MRod Valve Mods

[rsterne]

Quite a long time ago, even though I didn't own an MRod, I bought a Gen 1 valve in .25 cal to see what could be done to improve what appeared to be dismal breathing.... I did a lot of measuring, and discovered that the largest you could go on the exhaust port was about 3/16", or you ran the risk of breaking through into the back of the valve chamber, and ruining the valve.... I published that on the GTA just about the same time a couple of guys did just that, and toasted their valve, but hopefully the word got out, and it prevented more from ending up in the garbage.... Thanks to Travis at W.A.R. I recently was given some Gen 2 valves (along with a box of other pieces), so I set out on a quest to make the MRod valves breathe at least as well as my Disco valves.... Here is a photo of how much the Disco valve can be improved....



The stock exhaust port is 0.141" at 90*, and there is enough material in the valve body to enlarge the port to 0.219" at a 20* angle towards the throat.... The transfer port seat has been bored out to 5/16" to allow for the larger TP required.... The new port is 140% larger in area (2.4 times the flow) compared to stock.... The drills sitting in the ports below are the stock 0.141", and my modded 0.219"....



In addition, the throat can be drilled out to 0.266", and by sleeving the stem hole down from 5/32" to 1/8" with brass hobby tubing, you can use the much better and smaller MRod poppet.... This eliminates the need to bore out the inside of the Disco valve for clearance around the Disco poppet, or for grinding down the stem, and the MRod poppet allows you to use up to 3000 psi, provided you don't go any larger than 0.266" on the throat ID, and the valve is secured with three 10-32 screws, of course.... If you go larger than that, the Delrin will extrude into the throat at 3000 psi.... The stock throat on a Disco valve is 0.203".... Enlarging the throat of the valve does, however, mean that it takes more hammer strike to open it, at the same pressure.... At 3000 psi, that becomes a serious problem....

Enough about the Disco, this thread is about how to hopefully get an MRod valve to perform equally well.... First, here are photos of a stock Gen 2 valve, and my Stage 1 modded valve.... The TP flat has been spot milled out to 5/16" to allow for a larger transfer port....




I drilled the exhaust port out in steps, and decided that 3/16" was not a problem, so I went slightly larger, using numbered drills, and ended up at 0.196".... I understand some who are braver have gone to 0.200", and I heard that one guy got to 13/64" (0.203"), but the wall between the front of the exhaust port and the back of the valve is so thin, I have a feeling that eventually, at 3000 psi, metal fatigue may crack it, dumping the air and ruining the valve.... If there happens to be a pellet in the barrel at the time, the gun will fire that, so this is not something to be disregarded.... I would therefore recommend that if you do this mod, you stop at 3/16" for safety.... The drill in the Stage 1 valve below is 0.196" diameter, compared to 0.141" stock....



As you can see, this is a sizeable increase over stock, at 3/16" (0.188") it is 78% larger in area than a stock valve (~1.8 times the flow), compared to stock.... In combination with enlarging the exhaust port, you need to enlarge the throat of the valve, or you will gain little.... The stock throat is 13/64", with a 1/8"stem obscuring part of that, so the equivalent diameter hole would be just over 5/32", or 0.160".... If you increase the throat to 15/64" (0.234"), that brings the area up to the equivalent of a 0.198" port, slightly larger than the largest exhaust port you can obtain by drilling straight into the valve.... You would think that would be all you can get, but in fact because the exhaust port is so long, a larger throat will allow the air to get around the corner easier, so going all the way to 17/64 (0.266"), which is the largest that the MRod poppet can handle at 3000 psi, will give a bit more power....

Getting the air out of the valve better doesn't help if the air can't get into it.... That is covered in the next post....

Bob

[rsterne]

The front cap of the MRod valve, like the Disco front cap, is only 1/4" ID.... If you use the stock valve spring, in either valve, you can only drill that out to about 17/64" or the hole becomes too large for the spring to seat against.... My solution on my Stage 1 valve was to mill two slots along the sides of the end cap, a messy and difficult job.... I later found a conical spring that was perfect for the job, from Century Spring, their # TA-2122.... This allows you to drill out the end cap to 13/32" (0.406") which is the ID of the large end of the spring.... You also have to shorten the front cap by removing the shouldered area, as shown in the photo below....



The new spring doesn't have quite as much preload on the poppet as the original, but enough to do the job, although if you have a really strong hammer spring you may have to cock the gun to fill from zero.... The big difference is the amount of flow that can occur between the coils of the spring, and in particular into the valve.... The view below shows the difference....



The valve on the left is stock, and the one on the right shows the huge hole allowed with the conical valve spring.... At this point, there really wasn't any more I could do to increase the port sizes without a major modification to the valve body.... There simply wasn't enough room for a larger exhaust port.... I had heard of guys installing a new valve seat, so that the port could be made larger, but I wanted to get to the same size ports as on the Disco valve, and on a 20* angle to improve the flow.... so I took one of the sample valves that Travis sent me and hacked it up until I found out how to do it.... I will be taking photos of the steps involved, but here is a drawing of the results, showing a stock valve for comparison....



The key to the Stage 2 valve is drilling the valve out to 1/2" and permanently installing a piece of 1/2" aluminum rod about 3/8" long (shown in red) to move the valve seat forward.... This allows room for a 0.219" exhaust port on a 20* angle, just like on the Disco valves.... Since the seat is 0.150" further forward, the poppet moves that far forward as well.... That means that when the hammer hits the back of the valve, the poppet will only open a bit over 0.100", which may not be enough in some applications.... To allow more lift, I machined some material off the back of the valve.... These changes increase the maximum hammer travel by 0.150", which will be useful to overcome the greater closing force because of the larger valve seat.... The blue poppet is shown open 0.100", and you can see how much more room there is around it for flow.... As in the Disco valve, the area is 140% greater than stock, giving 2.4 times the flow.... More to come when I get the time to machine another valve and take photos along the way....

Bob

[screwwork]

Bob,

What do you think about opening up the ID from where you shortened Mrod valve cap ends to the forward breech mounting screws and also between breech mounting screws to the Alum insert.
I know it is a small amount of area that could be opened up from 0.500 to 0.6875 ID would that help any in increasing the total volume CC's of the valve and increase flow?

[supertech77]

great info bob, thanks.

[shorty]

Thanks Bob,

Now I can see how your gonna solve the TP sleeve problem I have.

It Looks like the rapid fire from TP leak is from the valve to pressure tube. A possible secondary valve oring right past the exit port on the valve may be needed and helpful.

Ofcourse that doesn't solve the root cause but I am sure you can square that up for us (me).

[rsterne]

Randy, there is no point, IMO, increasing the volume inside the valve, when by enlarging the inlet the entire 215 cc reservoir becomes, effectively, the valve volume.... If it would aid the flow around the poppet to any useful degree, then I could see it.... However, as I stated above, once the valve is drilled to 1/2", the area between the valve ID and the poppet OD is nearly 3 times the largest throat and port that the poppet can support supplying air to....

As you state, you have to leave the section where the 4-40 breech screws penetrate the valve body at 1/2", you can only bore it larger either side of that.... I see no point in going larger in ID on the front side of the screws at all, you are just creating a ridge for the air to hit.... On the back side, only boring the valve out larger than 1/2" would prove positively (by comparing it to one merely drilled 1/2") if there were any gains.... IMO there won't be, but I have been wrong before.... I can tell you that I have bored Disco valves out larger than their stock 1/2" ID, and with the stock poppet (which is larger than the MRod one) there is a slight difference.... However, when an MRod poppet is installing inside a Disco valve, boring the valve ID larger than 1/2" is a waste of time.... I have seen no gains, so why would the MRod valve be any different?....

The exception may be if you make a PEEK poppet that is larger than the MRod one, so that you can use an even larger valve throat.... For example, if you made the poppet OD a full 3/8", there would only be a 1/16" gap around it, if the valve ID remains at 1/2".... That area is the equivalent of a 0.33" hole.... If you then drilled the throat of the valve to 5/16", and the exhaust ports to 9/32", you might gain some flow around the poppet OD by boring out the valve ID, but only BEHIND the breech screws.... In fact, I'm not sure you would even gain much then, because with the poppet moved forward far enough to allow a 0.281" exhaust port, and then open, say, 0.1", it would be very close to that portion of the valve where the breech screws dictate the ID not exceed 1/2"....

shorty, I plan on using either a 3/8" OD Teflon transfer port (I have no problem with them leaking), or possibly a 3/8" OD brass TP with a shoulder, sealed to the valve with an 8mm x 1 mm Metric O-ring in the valve counterbore....

Bob

[rsterne]

Progress is going to be slow, as I have to grab a few minutes of shop time here and there between manning the front desk of the Motel.... Here is the start of the machining on the valve.... First a photo of the inside of a stock Gen 2 valve....



You can see that the main ID of the valve steps down before you get to the location of the 4-40 breech screws.... The first step was to chuck the valve in the lathe, and drill it out to 1/2" ID all the way back until the tip of the drill broke into the exhaust port....



You can see the exhaust port, and to it's left the threaded hole for the velocity adjusting screw.... DO NOT forget to remove that screw before drilling, when the drill bit touches that steel screw, nasty things could happen.... You can't really see it in that photo, but the bottom of the hole at his point is tapered, the same shape as the drill point.... We need it square, to match the aluminum plug we are going to install, so the next step is to change over to a 1/2" end mill, and continue deeper, until the exhaust port is JUST removed....



For the last little bit, I machine deeper a few thou at a time, and keep checking until the exhaust port is just gone.... You can see a tiny remnant of it remaining in the photo above.... If you look closely, from about 10 o-clock to 12 o-clock, just this side of the square bottom of the hole, you can see where the velocity adjusting screw hole use to be.... That will end up being covered by the aluminum plug when installed....

When I get a chance, I will make and install that plug, and post those steps....

Bob

[Airgun.Sniper]

 Why would one mess with valve = besides maybe for the power increase? What aer the other benefits?

[rsterne]

Yep, you nailed it.... power hungry mad scientist here.... guilty as charged.... Actually, it will also allow more power at lower pressures, and properly tuned can increase the efficiency as well.... Of course not when you run it wide open.... 

Bob

[PakProtector]

Hey Bob, what sort of glue will you fix the insert with? Have been contemplating using just the drill, and machining a point on the plug, and filling some of the remaining port with epoxy( also for fixing the plug ). Small flat instead of a sharp tip so the valve guide can be drilled with a bit more assurance of keeping a single axis.
cheers,
Douglas

[screwwork]

Randy, there is no point, IMO, increasing the volume inside the valve, when by enlarging the inlet the entire 215 cc reservoir becomes, effectively, the valve volume.... If it would aid the flow around the poppet to any useful degree, then I could see it.... However, as I stated above, once the valve is drilled to 1/2", the area between the valve ID and the poppet OD is nearly 3 times the largest throat and port that the poppet can support supplying air to....

As you state, you have to leave the section where the 4-40 breech screws penetrate the valve body at 1/2", you can only bore it larger either side of that.... I see no point in going larger in ID on the front side of the screws at all, you are just creating a ridge for the air to hit.... On the back side, only boring the valve out larger than 1/2" would prove positively (by comparing it to one merely drilled 1/2") if there were any gains.... IMO there won't be, but I have been wrong before.... I can tell you that I have bored Disco valves out larger than their stock 1/2" ID, and with the stock poppet (which is larger than the MRod one) there is a slight difference.... However, when an MRod poppet is installing inside a Disco valve, boring the valve ID larger than 1/2" is a waste of time.... I have seen no gains, so why would the MRod valve be any different?....

The exception may be if you make a PEEK poppet that is larger than the MRod one, so that you can use an even larger valve throat.... For example, if you made the poppet OD a full 3/8", there would only be a 1/16" gap around it, if the valve ID remains at 1/2".... That area is the equivalent of a 0.33" hole.... If you then drilled the throat of the valve to 5/16", and the exhaust ports to 9/32", you might gain some flow around the poppet OD by boring out the valve ID, but only BEHIND the breech screws.... In fact, I'm not sure you would even gain much then, because with the poppet moved forward far enough to allow a 0.281" exhaust port, and then open, say, 0.1", it would be very close to that portion of the valve where the breech screws dictate the ID not exceed 1/2"....

Bob

Bob,

Thanks for replying about opening up the ID of valve past 0.500 ID, I understand now why not to open it up past 0.5 ID bore.
 

[MichaelM]

Looking really good Bob!! I like the use of the conical spring... I am a big fan of them to be honest... they work great for getting that airflow into the valve and what I used for the mods to my b50 build....

when I did the gen 1 Mrod valve I had nothing on hand so I did the bore and milled slot to increase airflow... I also opened it up straight through with a 17/64 bit then bored from the rear with an endmill leaving just enough material to form a seat for the stock spring and then slotted it .... and your right it was a pretty labor intensive bit of work that is easier done with a straight through drill and a conical spring!!  though it looked pretty good when I was finished:)









so much easier to just replace all that work with a conical spring!!!!

[rsterne]

This evening I got some time to make and install the plug.... It is made from a short length of 1/2" diameter aluminum bar, 0.4" long....



It must be a nice sliding fit inside the valve.... not tight, and not loose, with just enough clearance for glue.... You want to make sure that the plug fits completely down into the valve, against the bottom of the milled hole, but will slide out when the valve is turned upside down.... I used Loctite 638 bearing retainer (green), and applied some inside the valve, and some on the back and sides of the plug, and then slide it down into place, spun it around with the tip of a screwdriver to make sure the Loctite covered all the sides and back of the plug, and then pushed it down to make sure it was seated firmly.... I used some paper towel wrapped around the screwdriver to clean the inside of the valve.... A bit of the Loctite collected in the exhaust port and velocity adjuster holes, and the valve stem hole, so I mopped out the excess, and then making sure there was NO Loctite in the threads, I installed the valve spring and end cap, with just enough tension to put slight pressure on the plug.... I used the shank of a 1/8" drill, rotated by hand in the valve stem hole, to make sure there was no Loctite in there, and set the valve aside, base (back end) down, for an hour to dry.... By that time the Loctite was set enough there is no way the plug would move, so I cleaned the remaining film of liquid out of the exhaust port and adjuster hole, and set it aside to dry thoroughly.... At that point, it looks like this....



I used a bottoming tap to carefully remove the semi-hardened Loctite from the threads of the adjuster hole, and the stem of a 9/64" drill to clean out the residue in the exhaust port, and then blew through in both directions (they are still connected, even with the plug in place) with compressed air until both holes were clean and dry.... I determined that a 3/16" long 8-32 setscrew, when installed flush with the shoulder in the adjuster hole, was still about 1/16" clear of side of the plug, then I mixed up some JB Kwik (5 minute JB Epoxy) and put a generous drop in the adjuster hole, and installed the setscrew until it was just below flush with the outside of the valve.... This pressed some of the Epoxy through into the exhaust port, but not enough to even half fill it.... I wiped off the excess Epoxy from around the setscrew, and set the valve aside, with the adjuster hole down, until the Epoxy on the mixing board was hardening but still sticky.... When Epoxy is at that stage, you can move it around, but it won't stick to anything wet, so I dampened the shank end of the 9/64" drill bit, and slowly twisted it into the exhaust port, using it to clean the excess Epoxy from the port.... If you wait too long, you can use the flutes of the drill, and just spin it in the port with your fingers to remove the excess Epoxy from the port.... The idea is to leave the adjuster hole completely full of Epoxy, and the setscrew permanently glued in place, but to have the exhaust port clear and be able to slide the shank of the 9/64" drill in and out easily, as you will be using it for alignment later.... It looks like this at that stage....



Remove the drill, and set the valve aside overnight for the Loctite and Epoxy to harden completely.... Do NOT ever try and remove the setscrew from the adjuster hole, it is acting as a plug, sealed by the Epoxy to prevent a pressure leak from the exhaust port during firing.... More tomorrow, time permitting.... BTW, I see no reason that you could not use a good Epoxy, like JB Weld or JB Kwik, to glue in the aluminum plug and fill the adjuster hole, all I one step.... It would just be more difficult to keep the inside of the valve clean, and you may need slightly more clearance on the plug diameter.... Since the plug is retained by the back of the valve, all you are really doing is sealing it, and holding it in place for the remaining machining operations....

Bob

[jhm757]

Why would one mess with valve = besides maybe for the power increase? What aer the other benefits?

It's all about the power!!!

Jim - jhm757

[rsterne]

Well, I managed to get the rest of the machining on the valve done today.... The following two posts will show the completion of the mods.... After curing overnight, I chucked the valve in the lathe by the front, and using a 1/8" drill, carefully drilled through the plug, using the valve stem hole as a guide.... You want to take it slow and clean the swarf often, because you don't want the chips to gall the inside of the valve stem hole and enlarge it.... Once the hole for the stem was drilled through to the inside of the valve, I turned the valve around and grabbed it in the chuck by the back end, and drilled the throat out with a 3/16" drill, and then a 1/4" drill, stopping 2" from the front face of the valve with the drill point.... I then changed to a 17/64" drill (0.266") and set the corner of the flute level with the front face of the valve, and drilled in to a depth of 2", measured from the front of the valve to the full diameter of the hole.... I then removed the valve from the chuck, blew out the chips, and prepared to mill the angled exhaust port....

The first step was to install my Milling Attachment on my lathe.... It replaces the compound feed, and is adjustable for any angle in two planes.... This is an ideal setup for drilling a hole on an angle.... I started out with it set to hold the valve at 90* to the lathe centerline.... I first used an edge finder and calipers to set the height of the valve with the centerline at the height of the chuck.... I then chucked a 9/64" drill bit backwards, so that I could use the shank inside the original exhaust port to line the valve up in both directions, and in rotation, so that the new port and transfer port recess were accurately located.... This setup procedure looks like this....



I used a 3/8" mill to machine the pocket for the larger transfer port, to a depth of 0.125".... That is deep enough to permit using an O-ring to seal it, but not break through into the old velocity adjuster hole.... After milling that pocket, I then rotated the milling attachment 20* about its vertical axis, to angle the new transfer port towards the throat of the valve for better flow.... You have to move the cross slide on the lathe to recenter the port, which is a little tricky because you are now on an angle.... So for the first pass on milling the port I used a 3/16" mill in case I had to make a slight adjustment in the fore-and-aft position relative to the pocket.... In this case I didn't, so I changed to a 7/32" end mill to enlarge the port to its finished size.... Here is a photo just before enlarging the port....



It is important at this stage to mill completely through into the throat of the valve, but not go too deep and hit the other side of the throat.... just use care, and watch what you are doing.... The last step of machining inside the valve is to put the valve back in the chuck and using the 1/2" end mill, face off the front of the plug to exactly 1.800" from the front of the valve.... This will still nicely clear the new 0.219" exhaust port, provided you machined it in the right place, at the 20* angle specified (ie 70* to the valve centerline).... At this point, the inside of the valve looks like this.... Sorry for the poor photo, it is quite difficult to get a clear photo inside the valve....



You will notice that the back face of the exhaust port meets up nicely with the point of the drilled throat.... I will later touch up the inside with a Dremel to smooth any corners.... The next photo shows the new exhaust port from the top.... quite a difference from were we started....



In the next post I will show you the last step in the machining....

Bob

[shorty]

Not sure if your going to pop your valve in a gun and ring it out or give it to someone else but, where ever it ends up it's going to be a great valve.

Almost done with my 25 build and finally getting some numbers. Almost same spec's as yours. Yous is a whole lot better since I am a hack but nearly everything the same except pushing the valve seat forward and angling the exit port.

Thanks for posting here too. I am not a member over at the Guild.

[rsterne]

Here is a photo of the valve with the poppet installed at this stage....



You will notice that the valve stem only sticks out the back of the valve about 0.10".... While that is probably enough lift, I will machine a bit off the back of the valve to allow for more.... If you look inside the exhaust port, on the far side, you will see a grey crescent shape.... That is the epoxy filling the original velocity adjuster hole.... where if we hadn't plugged it, there would be a cavity and a potential leak, above the new plug location.... You will notice that if you machined the transfer port pocket much deeper, you could have broken into that area.... not a good idea.... Anyway, I chucked the front of the valve in the lathe, and turned off the back face about 0.075".... This leaves the LOA of the valve at 2.700", and the valve stem protruding 0.180", so that is the maximum lift.... Although this is less than stock (0.260"), you will NEVER drive the valve that far open, in fact typical lift values run 0.060"-0.120".... Here is the back of the valve, with the poppet installed, showing the finished length....



With the poppet moved forward because of the new valve seat location, the hammer stroke will be increased by 0.150".... This will create more hammer energy and momentum, which will be needed to open the larger throat.... Of course if you are still using a stock MRod hammer, there is a stroke adjustment so you can reduce it if you wish.... I have one more photo for you.... I installed the poppet inside the valve, and took a photo to show just how much clearance there is around it, with the valve drilled out to 1/2"....



As you can see, there is tons of room for flow, nearly 3 times the area of the exhaust port.... All that remains is to clean up the inside of the throat and port and make sure it doesn't leak.... not an easy job without a gun to install it in....  .... shorty, it will be going in my BRod this fall....

Bob

[rsterne]

One more little trick I should mention.... I use this to dress the seat inside the valve, to get it perfectly square to the valve stem hole....



It is a tiny octagon of 400 grit Wet-or-Dry sandpaper, with a 1/8" hole (same size as the valve stem) punched in the middle, with the flats of the octagon a whisker larger than the poppet OD.... On the back of the sandpaper is a piece of double-sided sticky tape to stick it to the sealing face of the poppet without damaging it.... Basically it makes a perfect lapping tool.... You slide it into the valve, the stem sticks out the back, and you grip that with the chuck of a portable electric drill.... Using low speed, pull gently on the drill, run it a few seconds forward, then reverse.... forward then reverse.... 2 or 3 times.... Remove the poppet and check the seat.... You should see a uniform dull area around the throat where it has been sanded.... If there is a gap in the dull area on one side, repeat.... If it's really bad, use a piece of 220 grit first.... You can finish with 600 grit, but I usually jump right to my polishing compound....

I use a metal polish called "Solvol Autosol".... It comes in a tube like a toothpaste tube, and is a white paste with a very fine abrasive in it.... Put a dab on the sealing surface of the poppet, drop it into the valve, and use the electric drill just like with the sandpaper above.... I find it works better on a higher speed, and pulling a bit harder.... A few seconds forward, then a few seconds reversed, and repeat 3-4 times.... Disassemble and inspect both the seat and poppet.... Both should have a shiny line all the way around.... Carefully clean off ALL the grit, assemble, and use the drill to put a final burnish on the parts.... That shiny line all the way around both parts is the indicator that you have a perfect seat.... If it leaks after that, I will be shocked.... particularly after you fire it a few times....

Bob

[aceflier]

Wow! About all I can say.

[LI Airgunner]

Thanks for sharing, I have 2  .25 valves to play with.