HW40 Piston Seal Replacement

[TonyL]

So, after many years of Weihrauch ownership, this will be my first HW that has needed anything doing (other than a couple of cheapies bought as projects or optional fettling).

I bought this new in 2010, so 15 years old. And, just now, on the odd occasion when priming, you can tell it's not building enough pressure. If you back the piston back up and then re-compress, the pressure builds.

Still blindingly accurate, though.

So, I have a new piston seal. It looks amazingly simple to do.....back the retaining grub screw off and push the pin out securing the pump rod and simply pull the piston out? Then swab the cylinder to ensure it's clean, remove piston seal and thoroughly clean the piston. Maybe dress the air intake on the inside a little to ensure no sharp edges?

But what lube? I had been thinking of just wiping a drop of Pellgun Oil on the seal. But would silicone grease be better? And anything to do to the piston body, like buffing some moly paste in or leave alone?

Cheers peeps.

[evert]

You should stay away from silicone for the obvious reason, it makes metal surfaces gall.

I'm using Mac1 secret sause on both single and multi stroke pumpers, but have no idea what it contains. I'd use 30w lawnmover engine oil if I didn't have the bottle from Mac1.

[TonyL]

Ah, thank you for that, evert.

I was going to ask if 30w lawnmower oil might be suitable, as I have some and guessed that it might fit the bill. That's what I'll use then.

Thanks again!

[Shed tuner]

pretty well anything in this low pressure, low dynamic force situation. I often use a smear of moly when doing pumpers, just because it's handy... and they all last for decades...

As per Evert, I'm cautious with most pumps that whilst the o-ring is the primary contact point, there is some metal-to metal contact on the skirt of the piston too, so I also keep away from silicone. Obviously it's fine in a 1377/22 with the plastic piston