Airsporter MK1 trigger doesn't catch

[TeeD]

Last afternoon, my Airsporter MK1 .22 called it a day. One moment it was a happy shooting relic, the other moment it refused to catch on the trigger.

After opening it up, I saw that the pin inside the piston all of a sudden seems too short. When pulling back the underlever, this piston pin should push against that hammer-like part in the trigger assembly and hook behind it, but it doesn't. It just doesn't push far enough to free it from the trigger. There's just one or two mm extra needed.

It's not the trigger itself that needs adjusting, I made sure to look at that. Even disassembled, so without spring, I can not push that piston pin in far enough manually. I can see there's a thread that goes into the nose cone, but it's stuck solid. Besides that it seems impossible to adjust, because if loosened, it will rotate itself until tight again or completely loose.

Doesn't seem to be any excessive wear on the metal parts and if it were, one would expect a period of on/off functioning before going definitely off.

Any ideas on this one?

[flatrajectory]

It sounds as if there is some wear in the cocking linkage somewhere. The most likely place to look is the rear end of the cocking slot in the piston and also the end of the cocking linkage where it pushes back the piston. Try a blob of weld on the end of the piston cocking slot, suitably polished and finished off ,of course.
Pete.

[Airsporter1st]

Last afternoon, my Airsporter MK1 .22 called it a day. One moment it was a happy shooting relic, the other moment it refused to catch on the trigger.

After opening it up, I saw that the pin inside the piston all of a sudden seems too short. When pulling back the underlever, this piston pin should push against that hammer-like part in the trigger assembly and hook behind it, but it doesn't. It just doesn't push far enough to free it from the trigger. There's just one or two mm extra needed.

It's not the trigger itself that needs adjusting, I made sure to look at that. Even disassembled, so without spring, I cant push that piston pin in far enough. I can see there's a thread that goes into the nose cone, but it's stuck solid. Besides that it seems impossible to adjust, because if loosened, it will rotate itself until tight again or completely loose.

Doesn't seem to be any excessive wear on the metal parts and if it were, one would expect a period of on/off functioning before going definately off.

Any ideas on this one?

Is the loading tap coming up fully? I seem to recall having a similar problem caused by the loading tap indexing plate coming loose.

This can also happen if the trigger spring is broken - resulting in the sear pivoting upwards at the front end and thereby preventing the piston rod from entering the trigger housing.

[TeeD]

Cheers!

The loading tap is coming up fully and the piston can be pushed as far back until it hits the trigger housing, so no play there. The trigger spring is okay and seem to be all the other parts.

It's just that pistonpin that seems to have shortened. There's a bit of play where the seal is on the nosecone, but I can't seem to tighten or even disassemble that. Even with the cone treated with penetrating oil and hold in a vice (hate that), it just starts to damage the tip by twisting. It's that solid.

But that shouldn't be the problem, because even if I push it completely back by hand, the pin doesn't push back far enough. Strange, isn't it?

[Airsporter1st]

Cheers!

The loading tap is coming up fully and the piston can be pushed as far back until it hits the trigger housing, so no play there.

It's just that pistonpin that seems to have shortened. There's a bit of play where the seal is on the nosecone, but I can't seem to tighten or even disassemble that. Even with the cone treated with penetrating oil and hold in a vice (hate that), it just starts to damage the tip by twisting. It's that solid.

But that shouldn't be the problem, because even if I push it completely back by hand, the pin doesn't push back far enough. Strange, isn't it?

Very!

I guess you have already had a good look at the x-section on Chamber's website. This should hlp you see what is wrong.

If the piston rod were to come loose, the overall length would increase, not shorten. It sounds like something has broken or come adrift in the trigger mechanism.

At least its a definite problem and not intermittent, so the cause is just waiting for you to find it!

[TeeD]

It's pretty definite indeed, so you would think the fault would present itself in a silver dish.

But it doesn't...

As you can see on the picture, the piston is almost hitting the triggerhousing when it starts to engage the little hammer-like thing.
Uploaded with ImageShack.com

But with the limited travel remaining, it doesn't come further than this:
Uploaded with ImageShack.com

The play in the piston tip is nothing more than this:
Uploaded with ImageShack.com

And the wear on the parts is next to noting:
Uploaded with ImageShack.com

[jjjjjj]

I take it you have undone the nut inside the piston, it sounds to me that the nut inside the piston is lose and that's why its not cocking.

[pennineway.fswo]

I take it you have undone the nut inside the piston, it sounds to me that the nut inside the piston is lose and that's why its not cocking.

Agreed

I have found this on a couple of Mk1's that refused to latch up

If the nut is not fully tight the cocking linkage pushes the piston back but the central rod and head/cone of the piston (they are 1 part) does not then travel back sufficiently to trip the sear in the trigger block

John

[pennineway.fswo]

If after fully tightening the nut inside the piston the problem is still present then it can be just wear and tear on a number of parts including the backend of the cocking slot and even wear or breakage in the pins through the trigger assembly

Assuming everything else appears to be OK then the tip re. weld metal being added to the back end of the piston cocking slot should be the answer. This effectively ensures that the piston is pushed back on cocking just another 1 or 2 mm more
John

[pennineway.fswo]

Just seen the pic of piston head

This must be fully tightened!!!.

Even a gap of half a mil. will give you a problem

You can make up a tool to tighten the nut using a box spanner (it may need rounding off externally slightly to go inside the piston)

John

[TeeD]

Ah, that could be it! Never noticed the nut in there to be honest, stupid to think there would'nt be a counternut...

I'll give up a box spanner for the good cause, thanks for that tip.

Vingers crossed that'll be it and otherwise a tiny bit of welding would do, but I try to keep that as a last resort.

Will keep you informed about the progress.

[Gunman61]

Did this gun ever cock ,did you try your finger behind the trigger to bring the trigger forward to see if it would cock then.? If i dose your spring is in the wrong place.

[TeeD]

FIXED!

It was indeed the nut in the piston that had come loose. With the box spanner conversion, it all came together again without problems.

And talking about nuts and spanners, not seeing there was a nut inside was pretty stupid of me.

Thanks for thinking with me!