Servicing a 70s Mercury - Spring Choice

[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

[look no hands]

"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

I just realised I said shaw and it should be shore, I couldn't remember how to spell it when I replied this morning, just woken up and was a bit dopey, as I said (and others) I just use the Meteor size O ring now as they don't seem as tight in the bore, the cylinder threads can be a bit of a pain sometimes when getting the piston back in, when I did the parachute seal conversion (for the life of me I can't remember which rifle in my collection has it in now) I had to get some very thin delrin sheet and wrap it round the greased up piston head and push it in that way to avoid the threads.

Pete

[Mr. Gen]

I got fed up with messing with airsporters and mercuries ages ago and had some steel piston heads made up, they take a single o ring and are half the size of the original nylon head so add a little more swept volume as well as the weight - gets the power up easily. you have to extend the cocking slot by a few mm as the piston rests a little further forward but they are an excellent mod, I prefer them to alloy heads.

[Shed tuner]

I just realised I said shaw

Yeah, I just woke up too when I said "sure"

[junglie]

i tried softer shore rated ones in mine the correct size & slightly smaller same as the meteor, lasted a few shots before failing.Maybe I was unlucky with cheap o-rings but I always use the correct ones now & no more problems. Only saying as the're my least favorite rifles to strip because of that curved end block & fine thread to engage on re-assembly.

[james_stan]

Well I never - I've bought a fair few number of o-rings for motorcycle repairs in the past and never encountered 'Shore rating'. Just bought standard nitrile rings. Every day a school day eh? So looks like meteor ring it is. Is the cylinder much smaller on a Meteor?

Cheers

Jams

[look no hands]

Well I never - I've bought a fair few number of o-rings for motorcycle repairs in the past and never encountered 'Shore rating'. Just bought standard nitrile rings. Every day a school day eh? So looks like meteor ring it is. Is the cylinder much smaller on a Meteor?

Cheers

Jams

I believe they are 25mm bore (I know the later Gamo type ones are 25mm), I suppose in theory O rings are only normally used for sealing things and are not really used to being shoved up and down bores at great speed and pressures (but I'm happy to be proved wrong with these sort of applications), so I'd expect a harder shore is needed in this case.

Pete

[james_stan]

OK so I'm up for a bit of experimenting here.. I bought a couple of 22mm id 3mm cs O-rings (shore70) to see how they would fit.. Easy on to the piston and slides nicely
into the bore with some but not a huge amount of resistance - feels pretty good. I have some concerns about the 'side slop' in the 3.5mm groove but the proof of the pudding and all
that. Hope I can the old girl back together tonight for a test out.

Cheers

James

[CapitalBee]

OK so I'm up for a bit of experimenting here.. I bought a couple of 22mm id 3mm cs O-rings (shore70) to see how they would fit.. Easy on to the piston and slides nicely
into the bore with some but not a huge amount of resistance - feels pretty good. I have some concerns about the 'side slop' in the 3.5mm groove but the proof of the pudding and all
that. Hope I can the old girl back together tonight for a test out.

Cheers

James

Sorry for the late reply but I used 22 x 3cs rings also

[T 20]

OK so I'm up for a bit of experimenting here.. I bought a couple of 22mm id 3mm cs O-rings (shore70)

Cheers

James

70 shore is the hardness I always use and seems to be the industry standard.



All the best Mick

[james_stan]

Thanks all - I'm still nursing the bruise in the palm of my hand from fitting the spring (twice - since I left out the guide first time) and now she fires. Power seems lower than I expected but that may well be to do (in part) with the white breech seal which I fear I have fitted upside down..