Servicing a 70s Mercury - Spring Choice

[CapitalBee]

When I recently rebuilt a mk6 airsporter, I replaced the standard BSA O ring with a smaller section ring. This helped assembly and initial performance as I found the standard O ring was a blinking tight fit. I have some spare I think. If you want one drop me a PM.

[james_stan]

When I recently rebuilt a mk6 airsporter, I replaced the standard BSA O ring with a smaller section ring. This helped assembly and initial performance as I found the standard O ring was a blinking tight fit. I have some spare I think. If you want one drop me a PM.

Thanks - I have some BS212 orings as suggested earlier in this thread but if it turns out too tight I'll be in touch! BS210 was mentioned as a smaller option too.

[look no hands]

Sorry for joining the party late Gents, I've only just seen this thread, this is exactly why I always recommend stripping any new (to you) Airsporter or Mercury/Challenger and replacing the whole lot attached to the front of the piston (unless you know that it's been done already), even if the rifle is cocking and shooting fine, just strip it and see what's going on inside and normally the buffer washer is slowly choking up the insides and as James has found out they can be a right bitch to get the piston out, what you've done so far is normal practice, so don't think you've damaged anything, once it's all out, smooth off the cocking slot inside and out including the rounded hole, polish the piston up and replace the buffer washer and head and use a Meteor O ring as they are slightly smaller, TR Robb does a good head replacement kit with different size O rings, then get intouch with Tinbum to get either a set of guides made up (if your original spring is in good nick) or get a full kit made up as Nick uses HW springs and they are the closest springs you will get to original without having to go Titan, which are very good but will need shortening to fit in the rifle, before reassembling just have a little look at the nut that holds the threaded cup onto the back block isn't loose as if they come loose, then the whole back block will spin and not undo from the cylinder, you will need a very thin walled socket to do it up if it is loose but it's rare that it does come loose but I've had a couple over the years, when putting the piston back in take care not to damage the O ring on the threads that hold the back block in and the cocking slot that you should have smoothed out nicely, I've found putting the back block into a padded vice and pushing the cylinder onto the back block and getting started on the thread that way.

Pete

[james_stan]

Thanks. I can at confirm hat the BS212 (21.82 ID 28.88 OD is too tight at least in combination with Chamber's alloy piston as you push it through the threaded section it bucks up at the slotso I cut it in the end to get it off. My digital verniers are out of commission at present but the old verniers measure an ID of 22.2 ish on the piston ring slot and about 27.4mm on the outside of the piston. With this in mind I guess we should be aiming for a BS 211 (20.22 ID 27.28 OD) or metric might be better at (21 ID 28 OD). @ CapitalB ee do you know what your size is? These things are easy and cheap to source on - once you know what works!

[look no hands]

Thanks. I can at confirm hat the BS212 (21.82 ID 28.88 OD is too tight at least in combination with Chamber's alloy piston as you push it through the threaded section it bucks up at the slotso I cut it in the end to get it off. My digital verniers are out of commission at present but the old verniers measure an ID of 22.2 ish on the piston ring slot and about 27.4mm on the outside of the piston. With this in mind I guess we should be aiming for a BS 211 (20.22 ID 27.28 OD) or metric might be better at (21 ID 28 OD). @ CapitalB ee do you know what your size is? These things are easy and cheap to source on - once you know what works!

You have to make sure you have the right shaw with the O ring, otherwise it will destroy itself after a short time in the cylinder.

Pete

[james_stan]

Hi Pete

'Shaw' ?

Cheers

james

[Shed tuner]

Hi Pete

'Shaw' ?

Cheers

james

"Sure" rating, e.g. 90 instead of 70. i.e. something a bit tough, but I've never found it that critical. I'd go with Pete's advive though, he's rebuilt more than most of us