Londinium piston removal

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walt_in_hawaii

Postby walt_in_hawaii » Feb 02, 2019, 8:43 pm

I had a great input into an older thread I had put up when replacing my Londinium I seals. Well, I figured it was time to machine another piston for the old girl; took out the lever assembly this morning so I could measure up the piston in order to plan the modifications. I just finished making a pin wrench for the piston; inserted it into the bottom of the piston and twisted; the whole piston, shaft, and spring rotates :(
I didn't plan on making a spring compressor too... do you guys just hold the spring still and then unscrew the piston? There was some indication the piston on the Londinium could be taken off without a compressor.... but even if I hold the spring, I can see the shaft rotating when I twist, so clearly the shaft is unscrewing at the top, not at the piston end.

puffinjk

Postby puffinjk » Feb 03, 2019, 2:00 pm

Good observation on your part walt,If that shaft is unscrewing from the upper threads you are going to need to compress the spring,How do I know. :oops: Jim

walt_in_hawaii

Postby walt_in_hawaii » Feb 03, 2019, 3:53 pm

:) thanks Jim.
I cannot beiieve how cheap spring compressors are on amazon these days. When I first worked on a macpherson strut suspension in high school I had to make my own spring compressor because the price was prohibitive for a high school kid back then :(
But the ones I see on amazon have fingers that look too big to fit in the Londinium's coils, so I think I will finagle something in the garage this morning... will post pics if it works. If it doesn't, the world will never know and this topic will fade into internet obscurity... :mrgreen:

chappcc

Postby chappcc » Feb 03, 2019, 4:54 pm

My CMA group had two springs and I removed the inner spring. I don't know if yours has the inner spring - I recall Londinium has only one spring.

You need to compress the outer spring since its pressure on the piston exerts considerable force that makes turning the piston with a pin wrench nearly impossible. I made a holder for the group head assembly from a piece of 1x4 wood that I could hold in a vise.

Once you've secured the lever/piston assembly in the holder and secured it in the vise, you will be able to easily compress the spring.

To keep the spring in compression I used 14" stainless steel zip ties.

Before compressing the springs, thread four stainless steel zip ties at ~90 degrees from each other between the two springs trying to get three or four of the outer spring coils before pulling the zip tie out. A small flat head screw driver can be used to help guide the zip ties and get them out from between the coils. Draw the zip ties to tighten them slightly before you start compressing the spring. Gradually compress the springs using the lever and tighten the zip ties. You will need pliers to pull the zip ties as the spring is compressed. A second person really helps although I did it without assistance.

After you've got the spings compressed and the zip ties tight, use your pin wrench to loosen the piton/rod. It still takes a lot of force to get it loose. Remember the inner spring is still under compression, so when the piston/rod threads disengage the inner spring will release its energy. Just be clear and catch the piston/rod.

DO NOT CUT THE ZIP TIES until you have re-assembled the piston/rod assembly and you've tightened it with your pin wrench. Compress the spring with the lever and cut the zip ties - I used sheet metal shears. You can then pull out the zip ties and release the spring. You are now ready to reassemble the group.

Here are some photos.

Holder in Vise:
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Close up of the cutout for the lever/piston assembly (a 2" hole saw was used to get the opening:
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piccolo espresso

Postby piccolo espresso » Feb 03, 2019, 6:40 pm

The perfect Jig is the group itself.Remove the drip tray. Make sure you place some wood underneath the group head to absorb the spring tension when it drops.Simply unscrew the piston until the rod releases itself from the lever. The piston can only go downwards onto the wood and is safe. You will then need a pipe wrench to unlock the rod from the brass piston. Apply some heat if needed. To reassemble ,just wind by hand to connect all the pieces, drop into the group, tighten the group head screws and then using the pin wrench wind the spring upwards into the group. Really is easy and no need for dangerous jigs and ties to compress the spring.

walt_in_hawaii

Postby walt_in_hawaii » Feb 04, 2019, 1:50 am

I don't watch football, so I'm updating. sigh. It's been a trying day.
I didn't have a proper pin wrench to torque the piston off, so I had to make one. I had a pickle fork (for busting apart suspension ball and sockets in automobiles) that I wasn't using, so decided to use that... I just pressed in a couple pins without glue or anything, so I can take it apart and use it later:
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Next, I had to make a holding fixture for the group. I used a scrap piece of wood:
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I then had to make something to slip into the springs; it had to be rather slim, but strong enough to press the spring down. I had an old handle for a clutch holding tool I had made for an old motorcycle that I didn't own anymore, so I cut this up:
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It was a single piece, which I cut in two. Then drilled a couple holes for a couple small hinge plates so it could be folded around the shaft in between a couple of the spring coils. I reasoned I'd just hold the other end closed with a zip tie, then press down on both ends of the metal sticking out from the coils. I rigged everything together, but could not use a press directly on one end because it might slip off and go BOING. I needed something that would not twist off... and pressed one side of the spring down with a small tool I had made earlier for reachign in and crushing rivents inside AK47 type weapons... the other side I pressed down with a large C clamp and prayed it would not slip off. The pressure was rather low, so didn't really alarm me too much.
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There are probably much better ways of doing this, but what would life be if everyone was reasonable and everything was easy? Rube Goldberg is laughing uproariously somewhere.
Anyway, I got a little uncomfortable with how slipshod it was so quit and modified a couple large C clamps by drilling a hole into 1 jaw:
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I got rid of the Rube Goldberg setup and moved it into a vice and used both C lamps on opposide sides of the spring to pull the spring down evenly. The holes in the C clamp jaw exactly matches the diameter of the bolt in the levers sticking out from the coil, so the C clamps can't slip off and loose their grip.
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Tried to lock the shaft in padded vice jaws and twist... no go. Boy its on tight! No matter what I used, it slipped... must be a TON of threadlocker on it. I dragged out my gun barrel vice. You'll notice I didn't bother to cut exactly fitting bushings to grab the shaft; I just used bushings that were 'close enough' and figured I'd give it a shot. Kinda upset at this point and getting hungry for dinner.
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Applied heat, and it GRUDGINGLY started coming off. Man was it tight. It's cooling off in the garage now...

chappcc

Postby chappcc » Feb 04, 2019, 11:23 pm

piccolo espresso wrote:Simply unscrew the piston until the rod releases itself from the lever. .


While the sping is under tension it creates so much force on the threads, at either end, that breaking the threads loose is next to impossible. At least is my case, that is what I experienced. I did try using the group head as the jig but I could not get the piston shaft to loosen. Also, I was afraid I might do damage to the group head liner, when the spring released its energy after being loosend.

walt_in_hawaii

Postby walt_in_hawaii » Feb 05, 2019, 1:36 am

Mine had a 'soft' threadlocker on the top. On the bottom with the piston, it is a MUCH tougher compound. The top one let loose by some pressure on the pin wrench. The bottom one had no chance of coming out without heat. I wasn't counting on that little sleeve on the top of the piston... trying to design a wobbly joint in my head around that. Lemme think...

puffinjk

Postby puffinjk » Feb 06, 2019, 1:49 pm

Good job walt, These are all a little different,my group has openings in the spring housing so I have access to relive spring pressure while using a pin wrench. Now that you have been in there it gets much easier next time. Jim :D

mgwolf

Postby mgwolf » Feb 06, 2019, 3:19 pm

Walt,
Why did you feel the need to make a new piston? Just curious. I would think they're good for many years.