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!

[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.