Londinium piston removal - Page 5

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OldNuc

Postby OldNuc » Feb 17, 2019, 10:15 pm

Now to put it all back together and see if it works. Should seal better anyway.

walt_in_hawaii

Postby walt_in_hawaii » Feb 18, 2019, 1:13 am

That might be awhile :(
I can't find my loctite. Blah. Had a new tube of it somewhere... where'd I leave it??
Anyway, drilled the holes... the stock piston has 2 holes in the working face for the wrench; I didn't like that, so I put a hole in the side and will use the pin wrench shown to torque the piston on and off. Hopefully. Its a pretty small wrench compared to the one I used to take it off :(...hope it has enough leverage.
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pizzaman383

Postby pizzaman383 » Feb 23, 2019, 2:26 pm

Very cool!
Curtis
LMWDP #551

walt_in_hawaii

Postby walt_in_hawaii » replying to pizzaman383 » Feb 23, 2019, 2:57 pm

Hey Curtis. Not sure how cool, but we'll know a little later today.
my new tube of threadlocker arrived last night and I put some on the top of the shaft and installed it... supposed to cure 24 hours, but I can't wait :)
so, I assembled it:
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and installed the seals (SSOOOOOOO easy with the new seal tool!) ..note I am re-using the sorrento seals, they have a handful of months on them and for my purposes, they are slightly stiffer than the silicon cafelate but softer than stock seals, so represent a good halfway modulus to gather data about sealing pressures (at least that's my seat of the pants opinion)
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After seal installation and pushing it down into the group head... I was holding my breath. I had to guess at the land depth and left it rather 'high' at 1.640" diameter, if its too tight it would be a simple matter to take the piston out to trim it down slightly deeper... it was very stiff going down, but went in smoothly after the first seal made a slight noise something like you'd hear in your proctologist's office... :)
Buttoned it up, machine is heating up now. Will get back to you in a bit. I took one lousy pic from underneath, wow that piston is tight fitting now! i have to scrape away the excess lubricant, but it looks much, much closer to the walls than the stock piston. Also, no holes in the face!
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walt_in_hawaii

Postby walt_in_hawaii » Feb 23, 2019, 3:00 pm

Oh yeah, in case anyone was wondering.... that lever is now SMOOOOOOOOOOOOOOVE!!!!
...but, surprisingly, no additional effort to lower it. Effort feels the same, a good sign.

pizzaman383

Postby pizzaman383 » Feb 23, 2019, 3:22 pm

That is very interesting. I have found the Bosco seals to of be tighter in my group sometimes even so tight I struggle to remove the piston if the lube has washed off. My piston must be larger or cylinder tighter.
Curtis
LMWDP #551

walt_in_hawaii

Postby walt_in_hawaii » Feb 23, 2019, 3:56 pm

HOLY SMOKE! its tight...
The stock setup is pretty free moving, lever can be moved against only the spring pressure and you feel a soft stop as it comes up against the pressure of the puck. It is now so tight (when hot), it is difficult to spot the soft stop, there is a lot of resistance to movement. Also, pulling the lever down at anything less than a crawl will lift the back end up off its legs!
...piston has to come out. I think I'll trim .010" off the lands. There was no scraping or rubbing sounds, so the piston outer diameter appears to be fine, its just the seal lands are too tight and pushing the seals too hard agianst the walls of the cylinder.

pizzaman383

Postby pizzaman383 » Feb 23, 2019, 4:00 pm

I am now using the Cafelat silicon seals because they are a little smaller and softer than the Bosco seals so they have just the right amount of clearance.
Curtis
LMWDP #551

User avatar
JohnB.

Postby JohnB. » Feb 23, 2019, 4:03 pm

If you are going to pull it out again why not machine the piston for the 4th seal? You must have noticed that there are no Bosco owners complaining about seal related issues.
LMWDP 267

walt_in_hawaii

Postby walt_in_hawaii » Feb 23, 2019, 6:52 pm

Hey JB! Afraid I can't :( I moved the location of the topmost seal, since there was a ton of space that wasn't being used... I moved the top seal a little higher to use some of that 'empty' space. I could have made the piston either the same as stock, and added the 4th seal, or made it slightly taller and added another seal, but I figured 3 seals were working mostly ok most of the time, so just left it at that. Might have been a bad call, but there it is. But, I know that other machines are working just fine as is, so the seal problem is only a marginal one... so my reasoning was just a bit of assistance was needed but didn't require going with 4 seals.
For what its worth, I think I made the right call. I worked on it while it was still rather warm so that the group would be easier to come up... still had to hold the group using a rag as it was too hot to hold; but it was just about impossible to lift it, the suction was THAT strong. And, now that the piston is so tight fitting, I cannot rock it back and forth to break the vacuum stiction effect. I worked the lever and finally got the seam to show just a tiny space, and put a soft pry bar inside; then operated the lever and got enough space to shove a book in there; then 2 etc etc... man was it STRONG. I was lifting hard enough for the entire machine to come up at times. With a hot machine, not a lot of fun.
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.