HW100 Cylinder Seal Replacement

To remove the end caps from the cylinder I used a couple of special tools from HW100Tuning. The first is a tommy bar which inserts into the filler probe hole and the second is a “Lawrie Spanner” a socket which fits the flats on the block end cap and is turned with a 30mm spanner. Without these tools removing the end caps without damage is virtually impossible.

Even so my end caps were very tight and clamping the cylinder is difficult. Initially, I covered the cylinder with some old inner tube and then clamped it between wood blocks in a vice. But I didn't want to tighten the vice too much and I just couldn't stop the cylinder from rotating every time I tried to loosen the end caps.

Shown below is the method I eventually hit upon: Two strips of leather from an old belt clamped around the cylinder with Jubilee clips and then the whole lot clamped between wood blocks in the vice. The wood blocks themselves have a groove routered into them to better grip the cylinder.

And success! I was able to clamp the cylinder firmly enough to get both end blocks off without damage. You need to engage the tool and then tap the end of the tool or spanner with a rubber mallet to crack the caps loose, then they can be unscrewed by hand. Once they're off you'll need to remove the valves from the end caps. Again, these are tight and you'll need a plain slotted screwdriver or driver bit with a tip 10mm across. Don't be tempted to improvise on this because you will chew up the slots.

Once the valves are out replacing the seals is easy – pull off the old and replace with the new. Smear the new seals with a small amount of the grease provided before fitting and don't be tempted to use anything else.

When replacing the end caps, they don't need to be mega tight. I did both hand tight and then nipped them up just beyond that using the tools. Top the cylinder up to 150BAR before refitting it to the rifle and the job's a good 'un.