BSA mainseal o ring to cylinder ,how tight fit

[Phil Russell]

I have followed this with interest and my comments may not be at all relevant but ...
Do you know the history of the pistol? I ask because I was once given an Airsporter for free as it was not working ... a previous owner had tried to mend it but failed. So I was told. On receipt, the piston was stuck in the cylinder; not too difficult a fix normally and I managed to extract it quite easily. While doing so I did notice a few marks on the cylinder that sort of suggested someone had clamped it in a vice or whatever at some stage in its life. I thought no more about them. But try as I might I could not get a good performance out of the rifle. Careful monitoring of the way the piston with a new O ring went down the cylinder led me to believe that the cylinder had a bulge in it ... or rather was not a true cylinder in the region of the marks on the cylinder. Could the cylinder have been forced out of round in an attempt to hold it steady while the piston was removed at some stage? I do not know. But I thought I would try and correct it as there was nothing to lose. Now all those of a sensitive disposition should stop here because i used a hone in a drill in an attempt to correct the out of round cylinder. I am aware these tools are frowned upon by many people but, hey .. nothing to lose and in no way was I going to spend lots of money on this rifle ... In doing this I had made up an artificial piston head plus O ring from delrin, mounted on a long rod. I used this to test my results at each pass of the hone and eventually considered that I had made a decent improvement to give a smooth, regular, movement of my 'head' down the cylinder. And so it proved to be; performance improved dramatically and I was quite happy.
So ... to the point: are you satisfied that the cylinder is truly round and of the same id for all of its working range?

Just thoughts .... and maybe daft ones as well
Cheers, Phil

[original45]

It was second hand bought some month or so back.
Looks like it shot very few pellets not even a mark on plastic .
Just whipped it apart again and yet again piston was stuck tight in cylinder. Had to use cocking leaver to remove it and use fair bit of force.
Was tight all the way out not just in its compression area.

I have cleaned it out and looked inside cylinder apart from a rub at rear of piston area on upper cylinder nothing visible but I doubt IDE see any signe of buldge or simular.

The o ring is way too tight in slot but felt OK on testing for size.

Typically I can't get the god dam locking nut of back of piston head now as I used thread lock .
Tried heat and havnt Acitate .

I tried the old o ring from the o m plastic head on the stainless head and it just dropped down cylinder.
I'm now confidant the stainless head it machined in its grouve too deep for o m seal and to accommodate a 3.53 o ring not wide enough as adviced.

Had to wait 2 weeks for the head it arived with a Knut at its widest 16 mm to secure it , Spring internal dia was 14 mm how's that going to fit ?.
Had a rounded machined threaded Knut sent with a hole in but you can't get a purge on it as it sits too low in piston and slots not deep enough.

Anyone know how I can break down thread lock.

[original45]

Head off without damage to piston which was my concern. Replacement head was too small must be meteor .
Having a break for a week or so and put it all in a box until I'm patient enough to ensure I give it my 100%
Will sort another head out in the meantime .
Thanks all for your input , appreciate it.

[original45]

I have got a head today and spent most day yet again with this scorpion together and in bits.
I am at the conclusion as Phil said in a post above cylinder may have a problem.

So I have looked as best I can and I believe it could be right.
When first I was trying seals I thought the seals were too tight in the piston head o ring slot as the seal became tight on trying to draw the piston back out for inspection and replacement about half inch from bottom of the cylinder.
This was the case a couple of attempts latter.
Now today I fitted a new o ring and again as power was low I stripped it and noticed piston felt tight about 1 " from bottom as I tried to pull piston back out to 're check it.

Can anyone recommend who i should send it too to get this looked at , I just can't think of anything else it can be and don't want to bits in on the bay I hate that .
Any advice and help appreciated.
Thanks