Spare parts replacement

[moulindu]

Hi
What is the general opinion for changing/replacing of barrel seals, piston seal & piston rear & front bearings?
I think to change all those wearing parts together at the same time can produce better result as of now my TX is giving extreme spread of more than 30fps.
I read somewhere that changing of outer barrel seal is sufficient as the inner seal is for supporting/cushioning the outer one.
I am planning to change those internals & see if that could solve that problem.
Thanks Moulindu

[Sake-san]

Hi Moulindu
Is the spread of 30fps with weighed pellets?, I would start by just replacing the breach seals, they cost peanuts so do both together as the lower one will also become compressed after a time. If the piston seal looks visually ok and you have good compression then it should be fine, their useful life is typically tens of thousands of shots.
As to what is normal... that depends upon a number of factors and variables including but, not only the number of shots, age, the type of seals used, the fit of the seals, the power level and stroke of the gun, the type, quality and quantity of lubrication, the absence or otherwise of dieseling, temperature exposure, weight of pellets being used, trueness of the compression tube, etc.
The delrin guides usually have a very long life but, check them (especially rear one) for score marks / surface cuts which can indicate that some deburing of the action would be beneficial.
Hope that helps

[Timmytree]

As Sake says, all can have an effect but on my PS I found recently that inconsistency was down to the piston seal, a new seal cured the problem instantly. Preload too low can have an effect, breech seals I change regularly anyway. I still believe that too little grease at the spring guide end can cause a problem. Think of the spring in a car suspension, it needs a damper of sorts to control the movement, I believe springer powerplants need grease and a tighter seal to do the same job.

[moulindu]

First of all Merry Christmas to all fellow members.

Is the spread of 30fps with weighed pellets?

No the pellets aren't weighed, only sorted (left out deformed pellets).

I would start by just replacing the breach seals, they cost peanuts so do both together as the lower one will also become compressed after a time

Ok i will change both breech seals.

As to what is normal... that depends upon a number of factors and variables including but, not only the number of shots, age, the type of seals used, the fit of the seals, the power level and stroke of the gun, the type, quality and quantity of lubrication, the absence or otherwise of dieseling, temperature exposure, weight of pellets being used, trueness of the compression tube, etc.

1) Around 5000 shots fired
2) AA stock seal
3) While pulling the piston out of the transfer port there is some resistance, & on closing the transfer port with finger the piston doesnt slides down.
4) Power level is 13fpe at muzzle after putting derlin kit
4) Stroke of the gun is 100mm, i guess for standard MKIII, didnt do any alteration in stroke length.
5) There is no dieseling & its now operating at around 10C
6) I am using JSB Exact 8.44 grn pellets
7) I have no idea about trueness of compession tube.

As Sake says, all can have an effect but on my PS I found recently that inconsistency was down to the piston seal, a new seal cured the problem instantly. Preload too low can have an effect,

Yes TT I am thinking of changing the piton seal as well to check if the problem still persist then can think off some other issues. The derlin kit i used didnt put any power washers as this power is too much for my liking.

I still believe that too little grease at the spring guide end can cause a problem. Think of the spring in a car suspension, it needs a damper of sorts to control the movement, I believe springer powerplants need grease and a tighter seal to do the same job.

I use Jim Maccari tar for dampening the spring & at tophat & rear guide end i use Jim Maccari moly to reduce friction.
Thanks guys for input, i ll put those input into affect & see for improvement.
Regards Moulindu

[moulindu]

I have installed new breech seals, piston seal, piston rear & front piston bearings, but I have also replaced the derlin top hat/ piston weight with stock metallic piston weight. Now the current setup has changed the feel of recoil, though its snappier but it held the sight picture throughout as Sakesan suggested & its producing 767 fps at 11.2fps but still getting spread of 20 fps. I am guessing that the heavier piston weight has made recoil in a linear pattern i.e towards shoulder whereas that derlin piston weight made lesser recoil but on transverse direction for longer duration. After zeroing at 14 yds I got 2, 5 shot groups of 8mm & 10mm. Now the feel is what I am used to & going to stick to that, but felt cocking effort is more compared to earlier experience, is it because of new piston seals & piston bearings?
Thanks Moulindu

[KeithS]

Is the spring okay that might have issues ...

[pelletcaster]

4) Stroke of the gun is 100mm, i guess for standard MKIII, didnt do any alteration in stroke length.

???
To my knowledge the stroke of this AG is 86 mm, compression tube dia 25 mm thus giving a swept volume of 42,2 ccm.
TP length 9,8 mm, dia 3,75 mm thus swept volume 0,108 ccm.
Resulting in SCR (static compression ratio) of 42,2 divided by 0,108 = 390:1
More or less.

Can anybody enlighten me please?

I know about short stroking but is it possible to long stroke this AG to 100 mm or any other (maximum) stroke length?

Thanks a lot.

[Sake-san]

I have installed new breech seals, piston seal, piston rear & front piston bearings, but I have also replaced the derlin top hat/ piston weight with stock metallic piston weight. Now the current setup has changed the feel of recoil, though its snappier but it held the sight picture throughout as Sakesan suggested & its producing 767 fps at 11.2fps but still getting spread of 20 fps. I am guessing that the heavier piston weight has made recoil in a linear pattern i.e towards shoulder whereas that derlin piston weight made lesser recoil but on transverse direction for longer duration. After zeroing at 14 yds I got 2, 5 shot groups of 8mm & 10mm. Now the feel is what I am used to & going to stick to that, but felt cocking effort is more compared to earlier experience, is it because of new piston seals & piston bearings?
Thanks Moulindu

Just stick with it, cocking pressure increase maybe due to deeper (more pre-load) top hat vs your delrin one. Stop the fettling and get to know it intimately, the sweet spot for target shooting is generally around 11.2 ft/lbs with a TX.

[FPoole]

4) Stroke of the gun is 100mm, i guess for standard MKIII, didnt do any alteration in stroke length.

???
To my knowledge the stroke of this AG is 86 mm, compression tube dia 25 mm thus giving a swept volume of 42,2 ccm.
TP length 9,8 mm, dia 3,75 mm thus swept volume 0,108 ccm.
Resulting in SCR (static compression ratio) of 42,2 divided by 0,108 = 390:1
More or less.

Can anybody enlighten me please?

I know about short stroking but is it possible to long stroke this AG to 100 mm or any other (maximum) stroke length?

Thanks a lot.

Standard MarkIII is 98mm stroke. Standard MarkI and MarkII is 84mm stroke. There was also an FAC piston in the MarkII that was 93mm stroke.

[pelletcaster]

4) Stroke of the gun is 100mm, i guess for standard MKIII, didnt do any alteration in stroke length.

???
To my knowledge the stroke of this AG is 86 mm, compression tube dia 25 mm thus giving a swept volume of 42,2 ccm.
TP length 9,8 mm, dia 3,75 mm thus swept volume 0,108 ccm.
Resulting in SCR (static compression ratio) of 42,2 divided by 0,108 = 390:1
More or less.

Can anybody enlighten me please?

I know about short stroking but is it possible to long stroke this AG to 100 mm or any other (maximum) stroke length?

Thanks a lot.

Standard MarkIII is 98mm stroke. Standard MarkI and MarkII is 84mm stroke. There was also an FAC piston in the MarkII that was 93mm stroke.

Very interesting - thanks a lot.