Airsporter help

[hollow-point]

Just stripped and rebuilt my mark 5 airsporter using a new piston seal, buffer and spring and now its only doing 4ft/lbs. Aaargh. Any suggestions guys?

[joffy]

the seal might be a bit tight ..... try putting a few more pellets through it

[hollow-point]

how many do you reckon before it starts picking up? put about 50 through. are we talking a couple of tins? tried to sand the seal a little but it was just spinning round with it being the o ring type. not sure weather to put the old seal back in as it was still pretty tight

[Phil Russell]

Hopefully the tap is not leaking ... is it a parallel sided one? As a quick test, get a smal bit of tissue paper, load a pellet, close the tap and push the tissue loosely into the hole on top of the tap. fire the pellet ... if the tissue disappears heavenwards, the tap is leaking and will thus reduce power.
But: I have also experienced a loss of power from an over strong mainspring ... although not down to 4ft lbs so I am not sure if this could be the only reason.
A too tight O ring is possible .. was it a very tight fit ... or a very loose fit?

Cheers, Phil

[gemini163]

as above may be too tight, did you polish out the cylinder? did you test the piston, is it a nice sliding fit

[hollow-point]

it was fairly tight to get in but the old one was fairly tight to get out. the spring is supposed to be a standard one from chambers but did seem to be about 3 quarters of an inch longer than original

[cinstone]

Regarding the spring, what condition was the original? If it was in poor condition the new one would be longer. If the old one wasn't too bad, then it may be that the spring is the incorrect one.

Have a look at my Stutzen on going review on the B.S.A.O.G. It might help you out. I'm half way through the latest update, so bare with me, but i've just replaced the spring, piston seal, buffer washer & piston head retaining pin, so this may be of use.

So far i've seen an increase in power of about 1/4lb.ft after putting about 220 pellets through the rifle.

On average, with Bisley L.R.G's weighing 14.4 grain, it's giving me about 9.26lb.ft.

Chris.

[gemini163]

it was fairly tight to get in

sounds like the problem, needs to be a nice sliding fit, tight will slow the piston right down

[T 20]

how many do you reckon before it starts picking up? put about 50 through. are we talking a couple of tins? tried to sand the seal a little but it was just spinning round with it being the o ring type. not sure weather to put the old seal back in as it was still pretty tight

Don't sand the O ring, sand and polish the O ring groove to reduce the od.

With Airsporters and Mercuries I normally throw the buffer washer away and move the piston head back on the shaft.

For the O ring I use a 70 shore O ring (AS part number 212) out of an assortment box (£7.50 for 407 rings).

Fit the O ring to the piston after smearing all over with one drop of MS50, SM50 or straight silicon oil.

Smear the inside of the chamber with Silicon oil as well because once you've sized the piston head you need to clean everything again before you assemble the gun.

Fit the piston to the chamber and block the transfer port, now when you push the piston down and let go it should spring back up to where it started due to the compressed air in front of it.

If it doesn't spring back you need to reduce the ID of the O ring groove and polish it, this is why I prefer to use the Aluminium piston head and not the Nylon one.

When you have a piston that springs back, you can clean out the cylinder and fit your piston back in with the O ring lightly oiled with Silicon oil.

The O ring actually revolves in its groove when the piston moves along the cylinder so a polished groove is essential, on some guns you can actually see the O ring revolve as the piston passes the slot in the cylinder.



I have sent you some info via Email hope this helps.



All the best Mick