Canadian Airgun Forum

Help with a Crosman 451 stem and seat assembly problem.
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Author:  R-Gun Pete [ Sat Oct 22, 2016 7:36 pm ]
Post subject:  Help with a Crosman 451 stem and seat assembly problem.

I purchase another 451 but this one has a leak.

After disassembling it, I discovered that the face seal was hard and dry. I had to pick it out piece by piece since it was crumbling.


In the past I was successful in making face seal with the plastic of coffee can cover.

In this case the cavity was fairly deep so I placed one plastic layer, one leather layer and two other plastic layers. The problem is that the shaft is larger at the middle so the seal parts had to be streched.


Unfortunately, it failed so I had to reopen the pistol and remove the pieces.


Looking more closely I saw that there was a spring pin, I thought that if I remove it I would be able to separate the cup from the stem and make a nylon cylinder that could be drilled and placed in the cup before reinserting the stem.



Again, nothing is simple, after the pin was out the stem didn't want to get out.

I heated the brass cup with a heat gun and try to punch out the stem without any positive result.

Anybody have an idea on how to tackle the problem?

Thanks for reading.

R-Gun Pete

Author:  Gippeto [ Sat Oct 22, 2016 8:44 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Looks a bit of a bugger to make a complete new one, so would suggest something along these lines...gently used to avoid damaging the parts of course.


Otherwise....Len may have a better idea. Can get hold of him over here;


Author:  Ace [ Sat Oct 22, 2016 10:34 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

cant remember now but did that shaft screw off after removing the pin

Author:  R-Gun Pete [ Sun Oct 23, 2016 7:43 am ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Hi Gippeto and Ace!

Thanks for the info.

Because of the locking pin, I thought that it could be threaded as Ace suggested but I couldn't see any thread start and after wrapping the stem in a rubber sheet and tried to turn the cup with a wrench nothing moved.

Not having a contraption as shown by Gippeto, I saw that some people were heating the brass and pushing the pin out. I also tried that and it didn't move again.

Having failed with my first sealing attempt with my plastic layers, I wanted to separate the components to be able to insert a nylon or teflon cylinder. This option was not available since I couldn't get them apart.

Furthermore, I discovered that the cup didn't seem perpendicular to the axis of the stem. I couldn't figure how it could have happened since I use a piece of wood with a small hole for the stem. The brass cup was sitting square on the face when I tried to punch out the shaft so it shouldn't have done that.

Anyway I tried to straighten it. This pin (because it is fairly long) is not very stiff and was bending all over the place. I got it worse to the point that it didn't want to slide ithevalve body.

I placed it in the chuck of my press drill and it was wobbling like crazy. Slowly I was able to make it nearly straight and it was now sliding in the valve body.

Then I realized when I had messed up. During my tryout with my plastic disks approach, due to the streching to get them over the larger diameter, the surface was not as smooth as the other timeswhen I used the technique. Normally I also lightly tap the stem with the face seal against the valve seat to get a nice groove. The bending probably occured when I did the tapping. The stem is deep in the valve body and I used. 3/8" dowel (smaller than the cavity) and I was possibly off centre when I smacked it. Looking back at the picture with the yellow seal I can now see that the groove is not concentric.

I made a drawing of the part and I will try to make a new one. For the time being, I decided to make a face seal by pouring a semi-liquid substance as Goop and formed it with my wet finger.

When it started to cured and was not sticky but still soft, I pushed it in the valve body to make the imprint.

This morning I reassembled everything and pressurized it . There was a slight hiss for a little while but it stopped. When I tried to fire the airgun nothing happened.

When I made the imprint some material flowed around the stem base and I thought that it would help the seal so I left it. Now I realized that I should have trim this excess to keep the whole seal at the same level. That ridge is probably still blocking the airflow when the firing is hit and moved back.

What a mess. On the part list it was $2.70 for the stem seat assembly, I would have purchase one in a blink of an eye if it would have been available.

Anyway, it is enough for today. As a last resort I maybe try to reopen the pistol and shave the excess to see if it would work.

Sometime learning is a bit painful.

R-Gun Pete

Author:  Gippeto [ Sun Oct 23, 2016 9:24 am ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Will have a look at making a stem for you if you pm the drawing. Have some ptfe that I would use for the sealing face.


Author:  R-Gun Pete [ Sun Oct 23, 2016 5:58 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Hi Gipetto!

Sorry for the late reply.

I was helping my son with a poster presentation and after I had a shooting session with a friend to change my mind.

When I showed him the result of my weekend he offered to make me a replacement.

After checking the post on CAF, I saw that you offered me to make one too.

I have two 451 so I think I will go with my friend's offer and if everything turns to work well I will end up with a set of drawing that would be 100% good.

If your offer is still valid at that time we could discuss how to proceed.

Thanks again.

R-Gun Pete

Author:  Gippeto [ Sun Oct 23, 2016 7:49 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Good to have friends. :)


Author:  KEN. [ Fri Oct 28, 2016 10:19 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Why don't you try and get a rebuilt V/V stem from Rick Willnecker at Precision Pellet..USA....
He should have what you want....KEN.

Author:  R-Gun Pete [ Sat Oct 29, 2016 2:25 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Hi Ken!

I haven't exhausted all my options yet.

One of my friend is trying to make me a replacement stem and seat that could easily be separated when it is time to change a face seal.

In the meanwhile I have straightened the original stem and I am exploring how to make a seal that could fit in the cup without dissassembly.

I am thinking of making one in plastic in 3 pieces using a rapid prototype printer.

Unfortunately i couldn't get those parts for the weekend and I looked at other possiblities like melting plastic in the cup.

The plastic of a coffee can cover can be melted using a heat gun, the problem is to control the flow to direct it in the cup.

So at some point I thought of glue gun. After the cup was filled the surface was a bit uneven so with the heat gun I brought it back to practically a jelly and spun it in my press drill.

I obtained a very smooth surface so I reassemble the pistol for a tryout and it was another failure.

The material is not hard enough. I guess I will have to wait for my friends to finish machining the replacement stem before giving up.

So, Ken, thanks for the info because I might need it.

R-Gun Pete

Author:  ColdAir [ Sat Oct 29, 2016 2:57 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

JG Airguns has the CRS451-099 Valve Stem as well. $40 USD plus shipping. 54 other parts stocked for the 451 as well.


Author:  R-Gun Pete [ Sat Oct 29, 2016 5:45 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Hi ColdAir!

It seems that the items were added in 2008. I am not sure if they will still be available.

Furthermore it seems the stem/seat assembly is an original (then with the dried out seal) which might gave me the same problem as mine.

If I want to use the original I need to separate both part so it would be easy to insert a new seal or find a plastic hard enough that can be moulded in situ.

Thanks for the info I will keep an eye open.

R-Gun Pete

Author:  KEN. [ Sat Oct 29, 2016 11:26 pm ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

The valve stem holds the seal in position and needs to come out, then the seal is installed and stem pressed or screwed back in. If you call Rick Willnecker he should be able help you...If it was me I'd just get a V/v stem from him....he might sell you some seals that fit most of the other Crosman's
as well...All these stems must come out for proper seal replacement. Sometimes you have to remove the brass lip as they can be .peened over on the edge.of the brass cup...I usually press the stem out then chuck the brass into the lathe and use an end mill to remove the brass edge and seal. ......KEN.

Author:  R-Gun Pete [ Sun Oct 30, 2016 8:18 am ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Hi Ken!

I realize that the best course of action would be to separate the stem from the brass cup but this is where it fails. There is a small spring pin locking both components together but once removed I cannot go further. It doesn't unscrew or slide out.

I am waiting for my friend to complete the machining of the parts (hopefully in the next few days). If it still fails I will contact Rick Willnecker.

I know that it might seem foolish but my first goal when working with vintage airguns is to find a way to fix it myself with stuff in my environment. This would ensure that it could be fixed again in the future if needs be.

My options are quickly running out so I will know soon if the parts should be ordered from Rick.


R-Gun Pete

Author:  KEN. [ Tue Nov 01, 2016 1:05 am ]
Post subject:  Re: Help with a Crosman 451 stem and seat assembly problem.

Good luck with that...KEN.

Author:  R-Gun Pete [ Mon Nov 07, 2016 12:01 pm ]
Post subject:  Crosman 451 stem/seat assembly problem. (SOLVED)

My problem is finally solved.

My friend was able to make my parts and I reassembled the pistol over the weekend.

When he offered to machine the pieces on his full size lathe he didn’t realized how small they were. He is an engineer and not a machinist but he likes to tackle different projects and he thought that it would be a good practice for him.

He fabricated the parts from my drawings but unfortunately I made some design mistakes that would be corrected if another set should be made at a later time.

I was fixated on replicating the original parts but, at the same time, keeping the option to have an “easy” disassembly of the Stem/Seat assembly.

My first approach was to have a thread but being that small I didn’t want my friend to struggle with that so I opted for a sliding fit with a cross pin.

The brass seat needs to have some flats to let the CO2 flows to the face seal where it will be stopped. I made a quick fixture to hold the small brass piece so I can make the flats on a belt sander.


My indexing was not perfect as I did it by eye and I made the perpendicularity correction by hand with a file. My measurements on flats are within the specs I needed.


The following picture shows the newly machined parts beside the original Stem/Seat assembly. There is a bit of shatter marks on the firing pin side but as it was already at the right size trying to smooth the finish would bring it undersized. I decided to just rub sandpaper on it to attenuate any sharpness and put silicone grease on the shaft (thinking that it will be kept captive in the tiny grooves and hoping that it would help to seal).


The valve block on the 451 is a large piece of brass and it is difficult to see inside so guessing where it is sealing is exactly that, guess work. I was assuming that the larger diameter after the firing pin would rest on a shoulder in the block when the face seal was against the valve seat in the block. I should have thought about it more carefully as to try to achieve 2 simultaneous contact points would make practically impossible tolerances.

Being in a hurry to try my parts, this assumption got me in trouble. This train of thought made me sure that the shaft would have nowhere to go, being sandwiched between the spring pushing on the back of the small brass cup and the contact surface of the larger diameter on the firing pin. The cross pin was then not necessary.


… but I discovered it only after reassembly and pressurization. When the face of the plastic seal is sitting against the seat of the valve the larger diameter on the stem is not touching the shoulder in the passage. There is probably enough room to allow for the plastic seal to wear and, in this case, the shoulder is contacted before damage could happen to the valve seat in the block.
Based on my assumption I used red Loctite to hole the shaft in place and as a sealer. Not being a product that I normally use, I applied it and let it cure for about an hour. This is not long enough, I know it now.

After pressurization, I had a leak that could be felt through the barrel so it was effectively coming from the seat seal area but firing the gun was doing funny things. The hissing sound was noticeably less when the hammer was resting on the firing pin than when it was cocked. This mean the pin was moving and the leak was around the sliding fit in the brass cup. Effectively, after disassembly, the Loctite was all around the plastic seal in the cup. I had to take everything apart and clean everything again to make sure that no particles had travelled in the valve body.
This time I reassembled the Stem, Seal and Brass Cup with Loctite and put it aside for more than 36 hours.

In the meanwhile, it is not because the main hissing was coming from around the stem that I didn’t have other potential sources of leakage. To minimize the possibilities I checked the valve seat in the large block. It seems that I was seeing some tiny marks as shown in the picture below.


Not looking forward to another assembly/disassembly cycle in case of failure, I decided to make a tool to polish the valve seat. I had to shave the diameter of one end section of a ½” plastic rod in order to reach deep enough in the hole. With a punch I made disks of 400 and 600 grits that were attached to the tip with double faced tape.

I rubbed it by hand until it looks smooth as shown in the next picture.


Finally, to be sure that the stem would not go anywhere I installed a cross pin that was also positioned and sealed with Loctite. I should have checked my picture before reassembly because the region I wanted to show is a bit blurry.


This time it is a success.

It was pressurized and stayed silent so I fired the gun and the blowback worked perfectly so I moved in my garage and proceed to shoot 30 pellets then I stopped and left the residual pressure for several hours.

When my friend came for our shooting session, I let him shoot the pistol; there was still enough pressure for another 2 shots. At this point, I removed the CO2 cartridge and reinstalled a fresh one. We got 34 good shots before it stopped recocking (which is about the same that my other 451).

I stored it overnight with pressure in it and when I shot it this morning it was still holding. I will continue to do that tonight and tomorrow.

I am feeling confident that it is now fully functional.

As for the changes in the design, I would make the cup with a blind hole, leave a precision sliding fit on the stem and keep the cross pin. Here only the small cross pin would need to have Loctite to keep it in place and seal it. The opposite side to the cup side in the brass part being intact; there would be no chance of leak.

I am also exploring a couple of other approaches with rapid prototype printers. I would like to know if the plastic from those machines might be a candidate for sealing material.

For the first, I have designed a 3 pieces set to be tried on the original stem that I couldn’t take apart. The intent would be to have two small half tubes placed around the stem under the lip and a larger tube that will slide around them and lock everything in place.

For the second, I remembered that stem replacements for some Crosman models are only a steel pin with a larger plastic head that is also the face seal. In those the brass cup doesn’t exist so I was thinking to do the same thing. I will have another stem machined with a thread at the end where the cup should be and, from the rapid prototyper, I will get a plastic replacement with a shape that would combined the brass cup with the seal in place.

I may show the result at another time as it is still a work in progress.

R-Gun Pete

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