Yeah, that "set" is where the spring travel is moving beyond the elastic deformation stage, into plastic deformation, which is "permanent" unless stretched back in the opposite direction, beyond the elastic point.

I'm not sure why they'd have made them that way, and I'd think that moving into that range would contribute to the long term spring fatigue that causes them to get weak over time. Car springs have similar issues if pushed beyond their nominal limits.

As I said, I'm not an expert on coil springs, but I use leaf springs heavily, and what I've seen of all springs, is that you typically want to design them to be operating only within the elastic range, and with a margin of error, for long term durability and consistency of force. Although springs were often run much softer in terms of hardness, and stiffer, in terms of thickness, than we run now, and fatigue is common under those circumstances.

They are ultimately consumable, but there's a lot that can be done to make the longevity so high, under light use (of which all consumer use would fall), that they shouldn't fail in any reasonable life-span.



So, baldheadracing; do we think the old spring from your 1985 model, was originally shorter also, than the new spring, or that it lost ~15mm in height over time? (this seems unlikely to me)

Just to update, finally recovered from NYE debauchery, haven't forgotten about this, just didn't have a chance to make progress with all the liver damage I had to do first.

I'll report back once I get mine taken apart, can compare to the numbers I've got here so far. It'll be a couple of weeks before I see somebody that can give me some input on making the new springs also, but I'll keep pursuing it.

Thanks all, for the help.

I have two about-1990 MCALs and I confirm that I installed on both machines new springs without any problem. Moreover I installed on both a second spring also, to have more power.

I found in my phone this image of the mod of my newer MCAL

I am also replacing my spring on a slightly newer 1991 MCAL. The length of my old spring is also 68mm, but my extractions before would result in about 10s of crema followed by what I would almost called choking, where the lever would become extremely slow until completion. I will try the new spring without gaskets in the piston and the bottom of the cap and will use silicone grease (I have admittadly not used some since I bought the machine and may be part of the issue).

Here is the jig I created using 0.707" plywood, 5/8" bolts with 1" diameter nuts.