Some La Pavoni lever machines have the group attached to the boiler with M6 bolts that have only 12mm of thread. The threads on the boiler are in brass. The flange on the group is 6mm thick, that leaves only 6mm, perhaps a bit less, thread holding the group onto the boiler. A standard rule of thumb is that threads in brass should be at least 1.5 times the diameter.

It seems to me that there is a serious safety issue here. If one or both of these bolts should strip whilst one was pulling a shot it would be a catastrophic failure, with water flash boiling and spraying all over the area (including the operator). This has serious injury potential.

Replacing the two bolts with M6 bolts that have 16mm thread should solve the problem. The replacements should be stainless. One could also replace them with threaded rods and put acorn (dome) nuts on them.

There is a special urgency to change bolts if one installed any kind of gasket other than the stock O ring, because that would reduce the thread length even more.

Good point.

It is very difficult to argue with a safety issue. Especially one which is so easily corrected.
I agree 100% with Robert's post.

A search on eBay for "M6 16mm Stainless" will turn up a supplier who will send you ten of the bolts suggested for under $5. This supplier also has 14mm, 18mm, and other thread lengths available at similar pricing.

Socket head bolts are another good solution which is certainly more elegant than hex heads, and just as functional. Good choice!

How many threads are the boiler threads deep ?

on My Mcal they are not deep enough for a bolt one step longer (next normal size)
i do plan on making a custom length

I have counted the number of engaged threads on the La Pavoni group to boiler bolts on my two machines. There seems slight variation amongst the four original bolts. One has 5, the other three have six. Considering the fact that they are in brass, and the fact that there is considerable force on them whilst a shot is being pulled, this seems inadequate. The design of this flange also makes the system into a sort of lever that amplifies the force felt by the bolt. With a 16mm bolt there will be about 10 engaged threads. In the long term frequent exposure of the brass to such forces has to result in its deformation.

When I was a graduate student years ago I was a teaching assistant in a chemistry laboratory course. There was an incident one day in which I was glad it was in the other graduate student's side of the laboratory! A student that was on the football team got sulphuric acid all over a young lady who was working next to him. He, wisely, put her under the safety shower and pulled the handle. He was a football player, and hence strong. He was so strong that he managed to pull the bolts from a flange fitting just like this from the reservoir! The young lady did not suffer chemical burns from the sulphuric acid, but she seemed to nearly be drowned from all the water that came rushing down on her! (There was also a flood! There was water everywhere.)

How deep is the threaded hole in the boiler ;o)how many times is it possible to turn the screw before it bottoms out , just so that nobody is trying to tighten a screw that is bottoming out ,

True there is big forces at play , the distance from center of the flange and down to the bottom of the flange(pivot point)
that was the short arm
the long arm is the distance from the back of the flange ,and to the end of the lever at horizontal

now we can calculate how great a force is trying to pull the two M6 bolts out of there threads

then we just have to look up how much a steel bolt in bras can handle to know if things are ok

Ok , i took a look at it
the flange is 40mm high , that means from the center to the bottom its 20mm
the distance from the flange to the end of the lever is 300mm

that gives a 1 to 15 ratio

for a normal pull we use about 13 kilo
a maniac might use 30 kilo ;o) the base would flex as hell

30 kilo x 15 =450 kilo of force that is trying to pull both M6 bolts out
thats 225 kilo per bolt
or 450 kilo /0,454(a pound )=991 pounds for both

I did find the torque for a 1/4 brass 28tpi bolt thats close to a M6 bolt
http://www.engineershandbook.com/Tables/torque3.htm

it gives a value of 77 inch pounds

on this page we can calculate how much clamp force EACH bolt has at the value
http://www.engineersedge.com/calculator ... e_calc.htm
i entered 77 for torque
and 0,236 for major diameter (6MM)

it gave a value of 1631 pounds of clamp force .......for each bolt
that gives a force of over 3262 pounds
so if a normal thread engagement is used , we for sure have enough

but what IS a normal thread engagement?

we can calculate the minimum here , BUT i cant find the value for brass

but normally one says 3 threads is enough for the same material (a M6 thread has a pitch of 1mm , so thats 3mm)

using a steel bolt and a deeper threaded brass hole , just let us use more torque (the bolt can handle it before the head twists of )

but the clamping force is enough even with a reduced thread if the numbers i did find are correct
http://www.engineersedge.com/calculator ... gement.htm

I wouldent worry using the machine as is
but if i had it taken apart , i would use the longest bolt i could fit (remember to check )

better have it ,,and not need it ,than need it ,,than not have it