BT 65 valve and poppet questions?

[customcutter]

I'm going to finally start working on the BT65, trying to reduce the cocking force.  I'm going to polish the inside of the hammer tube.  Right now I can see and feel the machining marks on the inside.  Then burnish it with some Tungsten Disulfide.

I've taken the valve apart and can't get the white delrin seat out of the valve.  I've tried using a dental pick pushing from the hammer side.  I don't want to damage it. Someone suggested replacing it with a seat made of PEEK.  The existing stem has a taper that fits the seat.  Should I make the PEEK seat with the same taper, or make a new stem with a flat surface and smaller surface area?  Will this reduce the force needed to break open the valve?  What about using a lighter spring to reseat the valve once it breaks open? 

[customcutter]

Progress so far.  I made a mandrel from 1/2" hardwood dowel.  Then used 1/3 sheet of 150 grit to remove the rough machining.  By the time I was through it was probably worn down to close to 400 grit.  Then I cut a piece of 400 grit and repeated the process.  Here are the results of polishing the hammer tube.

[customcutter]

After polishing with the 150 grit I could still feel some rough spots, so I looked at the edges on the hammer itself.  I noticed a couple of high spots on the top next to the brass tube so I took them down with a file.  It was slightly better, but not good enough.  So I looked at the edges again on  the hammer and noticed some sharp edges on the corners of the larger outer rings.  I decided to buff them slightly and "break" the edges with the scothbrite wheel on my buffer.  Much better, the hammer slides through now by only slightly tilting the tube rather than the almost 45* angle before.  Next, I'll apply and burnish some Tungsten Disulfide on all contact edges.

[customcutter]

Here's a pic of the existing poppet for reference as far as the angle.  Still haven't been able to remove the white delrin seat in the valve body.  Looking from the hammer side of the valve there appears to only be about .010" visible above the brass valve body.  I'm assuming that it's a press fit into the body. 

For those who have made PEEK seats, would you stay with an angled shaft/seat arrangement, or make one with a 90* sealing seat?

[mann]

I haven't messed with peek seats but have done peek poppets and are easier to get to seal with a angle vs being 90 degrees is polish the hammer to mirror finish and also do the same to the poppet and stem

[mann]

As far as changing the valve return spring you can but it will increase your dwell time also so I'd try it with the original spring  also if you can round and polish air ways in the valve transfer port side round any 90 degree corners and mirror polish the passage ways  the valve should lift off the peak easier since it is a harder material and rounding 90 degree passage ways will help air flow quite a bit

[customcutter]

As far as changing the valve return spring you can but it will increase your dwell time also so I'd try it with the original spring  also if you can round and polish air ways in the valve transfer port side round any 90 degree corners and mirror polish the passage ways  the valve should lift off the peak easier since it is a harder material and rounding 90 degree passage ways will help air flow quite a bit

Mark, thanks for the replies.  I'll stick with the angled stem/seat for now.  The main focus at this point is reducing the cocking force.  Once I do that I will seal 5 of the 6 ports on the valve body and work on transfer ports, etc.  I need to check my scraps, check the local scrap yard.  I might be better off making a new valve body, stem, and poppet.  Before I get carried away and damage this one.  

[sb327]

I’m not familiar with the bt (although I’m learning hear).

It appears the stem of poppet is rather large compared to the poppet head. The stem is where the most significant closing force generally develops from. The spring is quite negligible when the stem is oversized. Also, Mann mentioned an increase in dwell time due to smaller spring. I may be wrong, but when people want a lighter cocking force/same fpe, anything that usually increases dwell GENERALLY helps. When the hammer strikes the stem, it has X amount of energy. Part of the energy is used to crack the valve and the rest is used to create dwell time.

You can increase dwell with less hammer strike by simply decreasing stem size. What are your stem dimensions?

What is the purpose of the black disk/bolt on the stem?

Enjoying your upgrade here.

Dave

[mann]

Stem does seem awful large I agree with you  and don't know this valve either

[mann]

Depending on measurements on the the stem I would only reduce area directly behind the head to where it steps up  I would  take it down to just under .125 or 1/8 inch   have had success down farther at like .100 to ..080 but starting to get thinner than I'd like to be leaving the step in there may have to 45 degree it but after that I'd leave that area alone being it probably steps up to fit the valve properly and seal the rear of it with small oring in there

[sb327]

It is the sealing area that causes the closing force. Cutting it down in just the throat area only improves flow.

A bushing would need to be made to accommodate a smaller stem unless op proceeds with making a new valve body. At which point, it could be considered in the design.

Dave

[customcutter]

I’m not familiar with the bt (although I’m learning hear).

It appears the stem of poppet is rather large compared to the poppet head. The stem is where the most significant closing force generally develops from. The spring is quite negligible when the stem is oversized. Also, Mann mentioned an increase in dwell time due to smaller spring. I may be wrong, but when people want a lighter cocking force/same fpe, anything that usually increases dwell GENERALLY helps. When the hammer strikes the stem, it has X amount of energy. Part of the energy is used to crack the valve and the rest is used to create dwell time.

You can increase dwell with less hammer strike by simply decreasing stem size. What are your stem dimensions?

What is the purpose of the black disk/bolt on the stem?

Enjoying your upgrade here.

Dave

If you look at the hammer face it is slotted from top to bottom on the edge that strikes the stem. 
The black disk threads onto the end of the stem and is held in place by the nut.  So the hammer actually strikes the black disk, rather than the stem.

Stem measurements starting at the black disc are 2.1 long overall, .195" thick behind the black disk, then steps down to .157", .368" width at the poppet, .216" on the end that retains the spring.

I'm not sure why there is an o-ring behind the poppet in atmospheric pressure? 

[customcutter]

Depending on measurements on the the stem I would only reduce area directly behind the head to where it steps up  I would  take it down to just under .125 or 1/8 inch   have had success down farther at like .100 to ..080 but starting to get thinner than I'd like to be leaving the step in there may have to 45 degree it but after that I'd leave that area alone being it probably steps up to fit the valve properly and seal the rear of it with small oring in there

Yes, the thicker section right behind the black disk is the tolerance for guiding the stem in the valve.  I'm not sure why the o-ring is there though as this is behind the pressure/seal on the poppet and in atmospheric pressure?

[customcutter]

Here is a different picture with the parts laid out.  Trying to show the slot in the huge (93 gram) hammer.  I couldn't get a pic of the inside of the valve showing the delrin seat.

[sb327]

The point that is .195” (with the oring) is the point (diameter) that BECOMES THE SIGNIFICANT CLOSING FORCE once the valve cracks open. The pressure inside the throat makes the stem act like a piston, forcing the hammer back and allowing the valve to close. Once pressure drops, it’s just a guide for the stem. The oring is to keep air from leaking into hammer area during the shot cycle. Most don’t use one due to drag ( I don’t).

Another hammer force robbing area is that plastic disk. It doesn’t transfer energy very efficiently.

Dave

[mann]

 Better flow will increase the power it should also lift off the peek seat easier to being peek doesn't flex like derlin does  increase of power and dwell can hurt efficiency by lightening the stem and increasing flow it should help opening but and if you change the spring to lighten it up more it will or could be worse on efficiency you want a balance and is why I said to try it with the original spring first    as for the oring some valve designs have it to seal the stem for blow by when the valve is open usually blow by is so minimal that isn't needed

[sb327]

FYI

A stem .195” od develops a closing force of roughly 60# at 2000psi

A stem .125” od develops a closing force of roughly 25# at 2000psi

Dave

[mann]

I just didn't want him to have to sleeve the valve the valve or make a new one     otherwise I agree with you and understand what you are saying

[customcutter]

The point that is .195” (with the oring) is the point (diameter) that BECOMES THE SIGNIFICANT CLOSING FORCE once the valve cracks open. The pressure inside the throat makes the stem act like a piston, forcing the hammer back and allowing the valve to close. Once pressure drops, it’s just a guide for the stem. The oring is to keep air from leaking into hammer area during the shot cycle. Most don’t use one due to drag ( I don’t).

Another hammer force robbing area is that plastic disk. It doesn’t transfer energy very efficiently.

Dave

Thanks for the explanation.  I thought the main closing force was the HP air escaping past the flat back side of the poppet area.  I can see where the air passing the thinner section also would push against the stem forcing it to close.  I guess the 45* angle is more efficient at getting air to the transfer port area, instead of a 90* step.  Also if were a 90* angle it would be a stress riser on the stem.

[sb327]

I just didn't want him to have to sleeve the valve the valve or make a new one     otherwise I agree with you and understand what you are saying

Of course. I’m certainly not trying to say this is a have to change thing. I was just wanting to make sure all of the areas that rob power from the hammer strike were known. Efficiency is a different item as well but you shouldn’t have to deal with a hard to cock hammer for good efficiency.

The 45 degree taper at the seat may help a little with air flow but it’s main advantage is dependable sealing of the poppet. This along with soft poppet material make for a more dependable gun….at the expense of harder cocking force. The manufacturers don’t care as much about easy to cock as they do about dependability (meaning less returns).

Dave