Dan, thanks for the tip on the molasses and the offer of steel end plates. I'd read somewhere that you suggested a 4 day soak for the molasses, which is why I ended it relatively quickly. The steel end plate would be great, but I've already handed my spring clamp to my contractor. I'll let him have a go at it and if it's not up to snuff I'll take you up on your offer. Much appreciated.

Still stuck trying to unscrew this piston so I can clean it up and change out the spring. McDave at Allann Brothers has a new spring on order for me and a new can that fits on top of the group so I can ditch the corroded one. His instructions for unscrewing this piston are as follows:

"1...The piston is threaded top and bottom.
We don't separate it at the top because of that roll pin.
The rod has either two flat sides or a hole through it at the middle of the spring section.
Hold the rod still and unscrew the gasket head until it comes off.
There is a large ss washer in there placed only at the top of the spring."

Here's what I'm trying to do:

"Hold the rod still and unscrew the gasket head until it comes off."

I've sent an e-mail to follow up. But meanwhile maybe someone else is reading this who's taken apart one of these.

I assume the "gasket head" in his instructions is the bottom part here that holds the gaskets:



Here's how the top of my piston rod looks:



I've not yet obtained a pin spanner like erics suggested. I did measure the hole in the piston. It's 6mm. Pin spanner wrenches cost a minimum of about $20 before shipping. I did try a padded bottle opening tool while securing the piston assembly in a soft vise. I had reinserted the pin so the rod wasn't turning. It would not turn out counterclockwise.

Christopher Cara, whose father imported my machine, told me they used to clean these piston assemblies by immersing them in vinegar and boiling them. Maybe that will help me get it loose. But if anyone who's done this can tell me how to get it apart, I'd be most grateful!

I'm guessing the job will be made easier if the spring is compressed some since it exerts a good amount of force on the piston. I think this might be a job for the zip-tie trick so that you can compress the spring separately from the piston.

Actually when I turn the piston and rod, which move together, the spring easily slides under the cap. I don't think it's exerting much pressure.

Can the rod/spring assembly be removed away from the bulk of the frame (up top there), now that the pin has been removed and freed from the clevis thing.

The pin spanner might help. However, if that piston is brass, I would be very, very careful.

#1 on the list is soaking the threaded area (where the rod threads into the piston) in WD-40. I would say for at least a couple of days wouldn't be a bad idea.

It might not be a bad idea to also put the assembly in the freezer for a day and then use a torch to heat up the head quickly (don't go crazy, but maybe to 300-400 degrees).

Also, it's important to understand the difference between exerting force on something like this verses using impact. Often times a lot of small impacts (or one impact) will work better to free something than applying a sustained force (which tends to be more prone to bending things). It depends on the yield strength of the material you are working with, etc.

Anyway, on the piston part, is there only one 6mm hole or are there more? You might want to consider building a special tool if there are multiple holes. Also, in these sorts of situations, just remember that your three best friends are usually WD-40, heat/cold and patience.

If you want to make a short video and upload it to youtube, I will be happy to take a closer look at what you have going there and see if any other ideas jump out.

Ray

Good ideas, Ray.

There is only one 6mm hole. As far as adding heat, I may go with Christopher Cara's suggestion and boil the whole thing in vinegar for awhile. That should dissolve and loosen things up and may give more penetration where it needs to happen than WD-40 applied from the outside. I would remove all the lever pins and c-clips first, of course. This morning I noticed there was coffee residue in the 6mm hole so it's likely sludged into the rod where it threads into the piston. I don't know how much a video would help. If boiling in vinegar doesn't do it I'll give McDave a call because he's actually worked with this thing and there may be a simple trick to get it to yield.

WD-40 penetrates surprisingly well. You might try that first (let it sit over night at least).

I think if it were me, here is how I would approach this.

1. Spray with WD-40 where the rod threads into the piston

2. Hold the rod in a vise, using a long wooden V-block perhaps (maybe lined with some rubber).

3. Attempt to loosen with a pin spanner by hand (without going crazy).

If that doesn't work, then I think I would take a 1/2 impact socket and use a lathe to turn the inside to the exact same diameter as your piston there (+ .001). Then drill a hole through the wall of the socket, which perfectly matches the location of the 6mm pin and thread that (or weld a boss where the hole goes). Then make yourself a threaded indexing pin with a hardened tip, that will thread into the 6mm hole.

You get the idea.

Then index that onto the piston and use a good quality impact wrench to remove the piston. Not much can withstand the force of an impact gun - I don't care how seized up it is. And also, as mentioned previously, impact is usually better than leverage force.

Ray

Thanks, Ray. I'll share your thoughts with DJR if I need to punt and have him help me with this because he has the tools. But I'll bet it's easier if I can just get a hold of McDave. The piston assembly appears to be in good shape. The whole thing was operating very smoothly when I removed it. I doubt I've got anything going on like the frozen bolts that had me stuck for so long.

Sorry if this has been asked but what does the bottom of the piston face look like?

Thanks for asking. It's an absolutely flat surface of solid brass. This photo gives you a sense of it and shows the one hole in the side that measures 6mm. But your question and Ray's and Dan's offline got me thinking. I took a wire brush to where the bottom of the piston joins the larger part that holds the piston rings.



I've now added WD-40 to what looks like it may be a seam.



The first photo I just took to answer your question showed me something new, a tiny hole. There are three of those evenly spaced along the wider ring. This photo just taken clearly shows two of them.



Also Dan asked me to locate the flat part of the rod or the place where there's a hole per McDave's instructions. There's no hole. The rod is flattened on both sides toward the bottom, where it meets the part that holds the gaskets. Getting anything through to grip that would be a challenge. The spot there is not a hole but a bit of dirt I just cleaned off.



Per Ray's suggestion in the morning, when I can make some noise, I'll give the bottom of the piston a whack with a rubber mallet to see if I can loosen it up. If not I'll apply more WD-40.