Yeah, I think the shaft collar, with a slightly modified set screw might be the best answer here. This would give you the most secure engagement and then all the forces could be applied to the collar, not your piston.

Seems to me getting a shaft collar, then welding a socket onto it (or something) would produce a very handy tool for this job. I would think your total cost might be less than $40

What's the outside diameter of that piston where the 6mm hole is?

Ray

Or you could mill a couple flats in the outside of the collar to hold it in a vise. (Or six flats and make a nut... ok we're getting carried away. This just needs to be tapped loose and tapping doesn't work well unless the part is being held firmly...)

I think garage has a grinder (?). He could probably order a collar and then grind a couple of flat spots. Modify the set screw to engage with the 6mm hole and he would be all set.

If you have amazon prime, I bet you could do this for less than $12!

I'm still happy to fabricate up a tool for you, although I have to check and see if I have a any gas in my welding tanks. If not, then that could be a problem, since my girlfriend and daughter have my truck right now (and hiking a tank full of gas on my motorcycle probably wouldn't be too fun haha)

Ray

Once again, apologies for being a pest but why are you doing all this in the first place? The spring looks fine to me...no rust or pits, etc. Is this a personal challenge type thing, you know, a personal growth experience, or is there something verifiably wrong with the current spring?

LOL "a personal growth experience"

Gotta love Doug

Ray

orphanespresso wrote:Once again, apologies for being a pest but why are you doing all this in the first place? The spring looks fine to me...no rust or pits, etc. Is this a personal challenge type thing, you know, a personal growth experience, or is there something verifiably wrong with the current spring?

Ah yeah ... more insecurity than personal growth, Master Yoda. The spring was locked down for more than a year. Doesn't that create metal fatigue and weaken it a bit? A new spring is less than $16. I wanted to make sure my restored gem would work at factory spec.

What do you think of the La Cara method of cleaning it up by boiling it in vinegar? I would remove the pins, clips and chromed lever base first.

@ Ray and Dan, I like the collar idea. OTOH if Doug says I'm crazy to take it apart that is something to consider and then move on.

The spring is probably fine. However, you've come this far... if the new spring is only $16, I say forge ahead. I think the shaft collar idea is cheap and will work well.

As far as the whole boiling in vinegar thing, I personally would stick with WD-40 myself. Something about combining heat and a mild acid against metal doesn't sit 100% well with me. Reminds me too much of an incident with parkerizing a gun frame. The gun was (and *was* is the key word here) from the early 1900's (belonged to my grandfather and was the only thing I had from him). I decided it would be a great idea to strip the gun down (i.e. remove the bluing) and then parkerize it. The first attempt wasn't half bad, but then I decided it needed to be darker. I did a quick media blast to clean it off and tossed it back in.

The was the end of that. The metal wasn't as strong as I thought or it was some strange alloy or something. The surface was destroyed and the tolerances were changed enough to where the slide didn't even look like it went with the frame. I ended up smashing everything with a sledge hammer out of disgust and throwing it into the recycle bin.

So ever since then, I've always been super careful when people start talking about boiling metal in different solutions. Not saying vinegar is anything horrible, but just keep in mind that certain metals can have strange reactions sometimes. I think, for my money, if you can accomplish this without boiling your parts, that might be preferable.

Ray

Hi Ray:

If it was just anybody I would hesitate more. But Christopher Cara told me that. He and his dad imported my machine and Christopher learned from his dad how to service them. The metal would be all brass except for the steel spring. Vinegar is also pretty mild as far as acids go. And I wouldn't boil it for more than about 20 or 30 minutes.

I brought the spring with me to maybe get it to a bike shop. To give you a sense of the heft of this piston group, here it is next to my pre-M Pavoni. Both are vertical. The iPhone photo distorted the perspective but not the size.

Also, keep in mind, if you snap that rod in half or something, then Doug's wisdom here about leaving everything alone will prove to be very sage advice

My guess is the spring is fine. However, I definitely relate with you as far as wanting to take everything apart and have every inch of the machine clean and brand new looking.

But... I think if you are going to remove the piston, you really need to approach it from the correct standpoint. If it were me and this were my machine, I think I would take the time to fabricate up a shaft collar that fits perfectly over the piston. Then make myself an indexing pin that engages with the hole. Then weld on an old impact socket (or a new one for that matter) to the top of the collar. Then use an impact wrench to spin off the piston, while holding the shaft with a wrench (that is secured in a vise).

I think that approach would minimize any potential damage to anything. I would be surprised if the impact wrench didn't break it free almost instantaneously.

Using any other method, my concern is that leverage could bend the rod and/or twist something along the axis that might cause issues for the smooth action of the lever.

I think if you aren't going to really approach it from the standpoint of using an impact wrench, you might want to leave well enough alone and take Doug's advice here.

Ray