Bacchi leak repair - Page 4

by **zix** on Thu Sep 08, 2011 4:08 am

And did it start working again? If not, did you give up and put it away or did you find and fix the problem?

Opened the other Bacchi box just now. Flat bottom, much better fit in the outer bore - eve though metal on metal can be heard when pushing the piston. It doesn't "stick", either, perhaps a slight resistance just at the start but nothing like the first one.

by **orphanespresso** on Thu Sep 08, 2011 5:17 am

I have been working with a couple of Bacchi owners with this bottom leak issue that pops up from time to time and I think that the solution involves a number of factors....I have personally become so frustrated with the Bacchi at times as to rend my beard but it is mostly my fault, as when setting up the steam regulator valve and servicing a machine I tend to change too many things at once and then have to work backwards to sort it all out. The first thing I would do is to set the center valve end adjustment at 3.25 turns out from seated and assume that this is approximately correct, within 30 seconds on whistle depending on the heat source. Next, insert the lower piston section onto the base, hold the base in one hand and the piston in the other and try to "mate" the two parts...wiggle and joggle the two while turning the piston part around. There seems to be one spot in the rotation where there is very little wobble on the two mating surfaces. When you find this best fit, mark the back of the piston section with a scribe at the center of the bottom plate and always assemble the two components on this alignment.
I have planed the bottom mating surface flat with wet abrasive but still found that finding the best fit of the two parts is possibly more important than the flattening of the surface. This requires a session of intense observation of these two parts but time well spent. I have also inserted a small washer in the top of the cap, where the threaded rod tightens against the body and find that this prevents overtightening...it gives a bit more thread to work with and allows one to feel the point of correct compression of the machine elements.
Another thing that can happen when repeatedly heating the machine with plain water is this.....you place the machine on the heat with water in the bottom and the cylinder and watch the clock attempting to get that valve set correctly. When there is no hiss or whistle at 6 or 7 minutes you take the machine and open the valve with a great burst of steam and hot water indicating that it is under pressure, but no whistle...then cool it down under running water. This causes the whistle valve to pop back sharply, often with a little back whistle, like when you whistle by sucking in air rather than blowing out. This rapid cooling in cold water can actually jam the valve open, preventing it from the hiss and whistle function as designed. I do not think that rapid cooling harms the metal but can jam the valve, making the whole thing even more difficult to sort out.

by **Ian_G** on Thu Sep 08, 2011 7:13 am

zix wrote:First test with Molykote 111 done. It still leaks from the bottom, but we will give it two or three sessions before taking it apart again. We applied about 30 mm of 111 on the large bore and 20 on the small one, so double the quantities of what was recommended here earlier.
It works better now, but I guess it is still a bit stuck in the bottom,

Reading this, my overwhelming feeling is that you have used waaaay too much Molykote. It needs to be an almost invisible film that is applied. You will know from using the stuff that it is very sticky and if you apply too much it will act a bit like glue, especially at the bottom. My suggestion would be to wash it all off and start again using it very sparingly. When I lubed each face I used a bit of Molykote roughly the size of my little finger nail on each face. I then dotted the lube at evenly spaced intervals around the circumference. Then using my finger tip spread the dots to cover the entire surface. It should feel as if it's barely there.
Then I depressed the piston half a dozen times and then, using a paper towel, wiped around the base of the inside face of the outer housing, to a depth of about 10mm and depressed the piston another half dozen times.

by **zix** on Thu Sep 08, 2011 7:46 am

Ian, it might well be so.
I have been taking away the excess grease as you describe, from several places, and surmised that if there is no more excess grease coming out, what is left inside is needed. But who knows, silicon is known to creep around a lot, so perhaps there is still lots of it left. I put a lot in there because of the less than perfect fitting - too much play in several places, metal touching metal in others. This is a very very viscous grease, but it still can't quite suspend the parts so there is a distance between them along the entire wall. This gives me exactly what I don't want: a sticky and uneven movement of the outer bore.

OE: thanks a lot for that whistle valve tip - perhaps that is what has happened to us also. I did cool the machine down quickly a couple of times once it started giving us problems.

It is comforting to hear that even a seasoned technician like yourself gets frustrated with things like this. I find the Bacchi fascinating, but much like the print press I was running many years ago, fault finding and fixing follows a very different logic than programming does. Even though the machine is small, all parts and processes are interdependent. I am used to being able to cut up the problem in many parts, fixing each and then the entire kaboodle works. Not the same way here...

Is it possible to unjam the valves by unscrewing those set screws and unjamming the valves with a wood toothpick or something like that? If my guessing is correct, the whistle valve and the hiss valve ought to have their reference (closed) position towards the inside, since the steam pressure must push them out to open them.
Getting at them from the inside of the valve seems a bit more difficult...

I have also seen that sometimes it seems less leaky depending on how I turn the main part when I put it on the bottom part. Will try finding the best placement also, and then report back.

by **zix** on Fri Sep 09, 2011 5:43 pm

Followed your advice today and tried to find the best fit for the bottom and the main "boiler", twisting it around and wiggling, checking fit a.s.o. It is very obvious once you start looking that this is not the same tight fit it used to be. One position was better than the others, and I was able to push it down over the bottom part far enough for the gasket to make contact and seal the bottom boiler. It still creaks and clicks when warming up, so I need to be careful not to over tighten it before it starts heating up.

I have a trumpet at home which has an oval valve ever since my (then young) son did a "timmmbeeeeer" lumberjack imitation, with the trumpet symbolising the tree - falling on the floor from on top of a 'speaker. That valve behaves just like these two parts. At a certain degree of rotation, the two parts just about fit together, but at all others, they don't, which means the valve piston can't be slid into place unless I am in "the zone".

And it makes coffee again. And it hisses and whistles! Granted, it does an annoying creaking sound when the piston is pushing up the coffee, but with any luck that will disappear. If not I'll try rotating the crown to the other two positions and see if that helps...

Thanks all for helping us get this far. The Bacchi needed both grease and a re-aligning, and a bit of love to start working again. We'll see if things improve with a gas heater - I have gotten hold of my first one but haven't tried it yet.

by **zix** on Sun Sep 11, 2011 3:55 pm

Did a first test with gas.
I already had a Trangia camping/hiking stove, so I upgraded it with a gas burner (Trangia is popular in Sweden, don't know if anybody except Swedes know about it, but it is like Primus or Coleman or the like. Base model of Trangia uses ethanol, but is upgradeable to gas).
First try: it started whistling in around 3 minutes. Scary efficient! The Trangia stove when mounted works like a chimney, and the burner is mounted in the middle of it. I put the Bacchi where the pot usually sits (without that lid/frying pan in the linked image), and heat started streaming along the walls. A good thing, but I was worried that the plastic knob would be damaged, so the second time I protected it with a piece of iron as deflector.

Second try: a bit slow. 8 minutes. Too little heat to begin with, and I tried to compensate by putting it in turbo heating at the end. After pouring the coffee and coming back I saw that the aluminium plate I had used under the Bacchi to support it had melted... oops.
Thin aluminium... no harm done to the Bacchi though, this was the new one and it was as flat-bottomed afterwards as it had been before. Perfect fit with all parts on this Bacchi.
Probably better to put it a little bit further up next time. With steel supports, not aluminium...

Would have preferred if the effect regulator for the burner was easier to fine-tune, but I guess I should have bought something else to get more control. Didn't want to buy one of those larger gas stoves, not just yet. At least it is fast, and more than adequate for the Bacchi.

So is gas better for the Bacchi than electric heater? Yes, yes, yes. You get more heat streaming up along the outer walls, Trangia or no. I definitely think that is better for the general heat dispersion. Don't think we will need to experiment with an external heat gun to get the coffee hot enough now. Not as long as we use gas heater. In addition to that, you won't end up in the vicious circle of applying ever more intensive heat to an ever decreasing point of contact if the bottom does get warped.

by **prijicrw** on Thu Sep 15, 2011 2:05 pm

Hi Doug. Thanks for this posting! I would really like to order one of these softer silicone rings. Can you provide precise specs? I found several sites which seem to have countless kinds of o-rings - or if I can, I would get it from you as well.

Unfortunately, the larger o-ring you sent me makes the leak worse - even after many trial & errors. So please do let me know about the silicone o-ring. Thanks very much! ~Ryan

by **zix** on Thu Sep 15, 2011 5:21 pm

Extra support mod finished. Took six of those iron angles that sit in computer chassis, protecting the mounting holes for extra graphics card and such. The computer was going anyways, so this was true surplus material, and free.
Drilled, bent and screwed them together and made sort of an outline "T" shape that goes on top of the usual pot holder angles. Other shapes would have worked just as well I guess. This was stable enough to hold the Bacchi and gives it an extra 2cm of distance from the burner. No melted metal. 5 minutes total heating time, lots of headroom in this process, and this heating method is definitely better for the Bacchi, so again no competition, gas FTW.
Now that the stand works, we just need to find the best heating place - preferably somewhere discrete...
Sorry for bugging you about this, I just don't know where else to jot it down.

by **prijicrw** on Fri Sep 16, 2011 12:38 pm

I am just curious - in what countries is the Bacchi under any warranty? I have now been very frustrated with my only source of coffee for 6 weeks = : ( !!!!!!

by **prijicrw** on Mon Sep 19, 2011 10:56 am

orphanespresso wrote:Having recently received a Bacchi which the owner had COMPLETELY melted down, and I mean melted down, and on the first session at that...seems some distraction caused the machine to sit on the hod for an interminable amount of time. The result was that all of the plastic parts liquefied and reset...the teflon disc atop the piston was black and had clogged the ports in the filter basket carrier and the dispersion screen block had melted as well, so you can see that this machine took some extreme heat...more than normal use. Interestingly, the two U cup viton seals were still supple and not distorted and all the viton o rings were fine and did not need replacing. The silicone seals in the 3 valves were fouled a bit but no damage here either. The machine came through amazingly well...but for the replacement or repair of the plastic parts (2) and not surprisingly a warped bottom plate.
Though the plate is a replaceable part and is simple to replace, held in place with two cap bolts, I spent 2 frustrating days trying to address this warped bottom issue. First by changing the original bottom o ring with a fatter ring of the same diameter. This was a logical step but did not work, and the reason was not apparent. Then I planed the top surface of the bottom plate (the surface that meets the sealing ring) with 400 grit wet sandpaper on a flat surface. One can see the sanding marks on the two outer edges at the assembly bolt ears on the plate, and slowly sanded until the paper was scoring the ring all around. I installed the fat ring again thinking that this would surely fix it and still it leaked. Much puzzlement, heating and cooling and trying again and again. I installed a washer on the top of the machine cap where the assembly knob/bolt strikes the cap to allow even MORE tightening and this of course did not seem a good idea since I think that overtightening to stop that sputtering leak at the bottom plate is part of what causes it to warp in the first place. Still no joy.
Then I really looked at the two sides of the sealing surfaces and thought about it, examined the apparently too thin original o ring, and thought some more and made a few more runs to realize the following:
Even with the surface of the bottom plate (upper) planed completely flat and the fat ring, what was happening is that the sides of the plate compress the ring more than the middle of the plate....the parts next to the side rods squeeze the ring almost flat but the center parts (90 degrees from the side rods) do not compress as much.....the design is such that the entire metal surface of the seal side of the junction must meet on face to give an even compression of the seal and an even junction of the bottom plate and the piston assembly. So the problem is two fold...fist, the plate can warp, even slightly from heat followed by over tightening resulting in a small leak and more overtightening.
My observation is that the viton o ring is fairly hard durometer and the surface can become ever so slightly flat, not a lot of sponginess in the ring, and the seal is very subtle (examine the tiny amount that the ring sticks up above the metal surface). I installed an orange silicone ring (durometer 50, medium hard) of the same diameter as the viton original (70 durometer hard), and with the verified flat planed surface combined with the softer seal (.2mm larger diameter) I solved the leak.
This is repeatable and I did the same thing with a second machine directly as a bona fide fix of this problem.
So try to plane it down so it is flat (test on a verified flat surface) and install the original thin o ring with lube to see what happens. The fat ring is not the answer, unless it is both fat AND soft, which I have yet to try, not having that ring to experiment with.

Hi Doug. Thanks for this posting! I would really like to order one of these softer silicone rings. Can you provide precise specs? I found several sites which seem to have countless kinds of o-rings - or if I can, I would get it from you as well.

Unfortunately, the larger o-ring you sent me makes the leak worse - even after many trial & errors. So please do let me know about the silicone o-ring. Thanks very much! ~Ryan


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