Londinium piston removal - Page 6

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OldNuc

Postby OldNuc » Feb 23, 2019, 9:10 pm

Switch to the silicone seals and it may be just fine. Right now you are trying to compress the solid top of each SORENTO seal and that is a fail with just about anything other than low durometer silicone.

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JohnB.
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Postby JohnB. » Feb 23, 2019, 10:19 pm

The Sorrento seals are silicone.
LMWDP 267

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JohnB.
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Postby JohnB. » Feb 23, 2019, 10:22 pm

walt_in_hawaii wrote:Well, stock lands are 1.613" diameter. Mine is now at 1.640"... I will cut all 3 lands down to 1.630" and try again, which is slightly less than half the difference.... hope it works, because my arms feel like lead right now and I don't have enough strength to do this again today.


Good luck. If that's a fail just machine the stock piston for the 4th seal & call it a day.
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LObin

Postby LObin » Feb 23, 2019, 10:35 pm

Probably telling something you already know but there is a chance you messed with the thermodynamics of the TS by removing the piston while the machine was still hot. You might have to bleed the air out...
Or maybe not...
Unless it starts behaving oddly...
Or maybe it's irrelevant...
Or maybe not...
Or maybe I should've never read all of the "unstable brew temperature" thread.
:wink:

OldNuc

Postby OldNuc » Feb 24, 2019, 9:28 am

JohnB. wrote:The Sorrento seals are silicone.


The CafeLat seals are softer, that was/is the point, softer seals will function better in this case. Yes you can go too soft as well. Without actually measuring each one of these different seals it is highly likely that the dimensions are slightly different and with this tight piston fit these dimensions are now critical. Cutting the land deeper may be the fix but it may also dictate which of these seals function best. I am not a fan of hard seals in what is actually a low pressure application.

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JohnB.
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Postby JohnB. » Feb 24, 2019, 11:56 am

The Bosco silicone seals are much softer then the hard black rubber original seals & under normal circumstances seem to work better then the even softer Cafelat version. Bosco solved the seal related issues associated with this group by 2013 with a simple piston mod, a better seal & some QC improvements from the supplier that manufacturers their version of this group. The soft Cafelat seals may be a better choice with Walt's oversize piston lands but they may also wear much faster when pushed hard against the sleeve wall. Like Reiss's machined seals fix this solution may just create other issues.
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OldNuc

Postby OldNuc » Feb 24, 2019, 1:57 pm

The silicone material in any available durometer is highly wear resistant and that is just one of the several issues with the lower manufacturing cost EPDM seals that are not designed for low pressure service. As I mentioned previously the critical factor in determining the piston land depth is the width of the top, non-lip side, of the seal. You do not want to attempt to compress the thick top. Without all 3 different seals in hand I have no idea of the solid top section actual thickness, Walt does have them so before cutting twice a measurement is recommended. Excessive clearance results in seal bypass so it is a rather narrow sweet spot and best tailored for the seal to be used long term. The Teflon piston alignment ring can also be a problem on a custom piston build.

I know BOSCO fixed this issue but they are not talking either. :wink:

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JohnB.
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Postby JohnB. » Feb 24, 2019, 2:53 pm

OldNuc wrote:I know BOSCO fixed this issue but they are not talking either. :wink:


The biggest changes they made, machining the stock piston to accept a 4th seal & using their own silicone seals, are well known as I've posted that info many times.
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walt_in_hawaii

Postby walt_in_hawaii » Feb 24, 2019, 4:20 pm

For what its worth, I'd love to have a Bosco piston here to measure up; but I don't unfortunately. I've never been convinced the 4th seal was the only modification they made, but they don't seem willing to post measurements. Not a big deal, its not difficult to get the info, just a pain in the butt. My usual rule of thumb is to make adjustments by going obviously too big (which I definitely did just now), then reduce by half the distance for first adjustment. I know the stock ring land is 1.613", and I cut mine to 1.640", so half the distance would be about 1.627". This cut-and-try method is tediuous, but for a one off, doable since I'm only making one piston. If anyone else needs the info, at least it will be available from here on if they need to make one.
The new loctite I bought off amazon promptly failed! I put it only on the top of the piston shaft, so that it would hold the top of the piston shaft in the knuckle and let me just unscrew the piston at the bottom from now on and not have to use the spring compressor each time... but it didn't hold. I'm going to clean the knuckle again and try to set it again and see if it will hold it this time...

OldNuc

Postby OldNuc » Feb 24, 2019, 4:43 pm

What number loctite did you buy? There is no loctite thread locker that is really a strong grip other than 271 or 272 depending on diameter. If you want it to put up a heat required fight use 620.