Scraper ring on Airsporters - what does it do?

[evert]

Working on tne "new to me" Airsporter wreck that somehow wound up home with me,
I am puzzled by the metal scraper ring in front of the O-ring on the piston head.
What was the idea?? Did they think it sealed better?

[TonyL]

I'm no Airsporter expert, but I haven't heard of a scraper ring being present before? Is it, perhaps, a home-brewed addition?

[Neil54]

I believe it adds support to the Oring.

[Shed tuner]

never seen one in an airsporter or merc...

[Dornfelderliebe]

I've found three now on both guns. They were a short-lived alteration which I believe did not work.
By the time I bought my Mk6 Airsporter in 1977 BSA had changed to a Nylon head without the ring. I'm sure Gunshop would know more.

[crowbar]

The Mk4 has the scraper ring and it is rubbish ! but also the aftermarket Ali one is rubbish and your best option is long stroke by shortening the spigot, leaving off the buffer washer and having the O ring undercut 1.5 mm set back from the face , not 10mm as is and it will shooter better .

[evert]

I'm no Airsporter expert, but I haven't heard of a scraper ring being present before? Is it, perhaps, a home-brewed addition?

No this does not look home made. The gun has lived a rough and abusive life, but does not seem to have been opened.

I believe it adds support to the Oring.

How? It is quite far away from the O-ring?

never seen one in an airsporter or merc...

Probably short lived as other posts say, I belive this is an early mk6

I've found three now on both guns. They were a short-lived alteration which I believe did not work.
By the time I bought my Mk6 Airsporter in 1977 BSA had changed to a Nylon head without the ring. I'm sure Gunshop would know more.

Hopefully he'll chime in. This is a nylon head with steel "scraper" in front of the usual rubber O-ring.

The Mk4 has the scraper ring and it is rubbish ! but also the aftermarket Ali one is rubbish and your best option is long stroke by shortening the spigot, leaving off the buffer washer and having the O ring undercut 1.5 mm set back from the face , not 10mm as is and it will shooter better .

Yeah, the gun is running an aluminium after market head at the moment, and it is not great.
I cant really remember if my other later mk6 Airsporter has the steel ring but it has a nylon head and performs surprisingly well. (but my expections for an Airsporter is really low).

The stroker may be a solution in the future, but for now I'm not too keen on making a new piston head.
I did something like that on my Franken-Mercury that worked out quite well in the end, just maximizing the stroke and compression without cutting down the spigot.

[Shed tuner]

The Mk4 has the scraper ring and it is rubbish ! but also the aftermarket Ali one is rubbish...

Thanks for the info.. always more to learn

[TonyL]

[QUOTE=Dornfelderliebe;8368310]I've found three now on both guns. They were a short-lived alteration which I believe did not work.

The Mk4 has the scraper ring and it is rubbish ! but also the aftermarket Ali one is rubbish and your best option is long stroke by shortening the spigot, leaving off the buffer washer and having the O ring undercut 1.5 mm set back from the face , not 10mm as is and it will shooter better .

Thanks for the info.. always more to learn

Thanks for the info, chaps. Yep, every day's a schoolday.

[flatrajectory]

I have serviced millions of Airsporters ... no really... the metal ring you refer to was BSA`s ide of a compression ring. Perhaps they thought adding it would make it like a FWB 300s..!!!!
It reduces available compreesion by shortstoking the piston and adds considerable friction to boot.! A total waste of effort BSA .
Bin it and fit an earlier or later standard O ring head.

Pete.

[TonyL]

Excellent information, Pete. Poor show, BSA.........But, at least it's an easy fix.

[T 20]

I've only ever come across one on a MK4 Airsporter and it went straight in the bin, as I do with all BSA Nylon piston heads.

From memory the O ring groove is over the cross pin so it can't escape, and the steel ring seemed to be there to centralise the piston head in the cylinder bore.

The type of Nylon the BSA piston heads were made from takes in oil and swells over time sapping power, so I always fit an aluminium piston head to avoid this problem.



All the best Mick

[Dornfelderliebe]

I've kept one for posterity and I will try to remember to bring to the bash if any one is interested in it for curiosity value.
Alternatively it will be on the sales table for £20 proceeds to a good cause.

What I did not like was to see how shiny the outer surface was it must have been causing similar wear to the cylinder.

[junglie]

The Mk4 has the scraper ring and it is rubbish ! but also the aftermarket Ali one is rubbish and your best option is long stroke by shortening the spigot, leaving off the buffer washer and having the O ring undercut 1.5 mm set back from the face , not 10mm as is and it will shooter better .

Yep done this with good results on the 635 magnum merc I had.

[Shed tuner]

A diana 28mm seal mounted to a dovetail arbour threaded onto the (shortened) spigot is the optimal efficiency tune for these... lengthens stroke by around 5 or 6mm, and the parachute seal give a much better seal and a soft landing. it literally transforms the firing cycle of the gun, and you gain 2-3 FP