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Fixing the Dreaded Marlin Jam
by Rusty Marlin

Thanks to Rusty Marlin for this article.  

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Disclaimer:  This article is for entertainment only and is not to be used in lieu of a qualified gunsmith.  Please defer all firearms work to a qualified gunsmith.  Any loads mentioned in this article are my loads for my guns and have been carefully worked up using established guidelines and special tools.  The author assumes no responsibility or liability for use of these loads, or use or misuse of this article.  Please note that I am not a professional gunsmith, just a shooting enthusiast and hobbyist, as well as a tinkerer.  This article explains work that I performed to my guns without the assistance of a qualified gunsmith.  Some procedures described in this article require special tools and cannot/should not be performed without them.

Warning:  Disassembling and tinkering with your firearm may void the warranty.  I claim no responsibility for use or misuse of this article.  Again, this article is for entertainment purposes only!

Tools and firearms are the trademark/service mark or registered trademark of their respective manufacturers.


The Problem
The "Marlin Jam" as it is affectionately known is caused by an inherent design/manufacturing flaw of the Marlin lever. The lever has a snail shaped cam surface that goes around the pivot screw. This snail shaped cam rides on a sloped surface on the bottom of the carrier and raises the carrier enough to allow the first incoming shell into the carrier and to block the next incoming round from jamming up the works. Every time the lever is cycled the carrier bounces on the forward edge of the cam. The forward most edge of this cam is left sharp at the factory (the flaw).

The bouncing forges a notch into the bottom of the carriers' slide surface and over time (high number of cycles) lowers the carriers' initial pick-up height allowing the rim of the next incoming shell to slip over the front and jam it up tight. Note the notch labeled 'A' and marked with an arrow in the photo.


  
Simply changing the carrier out as many repair places do is only a temporary fix at best. The new carrier will get a notch forged into it from the sharp edge of the lever cam and over time will settle downward in the action and again give you the ďMarlin JamĒ. Following the steps below will cure this problem FOREVER.

The Cure for New Guns
With new guns (less than 50 cycles) you can generally get away with just putting a radius on the forward edge of the lever cam. While this will lower the initial pick-up height slightly, it typically will still be high enough to prevent the dreaded "Marlin Jam" from ever occurring. If your rifle jams you will need to follow the steps outlined above.

Many of you will have guns that jam once in awhile but haven't figured out why. You probably have an odd piece of brass or two in your collection. For example the gun might run fine on Starline or Winchester but lock up tight on R-P. R-Ps are slightly smaller than others and this will cause the problem to be sporadic. Eventually the gun will jam on anything you feed it and you will need this fix.

The Fix for Used Guns
Three things are required to fix the problem. The first two prevent it from ever occurring again and the third retimes the carrier to proper height. Donít even bother to do them if you arenít going to do item 2A or item 3.

1) Put a generous radius on the front edge of the snail cam on the lever. I use between a .025 and .035" R. This radius spreads the load out from the force of the carrier bounce and prevents the forged notch from reoccurring. You will notice a shiny line will form but it wonít be a notch like before. The large radius also self limits how deep it can forge into the softer carrier.

2A) Order a new carrier from Marlin. If you do this, you will be done, otherwise, read on...

2) Grind the slip cam surface on the carrier to just remove the forged notch.
These two items will make the problem worse until item three is done.

3) Bend the carriers' nose up about .05".

Use the heat and bend method described below.

Clamp the carrier in a large bench vice so the pivot hole axis runs vertically. The two parallel faces at the pivot hole end need to be clamped in aluminum blocks for a heat sink. If the heat gets to the plunger spring you will need a new carrier, so the heat sinks are very important.

Heat the neck just behind the front of the carrier till dull red. Position a block of steel (or brass) just behind the shell stop (tang that hangs down in front) and tap the head "up". This is actually going to be parallel to the floor.

Measuring this movement can be difficult. I gave up trying after the first few and now itís by eye. After cooling try it in the gun. If you went too far the very first incoming shell will jam as the lever is opened; the carrier will wedge it up against the top of the magazine opening. You will need to heat the carrier again and tap it back a touch. This retimes the carriers' initial pick up height to let one round in and keep the rest in the magazine.

Rusty Marlin, SASS #33284

 
   © Copyright 2008 Roy Seifert.