HW 97K Variable Power

[W&SP]

I bought a nice 2nd hand 97k .177 six months ago (off this forum) which had been tuned - looks like a V-Mach kit.

When I got it home & chrono'd it, it was over the limit. So I stripped it down and removed about 6mm of pre-compression washers (3 washers), cleaned & re-lubed.

Power then went way, way down to around 7-8 lbs sq ft! So I re-installed the washers one by one. It took all 3 washers / 6mm to get to around 11.5 lbs. So I then left it - job done.

I re-chono'd the rifle today to find that it was once again over the limit by 1-2 lbs. So I immediately stripped it and once again removed the 6mm of washers, cleaned and re-lubed.

Power is now once again down to average 7 lbs sq ft.

This is my 1st HW97 but not my first strip/clean/lube so I was wondering what might be causing this?

Could it be dieseling? After a few shots today there was no 'smoke' coming out the barrel. And I've not noticed smoke or smell when using the rifle since my initial strip down.

I know they can creep after a while but it has not been used excessively over the 6 months of ownership - a few tins

Or is there another likely cause?

Thanks in advance!

[Mark_WBA]

Are the washers piston end or spring end.

Are the seals OK ?

[yorkiets]

Loading gate / breech sealing ok?

[lensman57]

I bought a nice 2nd hand 97k .177 six months ago (off this forum) which had been tuned - looks like a V-Mach kit.

When I got it home & chrono'd it, it was over the limit. So I stripped it down and removed about 6mm of pre-compression washers (3 washers), cleaned & re-lubed.

Power then went way, way down to around 7-8 lbs sq ft! So I re-installed the washers one by one. It took all 3 washers / 6mm to get to around 11.5 lbs. So I then left it - job done.

I re-chono'd the rifle today to find that it was once again over the limit by 1-2 lbs. So I immediately stripped it and once again removed the 6mm of washers, cleaned and re-lubed.

Power is now once again down to average 7 lbs sq ft.

This is my 1st HW97 but not my first strip/clean/lube so I was wondering what might be causing this?

Could it be dieseling? After a few shots today there was no 'smoke' coming out the barrel. And I've not noticed smoke or smell when using the rifle since my initial strip down.

I know they can creep after a while but it has not been used excessively over the 6 months of ownership - a few tins

Or is there another likely cause?

Thanks in advance!

Probably lubrication is getting past the seal when the gun is left unused and causes slight dieseling. I would try and clean the whole lot off the present lube and relube very sparingly to see what the gun does. You may need a new seal. Probably the ex owner had taken too much off the piston seal.

A.G

[W&SP]

Thanks all!

Washers removed were all piston end. Is that significant?

I thought the piston seal was OK fit but will double check.

Same regards breech.

I relubed much more sparingly this time.

[tinbum]

If the piston seal is tight it'll drop power dramatically with preload removed, it'll then start to bed in and rise as its used. Check the fit to the comp tube.

[rovercoupe]

Does the spring guide fit tight in the cylinder or does it move freely? I had no end of trouble untill i ground the lip down a touch and it was constantly firing bang on after that.

[W&SP]

Thanks - a few good pointers to follow!

[W&SP]

Had chance to strip the rifle again today.

Breech seal looks OK but can try replacing it (or fliping it).

The piston seal looks very much like a V-Mach and is a fairly snug fit. It moves OK but does need a bit of effort. Should it be looser?

I've read that V-Mach seals tend to be a tight fit & they say leave them that way.

Seal has been in place for a few years so shouldn't it have bedded in by now?

Also does it matter where the washers are - piston or spring end?

[Mark_WBA]

Washers In the piston add weight to the piston which in turn needs more power to shift it.

Washers / power bands - at the guide end increase preload on the spring

Seals should be a snugg fit but not to snugg. IMO the weihrauch seal is hard to beat.

[CantankerousOne]

Thanks all!

Washers removed were all piston end. Is that significant?

I thought the piston seal was OK fit but will double check.

Same regards breech.

I relubed much more sparingly this time.

My 97 had a similar problem with fluctuating power levels - strip, degrease and a very sparing relube cured it. I think it must have been dieseling.

[W&SP]

Thanks all.

I suspected dieseling could be the culprit. Need to test with less lube.

My previous question was that if the seal is a few years old, looking OK and a snug fit shouldn't it have bedded in after a few year's use?

Just trying to rule things out and get back to legal limit shooting.

[W&SP]

Washers In the piston add weight to the piston which in turn needs more power to shift it.

Washers / power bands - at the guide end increase preload on the spring

Seals should be a snugg fit but not to snugg. IMO the weihrauch seal is hard to beat.

Is there any benefit of increasing weight to piston?

[bozzer]

Like Tinbum says ... Power down to about 7 or 8 fp with a V kit in is classic tight piston seal robbing all the power. So first job is getting that right. You should be able to grip the back of the rod with finger and thumb and easily slide the piston in and out of the comp tube. If it's just falling on it's own weigh then that's too slack for me. If you are having to put some effort into pushing it in and pulling it out then it's way too tight.

Have you tested the end of the comp tube? Rubber gloved thumb over Transfer Port ... push in piston ... should hit a wall of air resistance etc.

How tight are the Top Hat and Rear spring guides? They should slide in and out easily. Some like the Top Hat to be tighter. If they are tight and you have to try hard to get them in and out of the spring then they are too tight.

What's the state of the spring? Look down it's length ... is it straight with all the coils sitting in a straight line with no coils sticking out of line?

How many coils on the spring? Where is the end of the spring with it re assembled before you screw on the back block with respect to the main tube?

You mention that the seal should have run in if it's been fitted years ago. That depends on how much it's been shot or what the seller did to it just before selling it to you. Maybe they put a new seal in and it needs sizing?

Keep us updated please.

[PhatMan]

Hello to All,

When I had some work done on my TX200 by Mr. Pope, he asked that I send him the compression tube so that he could fit the V-Mach piston seal.

Talking to him later, he stressed the need to fit V-Mach piston seals - you don't just plonk them in and get best results.

So it looks like these V-Mach seals do need fitting for best results.

Have fun & a good Sunday

Best regards

Russ