And if you decide to keep it an O ring head then use a Meteor O ring, instead of the Airsporter one.
Far too many rifles to list now, all mainly British but the odd pesky foreigner has snuck in
The tap on the mk4 is tapered the same as mk1,2,3 but not self indexing and mk5 and on have the parallel two piece tap.
I warm the tap body and coat it in candle wax and then work it in to form a seal.
I was WRONG the tap ts PARALLEL with a outside diameter of half an inch.
Last edited by crowbar; 16-11-2022 at 01:25 AM. Reason: waffle
Steve I had two taps machined .177 and .22 with a groove at either end then tried two sizes of o rings. one did not fit the other fitted but I thought I would try a goldilocks size. After fitting the seals on my 177 the other three went AWOL, but my .177 the bane of my life ended up worse and I have clearly done something else wrong. The .22 responded to treatment well and just tested now at 586,575,586 fps with super domes = 10.8 ish fpe.
In spite of the o rings if I cock it open the tap and release the cocking lever air still comes hissing out of the top of the loading port. WIP.
When I find or buy more of the o rings I shall do an update.
I've been wondering about that and read of people electroplating the tap I'm unsure by how much and of which metal given that it might have to be sized to fit. You are right I may have cured leakage from the ends but it still escapes from the top.
Last edited by Dornfelderliebe; 16-11-2022 at 02:51 PM.
My order from Chambers arrived today. Their supadoopa tuning kit, https://twchambers.co.uk/airgun-spar...4-to-mk7-and-s, an alloy piston head, and a spare piston O ring (just in case).
The buffer washer fitted in mine was white plastic. Hard as a rock, with zero buffering ability whatsoever. It was not even a tight fit between the head and piston. I was surprised just how much I had to compress the new one to get the pin holes lined up. But I did manage it, using a small sash cramp, two half inch drive sockets, and two repair washers. Needs must.
The new piston O rings were too big, IMO. A very , very, tight fit in the cylinder. I fitted a slightly smaller one,(probably for a Meteor), that seems OK. The piston will not drop under its own weight, but needs a fairly light push. The loading tap seems to hold air OK - for now.
The spring that came with the kit is sized as per Cobham, and is 0.5" longer than the one that was fitted. It has a Delrin guide, and a steel Top Hat with a Delrin washer. Maybe the steel TH is to add a wee bit of weight when fitting the alloy piston head? I will see how it performs, and maybe make a delrin TH to see if there is any noticeable difference.
I may also try a piston liner. The spring is quite a good fit in the piston, but I have some 0.2mm PTFE sheet on the boat from China. A liner from 0.5mm PTFE was too tight.
I am keen to get this back up and running again. Then I can continue throwing more money at it.
Steve.
I have just pulled the tap out my MK4 and you are quite right I even put the micrometer across it and it measures up at
.498" and I'm sat kooking at it thinking "wot a nob" it's old age and that MK2 tap I was playing with a while back.
Thankyou for pointing out my mistake and I will remember (Ithink) it's PARALLEL!!
Cheers Crowbar