BSA Airsporter / Merc trigger block issues

[edbear2]

Reading through the thread on the Merc elsewhere, I thought I would add this as I am in the process of fixing an Airsporter which was a bit rattly. The gun felt "loose" on cocking so after the grip and forend screws were tightened, a single shot was fired which showed a healthy 580 fps with wasps (bit shy of 11).

Anyhow, on stripping, the back block steel threaded cup which engages with the cylinder was quite loose, so I was relieved that the back block unscrewed by hand. For anyone who has never had one apart, the general arrangement is shown here;

https://www.flickr.com/photos/312284...57663274889756

The threaded cup is retained by the screw in part with the thin flange, the cup is drilled in three places around it, and in these places when the gun was new, the flange of the screw in part were upset by a punch or press tool to provide a locking function. Although my cup had about 10 degrees of "rattle" I still needed to drill through the holes to remove material that was preventing turning, this is a 2 min job, just use a close fitting drill and give each hole a couple of "pecks" till clear. I used an airline chuck locking tool with angles ground in it as a driver, these are often found at car boots cheap and I have a small biscuit tin full of the things as they are a great source of cheap flat stock steel, besides being a ready source to make into tools for jobs like this (Diana 50 stock bolt was another time one saved me!), Older bicycle spanners are good quality steel too, and are normally pence.

On this gun, I may now try and get the stud out and get it anodized as a TX block I had done recently came back in super order, I will then assemble using an oil tolerant high strength Loctite, maybe 602 but undecided as yet.

The radial anti slip grooving on these bits are a real bit of quality, and prevented my cup spinning and causing a disaster, even though the thing was loose, but obviously if you have any discernible movement....No excuses not to sort it out!

Couple of other things I could add, the ONLY way I ever get off BSA / HW blocks if tight is with a superplastic Thor. Nothing else comes close, never use a bar in a BSA as the leverage is nowhere near what a sharp rap with mallet will do...Think impact airgun on wheel nuts, A sharp rap has the same shifting effect.

I also will only use mousemilk or plusgas, a few moments with a hot air gun to cylinder joint, apply penetrating fluid, leave till cool to touch, one or two whacks with a mallet, has never failed....ever!

On HW's I use a block of steel which fits snugly in the trigger pocket and protrudes maybe 60mm, but must be a slip / light push fit to prevent marking.

ATB, ED

[frogboy]

Great thread Ed,

took me couple of reads to understand it, fascinating how the engineering of these things works, and at some point someone was sketching this out as a new design.

still counting my winnings from Thursday.

Lee

[Airsporter1st]

Great thread Ed,

took me couple of reads to understand it, fascinating how the engineering of these things works, and at some point someone was sketching this out as a new design.

still counting my winnings from Thursday.

Lee

Yes - you can see why the Airsporter/Mercury were so expensive in their day. Weirauch and others of course simplified the whole thing greatly by screwing together the trigger block and cylinder and then finish machining to give perfect alignment time after time (unless someone overtightens and stretches the threads, of course).

I use the same flat steel bar for Weirauchs, but I use one slightly thinner than the trigger slot and wrap it with insulating tape. This causes it to be slightly less effective in transferring the force of the blow, but lessens the risk of damage to the block.

[ggggr]

Reading through the thread on the Merc elsewhere, I thought I would add this as I am in the process of fixing an Airsporter which was a bit rattly. The gun felt "loose" on cocking so after the grip and forend screws were tightened, a single shot was fired which showed a healthy 580 fps with wasps (bit shy of 11).

Anyhow, on stripping, the back block steel threaded cup which engages with the cylinder was quite loose, so I was relieved that the back block unscrewed by hand. For anyone who has never had one apart, the general arrangement is shown here;

https://www.flickr.com/photos/312284...57663274889756

The threaded cup is retained by the screw in part with the thin flange, the cup is drilled in three places around it, and in these places when the gun was new, the flange of the screw in part were upset by a punch or press tool to provide a locking function. Although my cup had about 10 degrees of "rattle" I still needed to drill through the holes to remove material that was preventing turning, this is a 2 min job, just use a close fitting drill and give each hole a couple of "pecks" till clear. I used an airline chuck locking tool with angles ground in it as a driver, these are often found at car boots cheap and I have a small biscuit tin full of the things as they are a great source of cheap flat stock steel, besides being a ready source to make into tools for jobs like this (Diana 50 stock bolt was another time one saved me!), Older bicycle spanners are good quality steel too, and are normally pence.

On this gun, I may now try and get the stud out and get it anodized as a TX block I had done recently came back in super order, I will then assemble using an oil tolerant high strength Loctite, maybe 602 but undecided as yet.

The radial anti slip grooving on these bits are a real bit of quality, and prevented my cup spinning and causing a disaster, even though the thing was loose, but obviously if you have any discernible movement....No excuses not to sort it out!

Couple of other things I could add, the ONLY way I ever get off BSA / HW blocks if tight is with a superplastic Thor. Nothing else comes close, never use a bar in a BSA as the leverage is nowhere near what a sharp rap with mallet will do...Think impact airgun on wheel nuts, A sharp rap has the same shifting effect.

I also will only use mousemilk or plusgas, a few moments with a hot air gun to cylinder joint, apply penetrating fluid, leave till cool to touch, one or two whacks with a mallet, has never failed....ever!

On HW's I use a block of steel which fits snugly in the trigger pocket and protrudes maybe 60mm, but must be a slip / light push fit to prevent marking.

ATB, ED

Hi Ed--good work there. I have often found the later blocks are harder to remove than earlier ones. Maybe they swung on them in the factory rather than adjust them?
I had a Mk4 ish one given to me and the cup was loose/not engaging with the serrations on the block, which were worn. The cup remained in the cylinder and I had to use a drill to make 2 holes and then find something to unwind it.
On Chambers diagram a lockwasher is shown between the cup and the back block (WO 11) https://www.gunspares.co.uk/products/24686/Mk4/ but there was not one on mine and does not appear to be one in your set up. As the alloy serrations in the back block were worn on mine, I obtained a 2nd hand block and fitted that. I didn't fancy my chances of cleaning up the serrations on the block with a hacksaw and needle file and then it holding, even if a lock washer was used. I guess Stud lock might have helped but the 2nd hand clock just seemed the cheaper/ easier/ better option.

[El Garro]

An old motorbike brake pad makes an excellent HW trigger block took, soft enough not to damage the metal on one side and metal to hit with t'hammer on the other
Usually available for free too !
(Apologies for going off thread a little)