I've ordered up a BSC thread repair kit from the UK (only one I could find with shorter thread inserts ... most were 1.5D ... but found one with 11mm inserts).
Given its not a through hole, I'm a little concerned the intermediate tap may not cut sufficient threads at the botton of the hole for the insert - but will wait and see. There does appear to be a supplier of a bottoming tap for these inserts in Australia (https://www.powercoil.com.au/product...176&catId=1250) so should be able to get my hands on one if necessary.
I've also ordered a 7/16 BSB Tap and Die set. I'm thinking I'll try to 'build up' the threaded section of the damaged brass valve with jb weld and then cut a new thread with the die. This will also give me the ability to make plugs if needed given these don't seem to be an off the shelf item.
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FYI Guys - if you want to go down the British threads rabbit hole, this site has quite good reference information on the common and obscure threads.
https://britishfasteners.com/help.html
PS. All this reminds me of when I was working with another company on a design project which had to incorporate a component made in the UK. The company was using a German mechanical engineer for their part of the design, and he had a comprehensive brain-fart when he first saw the threads the UK company had used - a 1 1/8" x 40 TPI bastardised Model Engineering thread, and a number 2 0.185" x 33.36 TPI British Association thread. He must have spent his whole life with metric thread forms, and this really offended his sensibilities! He rang me up specially to unload about the stupidity of British thread forms. I was tempted to mention that they won the war using their threads - twice, but I felt sorry for the poor bugger because British threads are weird!!Last edited by Stavros; 23 October 2022, 12:26 PM.
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Something to consider is that there is also a British Standard Cycle, (BSC), thread which is available in 7/16" x 26 TPI. It has a 60 degrees thread profile, not 55 degrees, but that shouldn't be an issue for you. Being somewhat more common, you should be able to source the thread insert kits easier and cheaper. I see that the helicoil kits with 14 inserts are available from A B Tools via Amazon or eBay for around $160, making this a reasonable option.
If you are lucky, you may also be able to find a good bike repair shop which has the insets and would be able to fit one for you.
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Thanks Stavros. There was a face seal I think ... wound hemp. I'm now using a viton o-ring.Originally posted by Stavros View PostOne question though, how was the original fitting sealed? Was it by the thread itself, or some sort of face seal between the fitting and group body? (Thread Sealing Methods).
I too would prefer to retain the original thread - especially in the context of me now having a couple of these 2-group machines the same - and keen to maintain them standard. I'm just not sure whats possible and what the expense might be to creata a new needle valve fitting.
Another challenge is actually sourcing the 7/16 BSB thread insert. It looks like I can buy a kit with drill, tap and inserts in Germany for some 260 Euros but they will not post to Australia! I've also found the inserts in packs of 100 in the UK for 80 odd pound - but nil stock, I'm not sure they'll deliver to Australia. I cannot find any info on what thread would need to be cut to accomodate the insert either.
After writing the post this afternoon, I went and swapped some of the valves between groups. I was able to get the valve with the least threads to 'hold' in the group with the best threads. I was even able to get the valve with the best threads to 'hold' in the group I'd run the M11 tap through - but the fit is very loose and far from ideal. All untested under pressure.
Perhaps its time for me to buy a lathe and a mill and start learning some new skills? No room for either unfortunately.
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Stripped threads can be a pain, but as you note there are a number of ways to fix the problem, especially when you are lucky enough to have a thick casting to work with like that group.
If it was a plumbing fitting, with BSP or NPT threads, my first thought is always to drill and tap the next size thread into the body and screw a bigger fitting into it. Sometimes you can 'jump' between different threads forms and standards, (metric, BSF, brass, parallel BSP, etc), so that you are only enlarging the female thread by the minimum amount, provided you can source a suitable male fitting or part.
With something specialised like this, with a 26 TPI brass thread and a complicated little flow/needle valve, it would make sense to try and retain the original thread size and form by use of a thread insert. This would depend upon how bad the male thread is on the flow valve, or if you could find another one somewhere. One day a new owner will curse you if there is some unusual or unobtainable thread/fitting in it.
As a retired machinist, if it was a job for myself, (and no one else would see it), I would use your 1/2" BSB tap, and then turn up a bastard flow fitting to suit. This is cost effective for me, as I'm not charging myself $$$, and I like machining brass. The only thing that could make the job nicer would be if the thread pitch was divisible by '4'.
If the space was available, it may also be possible to turn up some sort of a thick-walled bush, with the correct 7/16" 26 TPI brass thread on the inside, and a suitable sized thread on the outside. This group would need to be tapped out to suit, and the bush screwed and loctited into the group. This is not an attractive option but can sometimes get you out of trouble.
An even less attractive option would be to have the stripped thread in the group braised up, and then re drill and tap the correct size thread in it. With this, there is a substantial risk of the heat distorting the group, making the all-important main bore out of round.
One question though, how was the original fitting sealed? Was it by the thread itself, or some sort of face seal between the fitting and group body? (Thread Sealing Methods).
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Calling for advice from hobby or professional machinists ....
The inlet flow control on one of my groups requires repair. The threads on the valve and in the group are all stripped out and its not possible to get it to seal.
In trying to work out its thread, I stupidly ran a M11*1.0 tap into the group. Doing so served no purpose ... I wish I'd not done it - although in the end it probably matters little.
Having spent a bit more time investigating, I think the thread was likely 7/16 British Standard Brass 26tpi 55o Whitworth.
I'd like to be able to get the group functioning again.
1. How important is it to be able to control the flow?
An option is the cut a new, larger thread (perhaps 1/2" BSB) into the group, and just insert a plug that does not interfer at all with the water gallery. Essentially allowing 'full flow'. There is plenty of material to allow this.
2. Could a thread inset be used in the group?
I've managed to locate on the web a couple of UK/German sellers or 7/16 BSB thread inserts. While expensive, perhaps this opens up the possibility of restoring the group to its original specifications. The upside would be that I'd acquite the inserts and tooling to repair any of the other 3 groups I have should they also suffer the same fate.
3. Is there any other option to repair the group that I haven't thought of?
Now to the valve.
Given parts are unobtanium, the only option to return the valve to spec is to get a machinist to remanufacture the part of the valve that has lost its threads (it would be turned out of brass 3/4 hex bar). Quite a fiddly and as such time consuming job I expect (there is 1 male and 2 female threads on each part) and as I don't have a lathe or any machining skills ... I'd have to pay. The upside of this would be the ability to do a run of them ... as I have 4 of these groups and at least one more of the valves is already damanged (its untested but I think functional) - new valves all round would be nice.
4. Is there anything that would do the same job available off the shelf? Photos of the valve below.
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Hi Mark
I haven't been able to find group seals that match exactly, and am away from home ATM so can't look at what I did end up using which has proved 'good enough'. I think it was a seal to suit rancilio
Re steam and water, I used good quality regular tap washers .... the brass ones.
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I've just been delivered an almost identical Boema lever machine. The boiler on this one is dated 1982.
I'm hoping you can help me with some issues I'm finding in determining parts. I've been looking at CoffeeParts web site and others.
Questions:
1) The Group seals I taken out appear to be 74x57x7. The Shower screen is 57mm OD, yet the CoffeeParts group seal 700501 is specified at 66x56x6. What group seal size is your/What seal do I need?
2) I cannot find replacement washers for the water and steam valve washers. They look very similar to a standard household tap washer, 17mm diameter. The stem is about 5mm diameter. Do you know where I'll find suitable replacements?
Thanks in advance, Mark
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Well, I'm up and running. The pipe bender I bought was rubbish for bending 3/8 copper ... so other than one new pipe, I've just re-installed the old (hard) pipe, and still have a couple of minor leaks from compression fittings which I think would be easily sorted by annealing the copper pipe ... but there is espresso to make ... so that can wait. I'm considering just lashing out and buying a dedicated 3/8 bender ... which might then allow me to make some new stainless steam arms too.
My inlet tap has a drip ... waiting for the viton o-ring kit to arrive before I tackle that. Nothing the occasional wipe with a cloth doesn't fix.
All the main things ... boiler gasket, element gasket, water inlet gasket, group flange gaskets are great. Not a drip.
Unfortunately the old float valve controlling water inlet hasn't worked, and I'm not pulling the boiler apart to find out why for now ..... so am controlling water level in boiler manually ... which I find is actually no big deal ... I only need to do it once a day at most.
The groups/levers are working beautifully. Pulling shots without the noise of a pump really is nice.
I've set the pressurestat at 1.2bar and can walk up and pull a shot without any 'flush'.
I've used the old toothpick trick to block some of the 5 holes in the steam tip to make steaming small milk volumes easier ... and am now getting good textured milk too.
Initial impressions are it is very forgiving ... shot consistency is high, with the exception of when the dose in the basket is too small.
I now need to turn my mind back to roasting so I've got some fresh beans to work with (its been ALDI beans to date), and see what this baby can really do.
Shout out to kofekitt for his assistance with the gasket material and other advice.Last edited by towe0609; 5 May 2019, 11:04 PM.
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Best to keep the p/stat mounted away from the boiler so as to avoid accelerated degradation of the electrical and plastic components of the device...
Mal.
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Cut a boiler gasket using the new gasket cutter which worked well. Waiting for stainless fasteners, but put it together with mild steel bolts as a test run ... lookin' good!
Any reason not to mount the new pressurestat directly to the boiler? Previously it was mounted to the frame via copper pipe with compression fittings etc ... but I selected a pressurestat with the right sized fitting so fitting directly to the boiler was an option. I can also make up a pipe to mount it away from the boiler if there is a reason to do so.
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The holes in the piston are to allow water flow through and too 'energise' the seals (make the seal edge flare out and work better)
Are the shower screens the toothed variety? If you push in the middle (with the piston raised), they pop into a concave shape and are easy to remove. Same for installing - pop them into concave shape, hold in position, and poke a wooden dowel down the bore to pop back into convex shape
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Thanks ... I'll 'pack' the space with a washer ... but I doubt the piston will turn on the shaft anyway with the big spring holding it firmly in place.Originally posted by kofekitt View PostBottom of piston should be approx flush with bottom of bore, have a pic?
I've already installed the shower screens, and at $20 a pop I don't want to risk damaging it trying to remove ... so no ability to check how flush with bottom of bore unfortunately. Might have to cross my fingers on that one.
I should have studied it more closely, but when the bore is up (ie. spring compressed) fully, I assume it is above the water inlet point to the chamber. But what are the small holes in the base of the piston for? Are they just to slow the pace of water pushing against the seals when the piston is released? Or do they have some function associated with the inlet?
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