Reply With QuoteThanks but can't see the pic? Mine has a Zephyr piston head!
Registered User
Hello again.
Here are some photos showing the strip out and condition of spring and piston head.
The gun is 1979ish (GM)MK1 Airsporter S.
I hope they may be helpful to someone.
M.
click link for photos.
http://picasaweb.google.co.uk/ultras...eat=directlink
See below T ROBB PISTON MOD
Last edited by merlin5oaks; 07-04-2010 at 09:16 PM. Reason: title change
may also be employed in conjunction with a drawn reciprocation dingle arm, to reduce sinusoidal repleneration
Thanks but can't see the pic? Mine has a Zephyr piston head!
Administrator
Originally Posted by merlin5oaks
NO MERLIN
Never use Molegrips on the cylinder like that
Besides the fact you could mark it you can also distort it.
If you need more grip, remove the tap and then insert a 1/2" chromed rod in the tap hole.
And then you need to be very careful not to apply too much pressure to remove the trigger housing.
All the best Mick
Registered User
Never put anything in the taphole other than the tap!!!! You could damage it and end up with a very leaky tap.
John
hold me back !!
Banned
It's very early for so many...tapholes
We've still only got spawn here...must be global warming..
Registered User
Hello let me know if the link does not work and I will Email you some if you like.
What shape is the Zephyr.
Cheers M
Registered User
Hello Mick,NO MERLIN
Never use Molegrips on the cylinder like that
Besides the fact you could mark it you can also distort it.
If you need more grip, remove the tap and then insert a 1/2" chromed rod in the tap hole.
And then you need to be very careful not to apply too much pressure to remove the trigger housing.
All the best Mick
Thought about using the mole grips for a while.I did not want to use the tap hole in case it got distorted or damaged.So I padded out the grips and did a couple of trial runs on some similar size painted tubebearing in mind what you said about distortion I reckoned the place I clamped was the best spot.
I think it helped applying the oil over night.
Cheers M
Registered User
Does any body have an opinion on this modification from an early T Robb tuning manual. It also seems to do away with the washer.
Click to view.
http://picasaweb.google.co.uk/ultras...eat=directlink
may also be employed in conjunction with a drawn reciprocation dingle arm, to reduce sinusoidal repleneration
They work for me now. The Theoben Zephyr is the same as the normal one, but has some channels cut in its face to reduce piston-bounce or something. The rifle certainly is powerful. The T.R.Robb buffer-removing 'tweak' should increase swept volume, it is a form of long-stoking, so a weaker spring can be used, T20 has the details, I am going to give it a go on mine. The other thing might be to machine the face of the piston flat so more space is gained that way.
Registered User
A s piston mod
So that would remove most of the radius,also what is the buffer washer for if you can remove it.I mean to say why use any way why not have a solid piston.,surely the tolerances are not that great or is it because the spring travel/bounce varies.After all we cant have the piston striking the cylinder transfer port.Aslo the question of the cocking arm 1mm tolerance to stop it hitting piston,is this not subject to wear given the force of the spring
may also be employed in conjunction with a drawn reciprocation dingle arm, to reduce sinusoidal repleneration
This is discussed on another thread somewhere, I will try and find it. The buffer washer thing is curious, because there are other designs which don't have have and seem to be OK. I wouldn't be keen to dry-fire a BSA without one in, but then I don't dry-fire rifles anyway. The chamber has to be checked to make sure the front of the cylinder is square before removing the radius, but I am sure that this is what John Bowkett used to do on his 12 ft/lb Meteor conversions. The Bowkett Airsporter and Mercury conversions were long-stroked and were, according to the stories, almost recoilless and had very short springs. I will do some searching and see if I can find some more info.
There is also the PTFE piston head sold by T.R.Robb, which is supposed to give good results, but which can deform if the rifle is not used for long periods. John Budd got much better consistency with one in his rifle.
Posting Permissions
