell you something you are well aware of so please forgive me if you know this: the valve should be free to float up and down to a small degree in relation to the port face to ensure good contact, it is the steam pressure in the valve chest that holds it down.

I have read a thread in another place where the modeller ended up fitting a spring between the top of the valve and the chest cover to ensure good valve face contact but I would say that should not really be necessary.

HTH

Jim

Ken Ratcliffe31/10/2020 11:08:35
24 forum posts
2 photos

Hi Jim,

Thanks again. I put a small bend in the pushrod inside the chest, so it is a little bit closer to the block, made sure it has some play...….and yep, I now have a working steam engine !

Still a lot to do, but a pressure tight boiler and a working engine means I am on the home straight !

Ken

Jim Nic31/10/2020 12:31:29
avatar
279 forum posts
164 photos

Good to hear.

Jim

Rolf Gratze01/11/2020 16:42:08
3 forum posts

Hello everybody,

For a couple of months I've been trying to build Pyrte. I'm from Germany, so I'm struggling hard to understand all the instructions, given in the book.

I got as far as building the drive and now I'm facing some problems referring to measurements.

firstly: the centre of the driving pin is said to be 1 and 7/8 inches from the centre of the rear wheel. But when building the inner water pump drive and the large cogs, I'm advised to put the holes for the driving pin tubes 1 inch off the centre. So what is correct ??

Secondly: the driving pin tube needs a boring of 3/8 inch to be fit for the driving pin of 3/8 inch. Later on, when the making of the driving pin is described, the diameter of the driving pin in only 1/4 inch, which would result in too much space between the pin and the inner diameter of the driving pin tube, I think.

Could anybody please help me in solving these problems ??

Thank you very much

Rolf

Ken Ratcliffe02/11/2020 14:23:05
24 forum posts
2 photos

Hi Rolf,

I haven't got to the drivetrain yet, so can't help on your specific questions. However, I am English, have a couple of degrees - and at times find the book difficult to follow ! Throughout there are errors, notably in the early parts where the metric and imperial don't match. It keeps you on your toes though, doesn't it !

Ken

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