BSA Mercury Seized Piston

[edbear2]

The last one I had to do, which was rock solid to the extent that the barrel would start to flex before the piston moved was sorted quickly if a bit messily by pouring acetone into the cylinder which turned the remnants of the buffer to a slurry.

ATB, Ed

[look no hands]

I think some sort of releasing fluid is going to be needed, then the cylinder can be placed in a padded vice and the piston tapped out via the cocking slot, once the cocking rod is out the back you can take the cylinder out the vice and put the rod in the vice and try pulling and twisting the cylinder away from the piston, they can be right buggers sometimes, the piston head in my Challenger got stuck once and I had to get a very thin and long screw driver from the bay of evil and stick it down the transfer port and beat it out.

Pete

[Phil Russell]

The last one I had to do, which was rock solid to the extent that the barrel would start to flex before the piston moved was sorted quickly if a bit messily by pouring acetone into the cylinder which turned the remnants of the buffer to a slurry.

ATB, Ed

Excellent ... I did much the same a couple of years ago ... squirted solvent through the transfer port and down the cylinder. piston moved / removed very easily. I was not convinced that the jam was caused by any expansion of the buffer washer ... more that it had disintegrated and bits of it had jammed in places around the circumference, effectively preventing free passage.
Cheers, Phil

[copperjacket]

Is a conversion to an alloy head a good idea and indeed is the buffer washer really necessary?

[Phil Russell]

I have not convinced myself that the buffer washer is a necessity. Indeed, it has been suggested that you can do away with it ... this needs the retaining pin for the piston head relocating on the spigot. Is it T R Robb who advocates this? I have never done it but increased power is claimed due to the increase in swept volume.
I have found nothing wrong with an alloy piston head. I have seen some that have suffered some abuse resulting in a somewhat damaged piston face. How this happens I am not sure but a quick spin in a lathe and a fraction of a mm taken off the face seemed to improve matters. If I remember correctly, the face had a rounded edge. Does the base of the cylinder also have a rounded profile? If not, then removing part of the 'rounding' would have reduced the lost volume as well ... not a lot though.
Cheers, Phil

[look no hands]

I have not convinced myself that the buffer washer is a necessity. Indeed, it has been suggested that you can do away with it ... this needs the retaining pin for the piston head relocating on the spigot. Is it T R Robb who advocates this? I have never done it but increased power is claimed due to the increase in swept volume.
I have found nothing wrong with an alloy piston head. I have seen some that have suffered some abuse resulting in a somewhat damaged piston face. How this happens I am not sure but a quick spin in a lathe and a fraction of a mm taken off the face seemed to improve matters. If I remember correctly, the face had a rounded edge. Does the base of the cylinder also have a rounded profile? If not, then removing part of the 'rounding' would have reduced the lost volume as well ... not a lot though.
Cheers, Phil

I've moved the head back on the piston before but only gained half a foot pound in power, which is a lot less than I was expecting but isn't too bad for 10 minutes work with a drill and saw, the last alloy piston head I took out was very thin on the face as it had a dent in it and you could see it had gone through in the spigot mounting hole.

Pete

[thisisdonald]

I tried to make an ally head for mine.. but made a balls of the pin hole.. not realising that it HAD to be oversized and that the buffer washer was required to keep things taut.
I ended up facing it off and tapping the rod right up the middle, making a delrin head to take an oring and just bonding it right on with an m4 screw. I gained some volume so had to extend the cocking slot.
anyway.. last night I made a cracking job of a fitted guide if I do say so myself I also made a BIG tophat that gives me about an inch and a quarter of preload for a skinny wee spring I found in my box.. its now doing 9fpe and you can cock it with your pinky I want to make a new tophat and then preload it with some washers to add some more weight up front.. I just need to find those washer first

[copperjacket]

Funnily enough it is a Robb head that I am trying to fit...and have made a mess of.

I like that fitted guide.

I found one set of the site screws - of course they are different for different years.

Any how 1 Mercury has now been in use all morning but I think it is really too stiff for a child to cock.

I like the idea of your 1 finger cocking tune?

[Mr. Gen]

soak it overnight then use a squared off hardened nail through the transfer port (just long enough) to get it moving, if its a blued finish a bit of heat will help - but not if you've soaked it in solvent..

[thisisdonald]

Funnily enough it is a Robb head that I am trying to fit...and have made a mess of.

I like that fitted guide.

I found one set of the site screws - of course they are different for different years.

Any how 1 Mercury has now been in use all morning but I think it is really too stiff for a child to cock.

I like the idea of your 1 finger cocking tune?

its just a thin wire weak spring.. the only one in my box that was straight and would fit!! It is pretty nice though.. ill need to get a scope on and see what its like for accuracy.. when i got this gun it had a few pellets and some bits of wood stuck in the barrel.. theres some deep pitting right in the middle. Ive not tried pushing through to check if the barrel is choked. Hopefully it is and it sorts out any problems the damage may cause

[Benelli B76]

There is a standard rubber water valve washer that makes a perfect buffer washer. You just have to drill the centre hole out to 10mm. Have posted some to guys on here before.

Baz

[copperjacket]

its just a thin wire weak spring.. the only one in my box that was straight and would fit!! It is pretty nice though.. ill need to get a scope on and see what its like for accuracy.. when i got this gun it had a few pellets and some bits of wood stuck in the barrel.. theres some deep pitting right in the middle. Ive not tried pushing through to check if the barrel is choked. Hopefully it is and it sorts out any problems the damage may cause

I will have a look in the spares box thanks. I think mine is running some sort of weihrauch reject.

[look no hands]

Mercurys seem to be fashionable again.

Really, can't say I've really noticed

Pete

[Benelli B76]

Is a conversion to an alloy head a good idea and indeed is the buffer washer really necessary?

If you leave out the buffer washer the locating pin for the piston head gets bent backwards. Anyway, why leave it out, they are easy to make ?

Baz

[copperjacket]

I was working on the basis of shortening the dowel and doing away with the buffer all together.