HW35 piston change

[CJBD]

I have changed the piston on my early HW35 from the leather sealed version to the synthetic sealed version.The rifle will now not cock.The piston rod
on the new piston is slightly shorter than the original.I have spoken to Nick at TINBUM(very helpful),He pointed me to the forum and in particular to 'T20'.
Has any one else made this mod' ? Any help would be helpful.

[Shed tuner]

the piston will have to come back further into the end block in order to cock - this means the stroke is a bit longer, which is a good thing on a 35.

If it won't cock, I'd be suspicious that something is stopping the piston from going all the way back, e.g. the mainspring becoming coilbound (either 'cos it is now too long, or you have washers in there), or a washer / spacer on the rear guide that the piston skirt is butting up against. Final option is the spring guide itself is bottoming out on the inside face of the piston, or on a top hat (if fitted).

Easy way to test is to strip the gun, remove the spring, and shove the piston into the trigger block, making sure it cocks (it will need a firm shove, and can be released by "firing" the trigger).

Then try the same with the guuide / TH / any washers in place.

If they work, there's only the spring left to blame.

[tinbum]

the piston will have to come back further into the end block in order to cock - this means the stroke is a bit longer, which is a good thing on a 35.

If it won't cock, I'd be suspicious that something is stopping the piston from going all the way back, e.g. the mainspring becoming coilbound (either 'cos it is now too long, or you have washers in there), or a washer / spacer on the rear guide that the piston skirt is butting up against. Final option is the spring guide itself is bottoming out on the inside face of the piston, or on a top hat (if fitted).

Easy way to test is to strip the gun, remove the spring, and shove the piston into the trigger block, making sure it cocks (it will need a firm shove, and can be released by "firing" the trigger).

Then try the same with the guuide / TH / any washers in place.

If they work, there's only the spring left to blame.

I think we've looked at everything with this one Jon, even reverting to the original guide with no top hat, it just won't cock!

As you know, the 35 aint my forté, so I advised Colin ask some grown-ups!

[Shed tuner]

I think we've looked at everything with this one Jon, even reverting to the original guide with no top hat, it just won't cock!

will it cock with no guide at all ? (wondering if the rod is slightly off centre or binding in the guide ?)

If it won't cock with just piston into block, there is only the rod / profile left... unless of course you muppets cocked the trigger when refitting and forgot to "fire" it before testing

In fact, have you testing cocking and firing the trigger (using a screwdriver to push from near the main rear stud fitting) ? - maybe a trigger issue as Mick suggested above

[tinbum]

.. unless of course you muppets cocked the trigger when refitting and forgot to "fire" it before testing

I would like to point out I am many hundreds of miles from the gun!

[landymick]

As Mick has said it should work correctly with just the swap if nothing else has been changed.

Try loosening the trigger guard screws slightly & give it a try.

[NickG]

I would like to point out I am many hundreds of miles from the gun!

Did JB just call you a Muppet Nick ! , whatever happened to treating your fellow Tuner / poster with the respect they deserve ?
Manners have obviously gone out of the window

[T 20]

I have changed the piston on my early HW35 from the leather sealed version to the synthetic sealed version.The rifle will now not cock.The piston rod
on the new piston is slightly shorter than the original.I have spoken to Nick at TINBUM(very helpful),He pointed me to the forum and in particular to 'T20'.
Has any one else made this mod' ? Any help would be helpful.

Very strange, the pistons are interchangeable.



The earlier leather sealed piston has 35 mm of sear rod protruding out the back of the piston with a total rod length of 130 mm.

The later synthetic sealed HW35 has 30mm of sear rod protruding out the back of the piston with a total rod length of 135 mm.


I suspect your gun is either going coilbound on the spring or perhaps your guide and top hat are too long.

As a simple check, remove the spring from the gun but leave the guide and top hat in there and see if the gun will cock.

If the gun won't cock, remove the guide and try again.

If the gun still fails to cock, you could have a trigger fault.


If all else fails, remove the piston and then push the latch rod into the trigger block to see if the trigger latches.


Edit :- note to self --- must type faster than JB



All the best Mick