The $100 challenge.....

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Posted: 12 Sep 2023 at 6:51pm

The original piston seal sits on top of that spacer cone at end. The shape of that cone would take a bit of impact out,in my view.
Lets the full flat face upto chamber wall.

KiwiTR6

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Posted: 12 Sep 2023 at 10:45am

Thinking about it a bit more, I might keep the teflon seal but remove the rubber bump stop, I can always make another if it gets munted.

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Posted: 12 Sep 2023 at 10:42am

I use moly on the piston - just a little behind the piston seal and then again on the skirt of the piston. No more than a pea's worth in total.

I would also use moly grease anywhere metal on metal contact - e.g. where spring slides against the main guide and top hat and inside piston where spring and piston contact. If your guides are polymer then skip to the next step using general automotive / marine grease.

I use marine grease on the spring itself. It's viscosity will dull the spring twang. No more than two peas worth over the entire spring.

There is debate on how much grease to use - Tinbum for example recommends running the spring almost dry. I find the marine grease improves the shot cycle. Maccari sells 'heavy tar' for the same purpose. In the UK you used to be able to by 'tune in a can' which was again the same principle - heavy grease on the spring.

Google and Youtube provide lots of opinions on the grease topic!

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Posted: 12 Sep 2023 at 10:34am

Thanks Kruza and Paul for your comments. Definitely the top hat I fitted has to go, I'll replace it with a very slender metal hat just to keep the spring aligned and possibly countersink the end spring stop a little to compensate as you suggest. The spring definitely wasn't coil bound as I could easily compress it beyond the cocking point, but it was obviously putting more load on the cocking shoe. That wasn't out of place but I had reshaped (squared up) the end of the slot in the cylinder which it doesn't seen to have liked. I could be wrong, but it may have also been pushing up against the spring even?

The damage you can see to the new top hat is from me trying to prise it out. It was a tight fit because the cylinder is swaged in - I should have made it slightly smaller. The marks you can see on the original plastic guide is just debris, I haven't touched that.

I'll stick with the original spring for the time being (thanks for the offer Kruza, I may yet follow you up on that) and go back a few steps to the original piston seal and lube up everything with moly grease. What parts should I apply this to and how much on each do you suggest?

Edited by KiwiTR6 - 12 Sep 2023 at 10:35am

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kruzaroad

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Posted: 12 Sep 2023 at 8:01am

Did you cut back the rear top hat reciever? Those look like hacksaw marks. If so and it was before you reinstalled it that is most likely your issue.
Compared to some springs I've seen deemed OK on Web that spring don't look to bad.

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Posted: 12 Sep 2023 at 7:44am

Ouch! Just looking and taking a stab in dark I'd say, the spacer at back of piston has lifted the rear enough that the cocking bar has been able to slip under.
The top hat at other end will have been equivalent to adding a washer as a spacer for more power. You porbly noticed it has one at the original top hat end.
I'm not sure what you've done to the piston head but if that black bit on the front is out further than the original piston seal it's going to be thumping the end with an almighty whack, it also is going to block the port hole and stop air flow before the piston seal/face has got to max end of stroke.
Most of the pressure is created in last 2 inches of travel of piston, when the air is under max pressure, compressed, and forcing through port.
Good news is all repairable.
The spring not sure about, but can be replaced.
Why is the seat for rear top hat so munted?
If you have the tools to remake that whole black trigger/top hat bit in steel, you'll find you will get a tighter fit ( I beat a piece of aluminium can with hammer till thin enough to shim around it), gain mass to the rear, and can tighten tollerances. You could also countersink the hole the top hat sits in to allow washers to fit in which would allow you to add or remove washers to adjust spring tension.
If you need a new spring I can run my down to the spring shop here and get one priced ( only say this as its going to be easier if he can see the spring first before pricing.)
But all said and done, right track, just a few minor adjustments.

Edited by kruzaroad - 12 Sep 2023 at 7:52am

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Posted: 11 Sep 2023 at 10:13pm

Gee, it's hard to know what happened there.

I see you added a small top hat in the piston. Is it possible this has caused spring to become almost bound or the extra pressure pushing the cocking shoe out of the groove and to scrape inside of action? I'm just guessing of course.

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Posted: 11 Sep 2023 at 9:45pm

Well, I'm writing this all again for a second time as for some reason I lost the whole lot while I was mucking around downloading some photos from my phone. It doesn't get any better!

So I spent the day finishing off various parts so that I could get the gun reassembled. I used silicon spray in the cylinder, silicon grease on the piston shaft and moly grease again on the trigger contacts. The difficulty I had trying to install the pivot bolt after this round of 'improvements' should have been a hint of what was to come. This was in addition to a couple of aborted assemblies when I left bits out. I also fitted a rubber spacer made from some heater hose under the cylinder where the hold down bolt connects.

But there was lots of excitement and much anticipation as I mounted the Tasco scope and rings (I'd drilled a hole in the cylinder for the locking bolt) confident that it was all going to come together nicely and I'd be shooting some very creditable groups to impress! I should note at this point that I do all of my indoor shooting standing with a tripod as I'm shooting over my tool chest and my very precious classic car.

Fist cock of the gun was an omen of things to come. It was dreadful with horrendous metal to metal grinding, much worse than any I'd noticed before. I put an un-sighted shot into the target holder and cocked the gun again, much the same. Nothing for it then, I pushed on and after a few shots it started to feel a bit better although I was a bit concerned about how much damage I might be doing to the internals (it's only $100 remember!). Nice crisp firing but with more recoil than I had noticed before. I then did some sighting shots, the group was very similar to my Stage1 shots so I didn't bother sighting it in and moved back to the 10m mark. The next batch of 20+ shots were scattered all over the target. I figured the recoil had killed the Tasco, so I mounted the red dot in the same position on the cylinder grooves but no improvement. OK, so it's the gun then. I moved the red dot forward to the barrel with my original improvised mount and I was back to where I had been at Stage1 i.e. no improvement!

Enough of that then, it all came apart to assess the extent of the damage. The key was the now kinked spring. I assume the top hat and washer I had added has caused this plus the gouging of the piston slot, cocking lever end and the premature wear to the thrust side of the new PTFE piston ring. The rubber stop on the piston seal is also ready to fail. On the positive side, the trigger is still great, the teflon piston and cylinder are both unscathed and the breech now closes with a very satisfying metal to metal 'snick'.

My next move is to try and straighten the spring (any suggestions an this and the next issue will be gratefully received by this newbie) and sort out how to address the cocking lever to piston damage. I was planning to case harden both surfaces but I'm not sure this is the answer. It's an ugly setup, but I guess that's how most are done.

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Posted: 11 Sep 2023 at 9:19am

That's coming out great!
Wouldn't even recognise them compared to as it came.
Its going to be great to see the end results. There should be some very tidy rifles come out this.
Great to watch

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