BT 65 valve and poppet questions?

[customcutter]

I just realized it's been 15+ years since I've made any spreadsheets.  Who knew that corporate stuff was useful.

[customcutter]

I've re-assemble the rifle.  It is a lot smoother, but not much lower on the cocking force needed.  I'm going to tune it to around 900fps and see how the shot string goes.  At least I'll have some starting data for comparisons.

I've had the gun torn apart and scattered all over my wife's kitchen counter for the last 2 days, so I better give it a rest while I'm still ahead. In a couple of days I'll tear it down again and start on the new peek seat.  Need to try and source some different springs as well. 

More questions have come up concerning a seat made of peek.  The original is white delrin I'm guessing, and the spare one that I found in the bag of parts is flat on both sides.  The seat that I extracted is shaped to the cone on the stem, presumably by pressure.  My understanding is that peek is much harder.  So I should machine the peek seek to match the cone on the stem?  Should I also try to lap it in with something like valve grinding compound to insure a good seat?

Thanks again for all the help everyone is offering.

[sb327]

The more  ‘cone’ in the seat, the larger the sealing diameter, the higher the cracking force needed.

Also, when lapping, the softer material holds the compound while the compound cuts the harder material. Your poppet is good so I suggest NOT lapping with compound.

What can be done, however, is cut your seat square and BURNISH it with the poppet. If done gently, this will make a minimum sealing diameter and true up the seat with a very mild cone.

Dave

[customcutter]

Thanks again Dave.  I received some .5" natural peek last week.  When I get ready I'll follow your advice.

[Thane]

My first attempts at Hatsan tapered seats were difficult. The most successful PEEK seats I made were 90° square cut, no bur, no additional operation. Because of PEEK's high compression strength tapered seats deform less are prone to leak with any surface deviance, while the 90° corner crushes a bit making a good seal. Just a hard first fill seats the valve.

I turn the outer diameter, then drill the smallest desired center bore, face, groove for oring, and then parting tool no other operations. I usually make a few, increasing the bore diameter for a tuning set, while the peek is set up, reduces waste material.

Explore using a brass slug in your hammer to increase opening force without increasing spring force.

You should be making full strings to see what you are trading with different set ups.

[customcutter]

Thanks, that pretty much sums up my plan.  Other than the hammer already weighs 90+grams.  I want to maintain FPE, but most importantly reduce the cocking force needed.  I've even considered trying to fab some type of cocking lever like on the AT44. 

I ordered a piece of 1/2"x12 natural and it is labeled .500, which is what I got when I measured the spare delrin seat with a caliper.  I'll dig the mic out when I start cutting.  Thanks for the idea of making a few hadn't thought of that so I'll probably do 2-3 to save set up time.

[customcutter]

I aired up the BT65 earlier to 100 bar, shot it 3 times to make sure the valve was seated.  Then I filled it to 200 bar and let it sit for a few hours.  As expected it dropped to almost 190 bar.  IDK if it was heat from filling or leakage, so I topped it back at 200 bar and let it sit another hour.  The hammer spring was backed out flush with the back of the gun and I haven't cut a channel in the stock to back it out more, so I went with the setting I had.

It was still holding 200 bar so I loaded some 24.7gr Vortex Strike .25 cal.  The magazine holds 9, I thought it was 10 so I had 1 mis-fire.  I fired 3 magazines and it was almost dusk so I had several ERR's.  Here is the shot string.
938/961/ERR/956/968/ERR/962/964/980/EMPTY MISFIRE/  165BAR
975/963/975/ERR/979/973/ERR/972/969  137BAR
963/ERR/ERR/921/925/ERR/ERR/901/ERR

As it sits I think I'm looking at 20 good shots.  Just over 2 mags. I'll try to get the new peek seat made and get some more info.  Still need to find some springs, forgot about that.  I know I have a couple of spares for my Evanix Rainstorm when I ordered it.

[mann]

With using peek it's harder so you don't need as big of a poppet head which helps with the cracking force may have to sand the peek using the poppet to help get the shape and to get it to seal I would color the seat made of peek and start with like 800 grit fold the paper in half and push stem threw it then push the stem into the valve and on the poppet seat sand until the sharpie marker is gone I'd do it a couple times the I'd go to 1500 grit and do the same color the seat with the sharpie and spin the poppet around on it till all the marker is gone I would also polish the poppet to a mirror finish find out what the hole size in the seat is and measure poppet head peek is alot strong and I'd take poppet head and make it about .060 of a inch larger than the seat hole is should lighten up cracking force quite a bit to either need to lighten the spring up or the hammer then or some of each

[mann]

Never had any luck burnishing in a peek poppet I've had to lap it in with some good metal polish to  I had good luck with the sanding I described and also lapping in with metal polish

[customcutter]

Never had any luck burnishing in a peek poppet I've had to lap it in with some good metal polish to  I had good luck with the sanding I described and also lapping in with metal polish

Thanks for the suggestions.  I'll try burnishing first and if it doesn't work, I'll move onto other options.

[customcutter]

I managed to get 2 peek seats made today.  1 has a .250" opening same as the old seat, and the second is .225".  I had to use 1.5mm o-rings, as I don't have any 1mm like the originals.  Burnished both with the stem, by chucking the stem in the tailstock.  I left the stem at the original diameter for now.

Just inserted the .250" seat into the cylinder and hit it hard with a few blast of air.  Finally got it to partially seal and aired it to 100 bar, which it's holding for now.  Going to let it cool off, then take it to 200 bar before calling it a night.  I'll check in the AM to see if it's leaked down.

Time to dig out 1 of the Evanix RS II hammer springs and see if it will fit.

[customcutter]

I found the Evanix springs.  It measured:

2.8" long, .48" wide, .051" thick  with 11 coils and I cut it 10 coils.  The Hatsan spring was:
2.6" long, .492 wide, .056" thick with 12 coils.  So it should have been stronger.

Re-assembled everything and it feels a little better.  I'll try a shot string tomorrow and see what happens.  Cylinder holding 200bar for now.

[customcutter]

I shot another 3 mags this morning with the mods.  Tried loading the Caldwell Chronograph app onto my tablet.  Can't get it to work for some reason, I know most people use cell phones?  This was the original readings:
938/961/ERR/956/968/ERR/962/964/980/EMPTY MISFIRE/  165BAR
975/963/975/ERR/979/973/ERR/972/969  137BAR
963/ERR/ERR/921/925/ERR/ERR/901/ERR  105BAR

This is this morning readings, with the peek poppet, and slightly weaker modified spring:
988/992/1003/1004/1013/980/empty/1003/993/990  160bar
987/986/982/973/967/958/956/947/936  130 bar
937/935/925/918/905/895/892/881/878  105  bar

Not sure what to make of the readings.  It appears that the valve is easier to knock off 938vs988 with a weaker spring.  I need to find a weaker spring for sure.  Right now both springs are backed off completely AFAIK.  Should I try cutting another coil or 2 off?  I read another thread last night that said cutting coils actually made springs stronger!  (Doesn't make sense to my 2 brain cells.)   I looked through Amazon last night looking for compression spring kits.  Didn"t find anything suitable so far.  As soon as I get the cocking force reduced more I will start with the other mods in the video.

[PikeP]

FWIW your original spring was around 14.5~ lbs and your second spring from the evanix is around 11.2 lbs/in

Both have some heft, you could try to get down to 8 or 9 lbs, I think that rating can be found at mcmaster and its so common maybe a member here has one around that.

[sb327]

Clipping coils increases spring RATE. When you say an 11 lb. spring, you are really meaning 11 lb/inch of travel.

If you compress that spring 1”, it will push back with 11# of force. Clip it down to 1 coil left and it will push back with same 11# force with just a minimal amount of travel. But it obviously doesn’t have the equivalent stored energy. Which is what we want.

It is ok (and I prefer) some free flight to my hammers so it is ok to go pretty short.

Dave

[customcutter]

FWIW your original spring was around 14.5~ lbs and your second spring from the evanix is around 11.2 lbs/in

Both have some heft, you could try to get down to 8 or 9 lbs, I think that rating can be found at mcmaster and its so common maybe a member here has one around that.

Thanks Matt, I know there is a formula for calculating.  I saw one on a site I visited a couple of nights ago.

[customcutter]

Clipping coils increases spring RATE. When you say an 11 lb. spring, you are really meaning 11 lb/inch of travel.

If you compress that spring 1”, it will push back with 11# of force. Clip it down to 1 coil left and it will push back with same 11# force with just a minimal amount of travel. But it obviously doesn’t have the equivalent stored energy. Which is what we want.

It is ok (and I prefer) some free flight to my hammers so it is ok to go pretty short.

Dave

Thanks Dave, it's a spare spring, so no harm in cutting it shorter.  The spring rides inside a hollow section of the hammer and another hollow section at the rear which also houses the trigger, and hammer spring adjustment bolt.  I'll take another couple of coils off and see where I'm at.

[customcutter]

I took the gun apart for what seem like the 100th time.   I got the spring to where I had about 1/8" of free travel.  First shot was around 500FPS, so I adjusted the HS to get 950, and aired the cylinder to 200bar.  Here are the 2 earlier strings:

938/961/ERR/956/968/ERR/962/964/980/EMPTY MISFIRE/  165BAR
975/963/975/ERR/979/973/ERR/972/969  137BAR
963/ERR/ERR/921/925/ERR/ERR/901/ERR  105BAR

This is this morning readings, with the peek poppet, and slightly weaker modified spring:
988/992/1003/1004/1013/980/empty/1003/993/990  160bar
987/986/982/973/967/958/956/947/936  130 bar
937/935/925/918/905/895/892/881/878  105  bar

Trimmed ERS spring trimmed and adjusted to 950fps:
948/965/957/962/967/965/961/969/937  165bar
978/960/966/985/981/960/959/972/988  145bar
961/964/962/963/953/942/935/954/929  115bar

Cocking is definitely easier and probably would be better at 900fps or with a 10#spring.  Time to start working on the valve body.  Any thoughts on lightening the hammer from present 93 grams?



 

[mann]

You could try it so the hammer is in free flight for the last .030 thousandths of a inch or a tad more with the heavier spring just cutting it shorter a little at a time that way it isn't preloading the hammer when uncocked and the 30 thousandths gap or tad more of free flight on the hammer will help with hammer bounce saving air also this is the basic idea of a ssg but you can load spring pressure on the ssg and still have 30 thousandths free flight on the hammer if you can make a peek poppet you can make a ssg  pretty easy to do

[customcutter]

I vaguely remember the SSG from when I was active a few years back.  Seemed like a Marauder Mod at the time.  Isn't it basically a double spring?  If so that would be increasing the cocking force again.  Or maybe I'm confused about it, I'll have to look it up. 

Thanks, Ken