Piston scuff marks

[rg627]

Hi

My hw99 has developed some scuff marks on the metal piston. I assume it's from metal to metal contact, is this anything to be wary of?

I stripped it down to degrease as it was dieseling a bit, i then saw the marks and raised my concerns.

Is this common in hw break barrels?

Thanks

[tinbum]

It happens all the time and comes from the cocking stroke, not firing. Put the piston into a cordless drill by the latchrod and spin it up gently with some medium wet and dry til the witness marks have gone, then some fine, then fine with oil. Finish with Autosol or similar, relube carefully, rebuild and ignore for next 5,000 shots.

[Hsing-ee]

I found that the REAR of the compression tube (not the bit that is actually involved in the chamber) is often rough as a badger's arse that has been roughened with badger-paper of the coarsest grade. You can smooth this down with a thick dowel and some fine emery paper, or with a cylinder hone if you are brave and don't get the hones involved with the cocking slot.

Then follow Mr Bum's advice.

[rg627]

Ok thanks

So if I polish the piston and hone the rear of the cylinder it should prevent it.

Funny you say the cooking action, it does sound a little gritty if that makes sense.

Am I right in assuming that as long as the piston seal and bore are a good fit, the rear doesn't matter if a tad of metal has been removed/ honed?

I am going to use bisley gun grease, is this still a good option for rebuild? I'll do a smidge on the piston seal and a smidge in the rear of the piston. None on the spring. Is this still the agreed way to re lube?

[TonyL]

The Bisley Gun Grease will do fine.

A VERY small amount (hardly visible) on the edge of the seal - none in front.

I'd use a fairly generous amount on the rear inch or so of the piston, rubbed in. Then, with the piston pushed fully forwards, before you fit the spring, apply some more of the grease to the inside of the cylinder, around the circumference, behind the piston, using a stiff plastic straw or similar.

Depending on guide fit, I usually DO grease the spring. A moderate amount "worked in" around the whole of the inside and outside and also the spring ends.

[junglie]

I've found maxigrip fitted bsa'a a bugger for this, careful de-burring of the fixing slots & the cocking slot stops it happening again.

[robs5230]

I've had this before on a 95. I reckon its down to the rifle being a little oversprung and the rear of the piston tipping upwards on cocking.

And in the case of this rifle it was me that over sprung it upon fitting a delrin guide kit. Very smooth before I stripped it and picking up on the rear of the piston within a few shots of fitting the kit. Easily sorted but left marks in the top of the cylinder within a few shots.
The spring in the rifle at the time was the 77 spring that they now seem to fit to all rifles. A very sloppy fit in the piston which I dont think helped. That was removed and a 16j 95 spring installed.

Dress off the rear of the piston as said, spinning it up in a drill or on a lathe. Make sure you round off the very back edge too.
I then use moly paste on the rear bearing which I find stays better. You may also want to check inside the cylinder. If the piston has marked , the cylinder may well have marked more. This will also need dressing out and some moly paste applied in that area.
If not "fixed", I'd make sure all the other noted areas are attended to on the 99 too to prevent galling.

[noz1]

When spinning a piston by the latch rod, do not use a fast speed as it is possible for it to flail, bending the latch rod. A friend of mine has done this.
I use my lathe and I use a tailstock centre to prevent this occurring.

[robs5230]

Ok thanks

So if I polish the piston and hone the rear of the cylinder it should prevent it.

Funny you say the cooking action, it does sound a little gritty if that makes sense.

Am I right in assuming that as long as the piston seal and bore are a good fit, the rear doesn't matter if a tad of metal has been removed/ honed?

I am going to use bisley gun grease, is this still a good option for rebuild? I'll do a smidge on the piston seal and a smidge in the rear of the piston. None on the spring. Is this still the agreed way to re lube?

Cant see any point in lubing the seal unless its been sized. The smooth sides of the standard unsized seal will not retain lube and you'll end up with dieselling to some extent.
Some lube will be needed on the guide and top hat, the rest of the spring can remain dry

[rg627]

Ok cheers

Interesting point about the no grease on piston seal, I have not heard that before but may try.

I shall have a look at the cylinder to see if there's corresponding marks.

Ideally I don't want any dieseling at all, I think it originally dieseled hence hence the poor consistency in muzzle velocity.

Seemed to follow a string if consistent shots and then every few through in a much higher or lower number.

[venoman]

The problem is that Weihrauch pistons are very soft , one cure is to fit a V-Mach V-Glide kit . If you dont want to spend that much rebuild it putting Rocol dry moly paste on the rear of the piston . Rub a light film of moly grease to the side of the piston seal enter it into the cylinder , then rub Rocol onto the rear of the piston push it fully into the cylinder and then rub some onto the wall of the cylinder behind the piston.

[rg627]

Thanks guys

I will try that on the next rebuild.


On a side note, I watched a t. R Robb video of assembly. He reamed the transfer port.

Has anyone tried this? He sells port reamers. I'd like to get shot to shot consistency and good as I can. Power increase isn't too much of a concern to me, 10-11 ftlbs is fine.

I've not seen people talk about reaming transfer ports for years.

[TonyL]

Think I'd be leaving the transfer port alone.

[venoman]

Thanks guys

I will try that on the next rebuild.


On a side note, I watched a t. R Robb video of assembly. He reamed the transfer port.

Has anyone tried this? He sells port reamers. I'd like to get shot to shot consistency and good as I can. Power increase isn't too much of a concern to me, 10-11 ftlbs is fine.

I've not seen people talk about reaming transfer ports for years.

When i tune rifles i have a tool to countersink the transfer port , this dont make the port bigger .

[rg627]

Yes, that sounds like the tool t r Robb used, on a long rod