bsa mercury piston head

[philzack01]

I have the same on mine that i'm just reassembling and assumed that it was to keep the piston square in the cylinder.

Hi l think that this one reason why it is in there, but also to stop the front of piston head from distorting this the same on the airsporters regards phil

[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]

I have the same on mine that i'm just reassembling and assumed that it was to keep the piston square in the cylinder.

Sorry for replying to this thread a little late. The scraper ring was an attempt by BSA to overcome the tendency of the nylon piston head absorbing oil and swelling thus jamming in the cylinder. It was only partially successful and was so abandoned in favour of the later alloy head. I have just picked up an old mk1 Mercury and the piston was very difficult to remove. I have experienced this on Airsporters as well as Mercuries.
All the very best.

[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...