bsa mercury piston head

[Ideot Savant]

Hi,
On the front of my mk1 mercury piston head, just in front of the o-ring, is a metal ring. Can I do without it, as it makes it very hard to put the piston back in the cylinder?
Ta,
Matt

[Ideot Savant]

Bump

[Ideot Savant]

again

[Raygun]

Not sure what you've got.

There is the Piston Head, the "O" ring that goes on it and a buffer washer that does between the head and the piston.

ATB
Ray.

[Ideot Savant]

Well, its a ring of spring steel thats just in front of the o-ring and its only function seems to scratch the inside of the cylinder. I have removed it and will try the rifle later tonight.
I could actually fit a second o-ring in the groove left behind instead, but two o-rings seems a bit silly

[Raygun]

Well, its a ring of spring steel thats just in front of the o-ring and its only function seems to scratch the inside of the cylinder. I have removed it and will try the rifle later tonight.
I could actually fit a second o-ring in the groove left behind instead, but two o-rings seems a bit silly

I'm lost on that one. I can't think why something like that should be fitted. It also sounds like the groove is a bit wide. Perhaps that's why someone tried to close it up with the metal ring ?
ATB
Ray.

[HOMER]

The Nylon head with the neoprene O ring ans steel "scraper ring" dates from the early 70's (bought mine new in 70 as a current model and is as above). BSA also fitted an Alloy single O ring head as well as a steel "Export" head ,again with a single O ring (at the front of the head), the Export version added 1 oz to the piston weight.
As you say the steel "scraper ring" really only buggered the cylinder up and is probably not worth re fitting. John Knibbs should have this version listed as a spare, I remember Hiller offering all 3 types as spares (that was some years ago though).

[badgeroy]

just in the process of reassembling my Mercury can someone advise on what lube or grease to use on the "o" ring please.

[philzack01]

The Nylon head with the neoprene O ring ans steel "scraper ring" dates from the early 70's (bought mine new in 70 as a current model and is as above). BSA also fitted an Alloy single O ring head as well as a steel "Export" head ,again with a single O ring (at the front of the head), the Export version added 1 oz to the piston weight.
As you say the steel "scraper ring" really only buggered the cylinder up and is probably not worth re fitting. John Knibbs should have this version listed as a spare, I remember Hiller offering all 3 types as spares (that was some years ago though).

l took what i said from a old book right or wrongly ? taken it out seems better as you said just cos it makes a mess of the insides regards phil

[Favsprings]

Hi All, this is my first posting. A little late?
The scraper ring was introduced as a means of reducing the build up of lubricants in the cylinder which over time was absorbed by the nylon piston head. it was discovered that the head swelled in the cylinder and reduced power. Over time this swelling caused the piston head to eventually jam in the cylinder altogether making it very difficult to remove the piston. Another thing that could occur is the buffer washer would disintergrate and the spigot on the piston would smash a hole in the head causing it to split, again making removal very difficult. BSA replaced the head with an alloy type which solved the low power and jamming problem.
This is a common problem with the early Mercuries and some Airsporters especially if they have been lying around unused for some time.

I have just acquired an old mk1 Mercury and the piston had jammed so tightly that the previous owner, upon attempting to cock the rifle, had actually bent the barrel! I've seen many bent barrels and they were always "looking up" not downwards as in this case.

All the very best.

[dalesman917]

I have just stripped down an old Mercury Mk1 that wouldn't cock and found exactly as this thread describes. Piston was jammed in cylinder and 'scraper ring' on nylon head hopefully the cause. It was also fitted with a nasty square section mainspring but that's another story. Intend fitting the steel export head and reverting back to standard spring and we'll as adding tune kit with improved spring guide.

Just wondered if anyone else has fitted the export head and was it worth it?

Great thread, searched high and low and found no reference/mention of 'extra' circlip ring until here's . Looks like at least part of the old girl remained unmolested then. Funny how it took over 40 years to cause a familiar problem...