Hw90/fenman

[sarfarm]

This may have been discussed before but I have not found anything.
Both these guns share the same system but there is a considerable difference in their operation,the fenman in sub 12 operates at about 600psi,the 90 operates at around 300,yet even with its short barrel the fenman requires less effort to cock,anyone got any ideas as to why this is the case.

[robs5230]

This may have been discussed before but I have not found anything.
Both these guns share the same system but there is a considerable difference in their operation,the fenman in sub 12 operates at about 600psi,the 90 operates at around 300,yet even with its short barrel the fenman requires less effort to cock,anyone got any ideas as to why this is the case.

They share a similar system but not the same. The HW90 has the ram design developed in conjunction with HW.
Theres a lot of components inside the fenman ram and less in the 90 ram. The 90 is also a bigger diameter piston I believe whereas my fenman was 27mm. I wrote a stripdown guide for a fenman a few years ago. Very different kettle of fish to the 90

[bighit]

Im sure the stroke is longer on the HW90 too .

100mm or 110mm from some sources for the Hw90 and 66mm for the Theoben Fenman

Post here about the Theoben

"The stroke of the piston on a 12 ft lbs theoben gas ram is 2.6 inches he or not. the diameter of the (dummy piston) or gas ram on the he model is 1/3 of that of the earlier one and the pressure goes up from 300 psi non HE to 750 psi HE. to achieve Fac velocity the stroke is increased to3.2 inches the eliminator has a stroke of 3.7 inches all Theoben's after TB 6000 are HE"

[robs5230]

Im sure the stroke is longer on the HW90 too .

100mm or 110mm from some sources for the Hw90 and 66mm for the Theoben Fenman

Post here about the Theoben

"The stroke of the piston on a 12 ft lbs theoben gas ram is 2.6 inches he or not. the diameter of the (dummy piston) or gas ram on the he model is 1/3 of that of the earlier one and the pressure goes up from 300 psi non HE to 750 psi HE. to achieve Fac velocity the stroke is increased to3.2 inches the eliminator has a stroke of 3.7 inches all Theoben's after TB 6000 are HE"

The one I rebuilt and wrote the stripdown guide for was a HE fenman. I did check back to see what the pressure was and i recommended a start pressure of 600PSI on rebuild so from that I assumed the OP was also talking about a HE model.

The internal volumes of the rams are very different as you've also highlighted. So are the cocking linkages.
The design of the fenman cocking linkage will affect ease of cocking so the barrel length comparison would be irrelevant.

[Shed tuner]

Im sure the stroke is longer on the HW90 too .

100mm or 110mm from some sources for the Hw90 and 66mm for the Theoben Fenman

Post here about the Theoben

"The stroke of the piston on a 12 ft lbs theoben gas ram is 2.6 inches he or not. the diameter of the (dummy piston) or gas ram on the he model is 1/3 of that of the earlier one and the pressure goes up from 300 psi non HE to 750 psi HE. to achieve Fac velocity the stroke is increased to3.2 inches the eliminator has a stroke of 3.7 inches all Theoben's after TB 6000 are HE"

The 90 is only long stroked in FAC format. regular stoke is ~80mm.

But yeah, the guns are so completely different, there is no logic comparing. It's like saying why is an airsporter spring tougher than an HW57 spring. And 30mm HW bore vs 27mm Theo has a big effect too.

[Blackrider]

Apart from the technicalities, I know which I'd rather carrying/shoot in the field !

[sarfarm]

They share a similar system but not the same. The HW90 has the ram design developed in conjunction with HW.
Theres a lot of components inside the fenman ram and less in the 90 ram. The 90 is also a bigger diameter piston I believe whereas my fenman was 27mm. I wrote a stripdown guide for a fenman a few years ago. Very different kettle of fish to the 90

Your stripdown of the Fenman was a great help when I rebuilt mine.
From my stripdown of both guns the system seems the same the overall construction differs and I believe the stroke is different.

[sarfarm]

The one I rebuilt and wrote the stripdown guide for was a HE fenman. I did check back to see what the pressure was and i recommended a start pressure of 600PSI on rebuild so from that I assumed the OP was also talking about a HE model.

The internal volumes of the rams are very different as you've also highlighted. So are the cocking linkages.
The design of the fenman cocking linkage will affect ease of cocking so the barrel length comparison would be irrelevant.

Yes mine was an HE and I started at 600psi and lowered to suit 11.4ft/lbs

[sarfarm]

Apart from the technicalities, I know which I'd rather carrying/shoot in the field !

Yes I will agree with that but the 90 is overall an excellent gun,my idea was to trim some weight off as per the Fenman with a nice short barrel but perhaps I will just stick with my Fenman for field use.

[robs5230]

Yes I will agree with that but the 90 is overall an excellent gun,my idea was to trim some weight off as per the Fenman with a nice short barrel but perhaps I will just stick with my Fenman for field use.

The best of both worlds would be the 90 with a carbine barrel and a CS stock I reckon.
I'd love to love the fenman, just hate the trigger. I find the 90 a little more civilised

[robs5230]

Your stripdown of the Fenman was a great help when I rebuilt mine.
From my stripdown of both guns the system seems the same the overall construction differs and I believe the stroke is different.

Yep you're right with the construction. All manner of bits and pieces in my fenman where the 90 seems rather simpler.

[robs5230]

Yes mine was an HE and I started at 600psi and lowered to suit 11.4ft/lbs

Yeah the 600 was a ball park figure that Phil Russell asked me to give.

[bighit]

The 90 is only long stroked in FAC format. regular stoke is ~80mm.

But yeah, the guns are so completely different, there is no logic comparing. It's like saying why is an airsporter spring tougher than an HW57 spring. And 30mm HW bore vs 27mm Theo has a big effect too.

what about the 31mm bore theobens or has knibbs made a mistake ?

O.D. - 31.3mm
http://www.airgunspares.com/store/pr...o%3A-TH101031/

And
Piston Crown 31.4mm wide
http://www.airgunspares.com/store/pr...o%3A-TH101034/

[robs5230]

what about the 31mm bore theobens or has knibbs made a mistake ?

O.D. - 31.3mm
http://www.airgunspares.com/store/pr...o%3A-TH101031/

And
Piston Crown 31.4mm wide
http://www.airgunspares.com/store/pr...o%3A-TH101034/

The trouble with the theoben rammers in general and definitely the fenman, was that they were in a constant state of R and D during the whole production. Varying internals were used.
I had a lot of conversations with Darren Godfrey at Impact (ex theoben staff) during my rebuild. When I explained my internals he said, "oh you have one of those then" with a chuckle.
The ones quoted by Knibbs may be a more common size. I can only comment on mine which was an early HE.

As for 31mm diameter, I'd personally doubt that for a fenman, I think they went to 28 after 27. 31 maybe for the eliminator but I dont know for sure. A HW80 is only 30mm

I'd be extremely wary of buying any parts unless you have the old ones in your hand as a reference. Likewise, I've bought schraders from Knibbs who listed as what I needed only to find they were the wrong thread. All mentioned in my write up.

[bighit]

The trouble with the theoben rammers in general and definitely the fenman, was that they were in a constant state of R and D during the whole production. Varying internals were used.
I had a lot of conversations with Darren Godfrey at Impact (ex theoben staff) during my rebuild. When I explained my internals he said, "oh you have one of those then" with a chuckle.
The ones quoted by Knibbs may be a more common size. I can only comment on mine which was an early HE.

As for 31mm diameter, I'd personally doubt that for a fenman, I think they went to 28 after 27. 31 maybe for the eliminator but I dont know for sure. A HW80 is only 30mm

I'd be extremely wary of buying any parts unless you have the old ones in your hand as a reference. Likewise, I've bought schraders from Knibbs who listed as what I needed only to find they were the wrong thread. All mentioned in my write up.

I remember this came up before and the post is here http://www.airgunbbs.com/showthread....he-HW90-s-turn post 35


And they are the only sizes of crowns/seals i can find online . Pity Ben Taylor was not on the forum to confirm the queries.