Bren body housed at Warminster ....

[jmoore]

I made steel oblongs to fit the Mk2 early Canadian front ports and wrapped wire around the whole mess to get my semi to run. Way ugly but its working.

Information

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[Peter Laidler]

Good idea JM but what you really need is a new gas cylinder without the front set of ports. I'd try a new piston as well. But at least you proved that it was a worn gas cylinder. We had a puller that worked on a screw thread system, that would draw them ont, for changing the Mk2 cylinders

[jmoore]

That sort of tool should be easy enough to make. Its quite helpful to see that picture of the various gas cylinders side by side!

Now to round up a servicable replacement.

[Peter Laidler]

Please keep a photo record and let us all know how it goes. We have a special all singing and dancing alignment jig fixture thinggy. You know the sort of thing. A bit like the No4 barrel breeching up alignment gauge. Used during your apprenticeship but out in the real world, a much simpler method was used called common sense, eye sight and the bleedin' obvious!

Anyway, keep the needy among us informed of progress

[Brit plumber]

Peter, Could the forward set of holes been there to actually help get rid of carbon? I always beleived the idea was that as the gas cylinder caked up with carbon, you rotated the gun on the bipod which broke up the carbon and it was exhausted out of the ports. Obviously this didn't work in practice, but was that the idea behind it?

[Peter Laidler]

You're dead right of course Britplum. That was the theory and, sadly, the practice too. It was all to do with using cordite ammo and the fouling issues it presented. But the first set of holes were EXACTLY in line where the blast of gas hit the face of the piston. The huge blast drove the piston back AND vented into the holes too. But hang on a minute......, there were another 6 identical holes not half an inch to the rear of them, waiting to do exactly the same job just as effectively! So the front holes were redundant before we get off the plane! So why have them in the first place? We had them to prevent a ring of hard carbon ring building up there. And if not cleaned, the build-up could and would prevent the piston from going fully forward. But at least you could clean it. The later closed off gas cylinders have a recessed cannelure inside and that's the reason why the later guns had a TOOL, removing fouling in the kit. You know the thinggy, a small plier shaped set of cutters that will only go into the cylinder so far. Problem solved!

The REAL rub was that the gas cylinder was a factory fitment only (until about 1945) and not supplied as a spare part. So as soon as the trusty....or now NOT so trusty Bren, reached gas port number BIG, it ran out of gas. And there it stayed, effectively..... and we come across those magic initials again....., ZF. The trouble was that there weren't the facilities to send them back to the factory from battlefield France.

As I mentioned in the Mk1 barrel saga, you could open up the gas vent in the barrel to .148" or so and get MORE gas but that was a palliative and not a cure. Because when you had a perfect gas seal/new cylinder and no leaks via the front holes, the new volume of gas would send the piston post crashing into the breech block during the unlocking phase...................

It goes on and on, getting worse. Think longer piston post plunger, deeper piston posts, tougher piston post spring, double return springs, broken buffer plates............... phew!

The Mk2 gun solved it and the Mk3 perfected it

[Brit plumber]

Thanks Peter.