O-Rings for BSA Mercury and Airsporter

[MattyBoy]

Hi all

Having rebuilt several Airsporters and Mercurys I have come up against a common problem - the "standard" O-Ring from Chambers are always too tight in the cylinder and rob the gun of power.

I have just rebuilt my .22 Challenger and with the standard O-Ring she was putting out 9 ft lb.

I then replaced the O-Ring with one supplied for the Meteor and this was a comfortable fit and gave 11.5 ft lb

Has anyone else had this experience? Is there any problem with doing this? Too loose O-Ring causing piston slam or similar?

I rebuilt my .177 MK 1 Mercury a few months ago and it's only giving 8 ft lb. I am going to replace the O-Ring in this one for a meteor one and see what happens.

I guess if I put 500 pellets through with the original larger O-Ring the power would gradually go up, but I seem to have found a better way of getting full power immediately.

Thoughts?

Thanks
Matty

[Hsing-ee]

Yes, I rebuilt a Mercury-S a few years ago, put in a piston liner and a Maccari spring, very smooth cocking and nice 'thud' on firing, but only 8 ft/lbs! I am sure I did not knick the 'O' ring as it went in, but it was a very tight fit. I sold the rifle on as I was having a purge so I didn't shoot it much. As I remember from the 1970s though, BSAs had a very long running in period and the best thing to do is to get a couple of thousand pellets through it, the ring beds in and the power creeps up to where it should be. The rifle then is very consistent for years, and you only need to put in a mainspring from time to time when the power drops off, no need to take the piston out.

[RichardH]

Or cut the groove deeper for the ring

[gedfinn 2]

Hi all

Having rebuilt several Airsporters and Mercurys I have come up against a common problem - the "standard" O-Ring from Chambers are always too tight in the cylinder and rob the gun of power.

I have just rebuilt my .22 Challenger and with the standard O-Ring she was putting out 9 ft lb.

I then replaced the O-Ring with one supplied for the Meteor and this was a comfortable fit and gave 11.5 ft lb

Has anyone else had this experience? Is there any problem with doing this? Too loose O-Ring causing piston slam or similar?

I rebuilt my .177 MK 1 Mercury a few months ago and it's only giving 8 ft lb. I am going to replace the O-Ring in this one for a meteor one and see what happens.

I guess if I put 500 pellets through with the original larger O-Ring the power would gradually go up, but I seem to have found a better way of getting full power immediately.

Thoughts?

Thanks
Matty

Hi Matty, ( Sorry its me again ! )
the piston diameter of the Meteor is 25 mm & The Mercury is 28mm < It just fit ! ( Well it will if stretched, But last ! )
To get decent power out of a Mercury, You need a " Heavyweight "
Steel piston head .
The O rings come in Metric & Imperial , Buy a box & try both sizes , They can make 12 Fpe without a problem , But it takes a decent spring & That heavyweight piston head,
As was said above, The groove in the piston head can be machined out on a lathe to give clearance !

Tight O rings just cut it !

Having said that, They can & do give good power with a long life , When fitted correctly !
All the best, Ged.

[richywilk]

Hi Matty,
An interesting thread, I had a conversion done on a Mercury by John Bowkett back in the mid 80s, it's a shame he's not working on springers now as his own design piston head was so efficient he had to reduce
the standard main spring to keep it under the legal limit.
I remember him telling me it took 500 pellets to run in and never lube the piston head,I've got to say it was one of the best rifles I've ever owned I wish I never sold it.
Richy

[MattyBoy]

Hi Matty, ( Sorry its me again ! )
the piston diameter of the Meteor is 25 mm & The Mercury is 28mm < It just fit ! ( Well it will if stretched, But last ! )
To get decent power out of a Mercury, You need a " Heavyweight "
Steel piston head .
The O rings come in Metric & Imperial , Buy a box & try both sizes , They can make 12 Fpe without a problem , But it takes a decent spring & That heavyweight piston head,
As was said above, The groove in the piston head can be machined out on a lathe to give clearance !

Tight O rings just cut it !

Having said that, They can & do give good power with a long life , When fitted correctly !
All the best, Ged.

Interestingly my Mercury 1973 and my Airsporter S 1990 both have nylon piston heads

The 1986 Challenger I just got has an ally piston head

No steel in these...

Perhaps I can get hold of one or get one made in Brass?

I took the .177 Mercury apart again today to check the O-ring clearance/tightness and actually it was fine. (The A/Sporter S one was very tigfht and very low power as a result).

The Mercury has a standard OEM spring sourced from Ormicron and preload is about 2 inches.

It only gives 7.3 ftlb

Cheers
Matty

[MattyBoy]

Well I have just taken out the OEM spring in the Mercury and fitted a TITAN XS 01

I was just able to get the back block in - 4 inches of sprig sticking out of cylinder

Power only up from 7.3 to 7.9 and recoil dreadful.

Bollos