• the Daily hi thread just say hi :)
  • please everyone if you have a question and get given a possibe solution if it works please update your thread as it may help others.

Chopping a TX piston to create a skirtless design?

E

E30_318is

Member Extraordinaire
Joined
Jul 8, 2022
Messages
3,754
Reaction score
9,801
Location
West Yorkshire
Just thinking out loud here and drawing inspiration from the various skirtless pistons available aftermarket for the likes of TXs and Prosports.

Has anyone ever parted off most of the body, leaving behind just the head & first bearing recess that runs in the comp tube, omitting the rear section of the piston? There would be considerable weight savings to be had using only factory parts...

Perhaps the bearing at the piston head would need to be remade to a closer tolerance to keep the piston running central since there'll be no rear bearing & not much support for the spring, or place a delrin disc between the tophat & spring, or have the top hat base oversized to act as a second bearing?
 
Never done it, but was musing of the possibility today myself.

I'd assume that's where the smaller 22mm and 21mm ones started, before they reduced diameter, so there's probably a good reason the skirtless pistons are reduced.

It may well be that a longer piston head is needed to keep the piston concentric to the compression chamber bore as you suggest, or it could be that there's a sweet spot with the piston weight to balance out the difference in inertia caused by friction on the pellet in the bore with different pellet weights, or a combination of the two, or something I've not considered!

It would be interesting to find out just how much piston weight could be removed before efficency drops off, and certainly the skirtless pistons that have been produced suggest there's a lot more efficencies to be had in springers!
 
I'm sure someone far more knowledgeable than me has posted this before but the reason the 21mm/22mm kits are so good is the fact they run a smaller diameter and stroke.

They are the most efficient and optimum size. The way the OEM and 22mm pistons build pressure is totally different.

Chopping up a standard piston isn't the same thing and it's probably not enough to get the full benefits of a tune like this. It can probably be done if you play with the stroke too, but honestly just stick your hand in your pocket and get Tony Leech or someone similar to sell you a kit. The works all been done for you and for what you get it's not terribly expensive.

All you will do is bugger up your gun in an attempt to reinvent the wheel.
 
Last edited:
Would need a second bearing to keep latch rod central and in line.
This second bearing would need to stay in comp tube, which with 95 mm stroke leaves too little room.
The TL kit extends comp tube and shortens stroke with good reason.
 
mattyts said:
Just thinking out loud here and drawing inspiration from the various skirtless pistons available aftermarket for the likes of TXs and Prosports.

Has anyone ever parted off most of the body, leaving behind just the head & first bearing recess that runs in the comp tube, omitting the rear section of the piston? There would be considerable weight savings to be had using only factory parts...

Perhaps the bearing at the piston head would need to be remade to a closer tolerance to keep the piston running central since there'll be no rear bearing & not much support for the spring, or place a delrin disc between the tophat & spring, or have the top hat base oversized to act as a second bearing?
Click to expand...
What kind of weight are you trying to achieve for your piston ?
 
A Tony 22mm set up is close to half the weight of the standard setup. I have some pictures of the two on some scales somewhere, I’ll try to find them. In the meantime, a quick picture of the two…

7C0C095F-DE00-4ACC-891E-EDF0AD1CD9C3.webp


2FBD622D-AC91-4987-94D2-95DCCAE3BFFC.webp
 
Nords said:
A Tony 22mm set up is close to half the weight of the standard setup. I have some pictures of the two on some scales somewhere, I’ll try to find them. In the meantime, a quick picture of the two…

View attachment 227874

View attachment 227875
Click to expand...
if the stroke is kept the same . Lets say 95mm then the swept volume is reduced from 46 odd cc to 36 odd thats errr.... 20 ish % ? reduction in volume .
But its the 380mm/2 vs 490mm/2 frontal area that makes the piston need less mass to do piston stuff.

It's been a while but if the op is going to stick with std stoke ( whassat 95 ish on a mk3 ? ) probably 200 g give or take would be a good starting place .
Take too much off and more spring will be needed .
Where's @Nickg when you need him . He'll have all this stuff off pat .
 
Available space in compression tube is 110 mm.
Front of piston seal to front of rear bearing is 115 mm. When assembled in comp tube there is a 5 mm gap between rear bearing and comp tube.
On a 95mm stroke, anything more than 15 mm back from front of piston seal comes outside comp tube.
This does not leave enough for an effective second bearing that stays within comp tube.
Factory front bearing ring is 3 mm wide, sitting 7 -10 mm back from front of seal.
 
Hmangphilly said:
if the stroke is kept the same . Lets say 95mm then the swept volume is reduced from 46 odd cc to 36 odd thats errr.... 20 ish % ? reduction in volume .
But its the 380mm/2 vs 490mm/2 frontal area that makes the piston need less mass to do piston stuff.

It's been a while but if the op is going to stick with std stoke ( whassat 95 ish on a mk3 ? ) probably 200 g give or take would be a good starting place .
Take too much off and more spring will be needed .
Where's @Nickg when you need him . He'll have all this stuff off pat .
Click to expand...
You have it correct ISH Phil, standard stroke 98 mm 200 grams is about right, you can get that by turning the piston skirt down plenty of meat in the wall, you can get it down as far as 180 grams.
The piston nose won't work as it's too short to offer enough support, so you end up with massive friction, if you support the rod in the guide , ie fixed guide same thing more friction, it's why I left skittles behind a long while back .
A well designed full piston with good bearings and an efficient method of sealing is the way to go .👍
 
Nickg said:
You have it correct ISH Phil, standard stroke 98 mm 200 grams is about right, you can get that by turning the piston skirt down plenty of meat in the wall, you can get it down as far as 180 grams.
The piston nose won't work as it's too short to offer enough support, so you end up with massive friction, if you support the rod in the guide , ie fixed guide same thing more friction, it's why I left skittles behind a long while back .
A well designed full piston with good bearings and an efficient method of sealing is the way to go .👍
Click to expand...

Cheers Nick. It's a Mk2 TX, so 83mm stroke?

Do you recon I can shave off some weight from the piston given it's short stroke, without struggling to make power?
 
200 g ideal at mk 2 stroke,
180 g and 77 mm stroke ( very low recoil/ sight picture movement, but heavy cocking),
if you stay with the standard seal you will need to increase the preload to set the power.
If you use a seal that offers less dynamic friction you can use less spring. Make sure guides aren't tight , it's all about low friction.
 
Last edited:
Nickg said:
200 g ideal at mk 2 stroke,
180 g and 77 mm stroke ( very low recoil/ sight picture movement, but heavy cocking),
if you stay with the standard seal you will need to increase the preload to set the power.
If you use a seal that offers less dynamic friction you can use less spring. Make sure guides aren't tight , it's all about low friction.
Click to expand...
What seal and t.p size would you recommend nick with the 200 gram mk2 piston?
 
Advice should be calibre specific. When a reduced cylinder produces more power in 177 than it does in 22, general assumptions don't always apply.
 
Triggertime said:
What seal and t.p size would you recommend nick with the 200 gram mk2 piston?
Click to expand...
I was assuming,.177. standard port is fine ,I don't use piston seals so can't comment, that would be down to your own experiments. I have always had better results with o rings, x rings , and piston rings than lip / parachute seals , others would disagree no doubt 🙄.
 
You must log in or register to reply here.
Back
Top