Part built Allchin 1.5 inch

[Paul KempParticipant @paulkemp46892]

Derek,

Any chance you can post a picture or two of what you have and maybe a shot of the relevant part of the drawing? I am not familiar with the Alchin design. I would assume the "poppets'" have a stem with reliefs machine in to allow the passage of steam and guide the valve onto the seat but maybe not in your case!

Paul.

[derek blakeParticipant @derekblake72550]

Hi Paul, pictures added.

the poppers are a loose fit in the bores as the drawing to me wasn’t very clear.

id like some made for me but in these dangerous times it’s not easy to find a machinist rightly so of course.

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

I’ve tried grinding the poppets in, even if I tighten the spring it still leaks so clearly something I’ve done wrong.

[MichaelRParticipant @michaelr]

To work correctly the ends of the pivot pins on the lever arm should locate slightly below the valve seating, and the valve seating face not too wide,

MichaelR

Edited By MichaelR on 10/04/2020 19:28:26

[derek blakeParticipant @derekblake72550]

Hi Micheal

Do you mean the tips of the lever should be deep inside the poppets and not slightly balanced on top?

should I drill down into the poppets so they sit inside.

Thanks for the help

[derek blakeParticipant @derekblake72550]

I’m pretty sure the tips were further in as requested, I actually filled the holes with solder to higher the recess up.

so I think if I drill back down they still won’t seal.

🤷‍♂️

[MichaelRParticipant @michaelr]

Posted by derek blake on 10/04/2020 19:46:08:

Hi Micheal

Do you mean the tips of the lever should be deep inside the poppets and not slightly balanced on top?

should I drill down into the poppets so they sit inside.

Thanks for the help

Yes the tips should be drilled into the poppets so that they are slightly below the valve seating (As in the drawing above) if they are just balanced on top the lever can flop about.

Michaelr

[derek blakeParticipant @derekblake72550]

Hi Micheal

I’m not sure if you know the Allchin safety valve, but regarding the wings on the poppets should these be a good fit in the bores?

i made mine what I thought was correct but there very sloppy in the bores, no matter how many times I look at the drawing or read the book I can’t understand the fit.

i could do with a cut away drawing that shows how the poppets/cones fit down the bores.

but unfortunately I think the poppets have now gone past use from me messing around with them and as such I’d like to find to machining company to make the safety valve safe!

Regards Derek

[Paul KempParticipant @paulkemp46892]

Derek,

As Micheal says the point of effort for the spring bar needs to be below the line of contact with the valve and seat. One of the points on the bar as indicated in Micheals drawing also needs to pivot. You will not find a pair of these valves that both lift at exactly the same time so small degree of articulation is required. The set up shown is similar if not identical to a set from a Burrel I repaired for a friend. Adjustment was a nightmare as the adjusting nut was inside the steam cavity. I ended up making a false housing for the valve assembly to bolt on to and set them up on air for the lift pressure. Air does not behave the same as steam but in terms of the actual pressure to get them to lift is close enough, it's the re seating that will not be the same as the air does not have the expansive property of steam. You say the fit of the valves in the body is "loose" what does loose actually mean? A couple of thou clearance, 5 thou or 20 thou? They should not be a tight or even a close sliding fit at normal temperature as you need to allow for some expansion, the last thing you want is for them to bind when they get hot and jam shut! Conversely they don't want to be so slack that you can throw them in from the other side of the room? Loose is a relative term here!

As Micheal also says the width of the seat wants to be fairly narrow I am not sure of the relative size of these parts but I would say 25thou contact would be more than plenty. If the body were machined to a sharp corner and then lapped in with fine time saver the resulting bevel of the seat should be plenty.

I would suggest for a start you make a dummy housing with an air connection, get a bit of weight on the spring (having lowered the point of contact for the bar by removing the solder) and see what happens and at what point they lift -! You need a decent gauge in the system! If it's any consolation this type of valve in miniature are really hard to set up and get working right, that's why lots of people hide a pop type valve inside a dummy representation! Also at the moment if they leak like a sieve they are as safe as you can be because you will never build up any pressure in your boiler under steam!

I am afraid this is a case of patience and perseverance and unlikely to be solved purely by having two new valves made. You will get there.

Paul.

[derek blakeParticipant @derekblake72550]

Hi Paul

many thanks for your help yet again, the valves are under size in the bores but I will try and work out by how much.

its possible I may need to start fresh with a whole new safety valve etc, this is an area I’d rather farm out as safety is my first priority and it’s not something an inexperienced builder like me should risk.

what with how the world is there obviously far more important things going on than an engine but I will try again.

i can blank the area off for now to run on air as I can keep the air regulated on the compressor but I would really like to get the valve sorted eventually as I hate being beaten.

kind regards

Derek

Edited By derek blake on 11/04/2020 00:39:03

[Paul KempParticipant @paulkemp46892]

Derek,

That's the spirit! Measuring the valves will be difficult as they have three flutes, easiest way would probably be taking a first guess undersize and drinking a hole in a piece of plate, then slowly keep opening it out. Can't remember if you have a lathe but if you do then bore out in small steps until the valve goes in and then you can measure the hole – will be close enough. Can you post a couple more pictures of the body and the underside showing how the spring is adjusted?

Paul.

[derek blakeParticipant @derekblake72550]

Hi Paul

interestingly I just looked up the bores in the sun and you can see daylight around the valves so there clearly no where near seating correctly 🤔

[derek blakeParticipant @derekblake72550]

Hi

May I ask, im setting up the reversing lever but I’d like to ask should the die block be setup to the extreme on the expansion link or a certain amount from the ends.

at the moment I have the die block going further one way than the other but it would be good to know if I should be leaving a gap at the ends.

if I shouldn’t then I’ve made the push rod too short 😳

[Paul KempParticipant @paulkemp46892]

Derek,

There should be a gap between the die block and the end of the link. Has to be to allow for link slip. Usual for the centre of the die block pin to coincide with the centres of the valve rod pins which means the valve travel is going to be close to the eccentric throw. God place to start a check is mid gear on the reverser has the die block in the centre of the link if the drawings are good!

Paul.

[derek blakeParticipant @derekblake72550]

Hi Paul

thank you for the quick response, well that’s good news then to be honest.

i will check the pin location in the morning then, it’s possible mine is still a bit too far from the ends but this is only since I connected the push rod.

but I shall double check if I have the same amount of gap in forward and reverse,

Derek

[derek blakeParticipant @derekblake72550]

Hi, could slight play in the crankshaft bearings cause a knock?

[Paul KempParticipant @paulkemp46892]

Derek,

It could but more likely to be large or small end bearings. If it is the crank if you put your hand on the flywheel it is likely to damp any noise from main bearings but potentially amplify large or small end. The possibility is if you haven't got the piston positioned right it could be clouting either front or rear covers. When I shimmed the large end on my Ruston I didn't think about that and the resultant noise from the piston coming up against the rear cover was a devil to find!

Paul.

[derek blakeParticipant @derekblake72550]

Thanks Paul, I actually disconnected the piston and you can hear a quiet knock when you swing the crank back and fourth,

i had the eccentrics connected at the time, I’ve listened to other Allchins on YouTube and some if not all have the same knocking sound, so maybe it’s normal on this small engine.

my knock is pretty quiet compared to some.

regards,

Del

[derek blakeParticipant @derekblake72550]

So the trials and tribulations off engines, slight knock in reverse but singer sewing machine in forward, very weird.

ive changed the bearings on the crank shaft, checked big and a replaced small end, so give up at the moment.

its a new thing so I guess something has changed 😔

[derek blakeParticipant @derekblake72550]

Pulling my head out with the final stages of the engine, knocking sounds seems to be bearings, however even after replacing the knock appears again, there seems to be a tiny wobble on crank that unevenly wears the bearings.

the crank shaft is something I can’t fix so looks like the slight knock is something I’m going to have too live with.

shame because I wanted it to run smooth, I had other parts that required work such as crank alignment and loose cotter pin all fixed but bearing wear pretty quick after making new ones.

i cant keep chasing my tail and going in circles so I think that’s the best I can have.

[derek blakeParticipant @derekblake72550]

Maybe someone clever has an idea of a fix, I think the crank has a slight wobble so the bearing wears ever so slightly and I can pull the crank up and down causing a knocking sound.

if I replace the bearing I get the same result after a while of running, any suggestions 🙏

kind regards,

Del

[derek blakeParticipant @derekblake72550]

As it’s far away from the heat, could I use PTFE plastic bearings inside the brass’s so not to have metal on metal and possibly remove the knock?

[Paul KempParticipant @paulkemp46892]

Derek,

PTFE is OK with heat, I use it as valve liners for water gauges and drain cocks etc, swells when it gets hot though and goes brittle over time. I guess the loads on a 1.5" scale are fairly light but even so I think you might be pushing it a bit. Given you haven't steamed it but are test running on air I am surprised the bearings are wearing that quickly, are you using brass or bronze? What is the nature of the wobble on the crank? Is it built up or machined from one piece? Can you not set it up true one end and then lightly skin the other to square it up and use an undersized split bearing where you have skimmed it? Afraid I am not familiar with the design so not easy to give good advice!

Paul.

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