The problem with putting a Marauder trigger in a Disco

[lloyd-ss]

The Situation:
This might have already been covered, but if it has a lot of folks have missed it, me included.
Rumor has it that the very nice Marauder trigger is a drop-in replacement for the plastic trigger in the Disco.  Except for the trigger guard, that is.
Well, it is kind of a drop-in replacement, but not always, and not really.
The Story:
I have a disco that has a history of complaints about the bolt and hammer: hammer binds up, works sometimes, but not always,  hammer pin bends, crappy Crosman quality, bolt is very hard to pull back...not always, just sometimes, hammer is too loose, hammer is too tight. You name it!
Well, come to find out, none of that is true.  Yes, the symptoms are there, but the diagnosis is wrong. 
I like to systematically disassemble the "problem item" until I either find the problem or it goes away. If it goes away, I still like to find out what it was. I had the breech and barrel off the disco and was sliding the hammer back and forth in the tube.  It slid like glass, then all of a sudden it bound up..bad! It felt like real bad "sear drag." And that is exactly what it was, the sear was just marginally dropping out of the way of the hammer, and that one time it really didn't clear, and bound up instead.
So I took the trigger off of the tube to study it.  The first stage was totally adjusted out of it. This was an M-rod trigger, BTW.  And when the tip of the sear dropped down to clear the hammer, the tip tended to get jammed in an inside radius of the trigger link. Very odd.  Maybe this trigger link investment casting had less clearance in the inside radius, causing the forced jam.
The Real Problem:
Then it dawned on me.  I had recently shortened an M-rod air tube and its wall thickness is .095".  The Disco air tube has a .063 wall. One third thinner! So when you install an Mrod trigger into a Dicso tube, the sear sticks farther into the tube and engages the hammer by .032" more than in an M-rod.  That is TWICE as much engagement.    Apparently, 99% of the Mrod triggers have enough extra sear travel to work in a Disco tube. But this one didn't. 
Still, even on a good day, the doubled engagement is not a good thing. But the drop-away design is very forgiving.
The Conclusion
The Mrod trigger usually works very well in the Disco, but not always, and is probably very safe.  But the Mrod trigger was designed to fit a tube with a 50% thicker wall.  So the binding problems have nothing to do with Crosman quality, its just that we all take the interchangeability of Crosman parts for granted, and it doesn't always work.

Sorry for the long winded nature of the post, but I got on a roll!  I hope it helps someone with their "binding issue".
Lloyd-ss

[amb5500c]

Very good post Lloyd.
Richard

[lloyd-ss]

Richard,
Thank you.  I know the M-rod trigger has been put in hundreds of Discos without a hitch, and that is fine.  It's just that the trigger is such a critical element, that we need to give it some thought before we change it.
Lloyd-ss

[JBird]

Very informative for us do-it-your-selfers.  Thank you!

[rsterne]

I'm wondering if that thinner wall, and the corresponding lack of clearance for the sear could be the reason for the few shattered sears reported with MRod triggers on Discos.... I had the first one shatter on my MRod trigger on my Hayabusa.... and it has a 0.065" wall tube.... I chalked it up to the (rear portion of the) waist in the middle of my hammer impacting the sear.... and I think that was the culprit.... but perhaps it wouldn't have happened except for the clearance issue.... Come to think of it, I do recall there were times it was hard to cock.... Hmmmmmmmmmm.... looks like we should be shortening the top of the sear a bit when installing the MRod trigger in a Disco....

Bob

[lloyd-ss]

Bob, I was thinking more of a .032 thick shim between the trigger assy and the tube. I don't know if the sear is through hardened, or just case hardened, so grinding might or might not be an option.  By using a shim, you could also later swap the trigger back to an M-rod if need be.
Lloyd

[rsterne]

My broken sear actually looks "cast" in appearance.... I think it may be sintered metal....

Bob

[1377x]

would this go for the maurader pistol trigger group too? i guess not because the maurader pistol trigger group doesnt work in the marauder
would making another sear with the proper clearance out of stainless steel be a good idea?
now this is kind of still on topic it has to do woth the marauder pistol trigger group in the 1377
i dont know if the wall thickness is the same as a 2xxx or disco.if the 1377 wall is thinner then it would be the same problem as first described
i have heard a lot of sear drag stories from users of this set up
guess i have some homework to do
thanks for posting

[lloyd-ss]

I don't have a 1377 to measure the wall thickness, but it looks like all the 2xxx, Disco tubes, and the Marauder PISTOL, basically everything with a 7/8" diameter tubes, all have a nominal .063 wall thickness.  Those all swap around fine.  But the 1-1/4" diameter Marauder rifle tube has the 50% thicker .095 wall.  So the problem should be confined to using the Marauder Rifle trigger in the 7/8" diameter tubes.
Has anyone heard differently???

Stay tuned today for the upcoming , "The Solution."

Lloyd-ss

[PakProtector]

Bob, I was thinking more of a .032 thick shim between the trigger assy and the tube. I don't know if the sear is through hardened, or just case hardened, so grinding might or might not be an option.  By using a shim, you could also later swap the trigger back to an M-rod if need be.
Lloyd

Lloyd, I bet anything over .015" thick would do an adequate job here. And if you want to go with .031 exactly take a set of feeler blades( sourced inexpensively, say HF ) and cut the end with a hole off. The .015 and .016 for one shim, and .014 and .017 for the other. The usual pivot bolt size is very close to that of the bolt that is holding the trigger on.
cheers,
Douglas

[rsterne]

Using the PRod trigger group on a 13XX has a different problem.... The wall thickness of the tubing is the same (0.065") but the OD is smaller and it fits deeper into the groove in the top of the trigger.... This means the sear hits the tube in front of the sear slot.... You have to either lengthen the slot or file a flat in the top of the tube for it to clear or the gun won't cock....

Bob

[lloyd-ss]

The Solution

I made a .032 thick shim to properly space the Marauder trigger out from the .065 wall of the Discovery and the 2xxx 7/8" dia tubes.  You can barely see it between the trigger and the tube.  The trigger now functions just like it does on the Marauder, with no snagging binding or mysterious breakages.
I am going to put a post about this in the GTA Vendor gate in the Airgun Lab and will probably make a few of these for folks who are interested.
Lloyd-ss

[MustangMike]

hmm never had a problem like that with my mrod trigger and disco setup but its nice to know gil's problem has been id'ed and fixed.


depending on price id take one, but would this spacer work with a challenger hammer ? does the challenger/prod hammer change anything ?

[lloyd-ss]

hmm never had a problem like that with my mrod trigger and disco setup but its nice to know gil's problem has been id'ed and fixed.


depending on price id take one, but would this spacer work with a challenger hammer ? does the challenger/prod hammer change anything ?

Mike,
Like I said earlier, there are a lot of M-rod triggers on Discos that aren't having a problem.  The tolerances on the one I was working on just seem to have stacked up in the "plus material" direction, and it was fairly easy to replicate the interference problem that had been described.  I have to say that adding the spacer does seem to give the trigger a better release.
It should work fine with the challenger hammer, too.  The hammer-sear interface is the same.
Lloyd-ss

[rsterne]

Very nice job, Lloyd.... a product I didn't even know I needed.... Aluminum?....

Bob

[gene_sc]

Great post Lloyd. And  I have made at least a half dozen M-Rod to Disco trigger mods. In testing I never have run into the issue you posted but thanks to you I know what to do if it ever happens. I have some  plasctic sheet stock that would work just as well as the aluminum. Great idea bud.
Gene

[jimmie lee]

Decent of you to post this Lloyd as it takes the heat off Crossman and gets to the meat or lack thereof of the air tube wall thickness difference. Productive post.

[Sqrl Klr]

Deleted. Just saw Lloyd's follow up solution post. Thanks Lloyd.

its nice to know gil's problem has been id'ed and fixed.

Boy you got that right! 3 months of issues I couldn't resolve and $1400 wasted on a gun I couldn't get to work. Being new to pcp and going through this with my first pcp I had lost my love for the dark side because of it all. Now Lloyd has brought me joy again and it will be such a thrill to shoot it without issues now. You don't know how wonderful it will feel to shoot it with confidence now knowing a issue will not pop up anymore like it always has been from day one before I ever did anything to it. Lloyd I hope this shows you the gratitude I have for you. So appreciated.

[MustangMike]

gil

dude i told you it was a funky issue that i hadnt heard of before. to be honest lol i kind of thought maybe you needed a nap or had a long day or something and that the problem was just you.. no offense intended, but it is now documented and solved

[lloyd-ss]

Sqrl Klr,
Thank you very much, and I am glad you sent it to me, and that I was able to help. If I hadn't just recently cut off that Marauder air tube, I might have missed this one. 
Lloyd