Liner lock started to fail! HELP!

[Sansei]

Why would the liner-lock all of a sudden start to fail? My daily carry for the past few years, bm975sbt which has never given me any trouble now closes when there is even slight pressure on the back of the blade. Any ideas on how to fix? Everything is tight and the been no abuse out of the ordnary.

Thanks.

 

[Professor]

Greetings. Let me see if I can be of any help, and get some questions out of the way.

When you say fail, how do you mean exactly? It sounds as though the liner hasn't worn its way all the way across, but rather is "popping out of gear" when spinewhacked? Is this the case? What exactly is the position of the liner bar across the blade tang(25%, 50%, etc. from the left)?

Professor.

 

[A T Barr]

The spinewhack should take care of that. Be sure and protect yourself from that blade popping back. I always hold a large piece of plastic in my left hand and cover my knuckles of my right hand, when I spinewhack my knives. And, I spinewhack each knife I make, before I ship it out. If that does not do it, then send the knife back to Benchmade to correct.

------------------
A.T.
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[Costas]

I had a big name folder "slipping out of gear", because the liner had polished the "ramp" of the blade. I disassembled the knife and used a piece of coarse sandpaper to "scratch" the ramp. This made it rough again, so the liner does not slip anymore (but I need to take care not to let any lube reach this point).

Of course, all this is NOT acceptable for such an expensive, high end production folder, but at least I found the way to cure the problem.

 

[Joe Talmadge]

A liner lock that's been very solid for quite a while, and which does not seem to show any inordinate wear, can nevertheless suddenly start to fail. That's part of my discomfort with that lock format in general.

A.T. was the first one to tell me that the spine whack test can actually "set" the lock, which results in the lock ceasing to fail. He's right, I've seen it work many times. I'd suggest doing exactly what A.T. says: spine whack it to see if you can set it, and ship it back if that doesn't work.

Joe

 

[Esav Benyamin]

<font face="Verdana, Arial" size="2">Originally posted by Sansei:
My daily carry for the past few years, bm975sbt which has never given me any trouble now closes when there is even slight pressure on the back of the blade. </font>

My own BM975SBT never gave me any trouble, scarred up as it is, but I've replaced it with a Vaquero Grande lockback, a Sebenza integral lock, and a BM730 Ares axis lock, depending on the circumsatances -- not all 3 at once! (... why not ...?)

Liner locks are neat but unreliable.

 

[Walt Welch]

The BM97X series of knives had some of the most atrocious locks of the entire BM line. You are lucky that you have gotten this much service out of your knife.

Your best alternative is to send it back to BM. If you decide not to do this, then take the thing apart, degrease all the parts, then lube with a PTFE/oil or PTFE/grease. Pay particular attention to the tang/lock interface. This surface should be well lubed, and smooth. Ti tends to gall, and if you don't have lube on this interface, and it is rough, as described in the above poster's knife, you are asking for a sticky, rapidly wearing liner lock.

I did this to about half a dozen of these knives. Some were then acceptable, but a few remained sticky no matter what I did. None, however, failed the spine whack test.

You should be sure that the pivot pin tension is correct. I had a well made A T Barr knife which failed the spine whack test due to a loose pivot pin; the slack allowed movement of the lock bar.

Hope this helps, Walt

 

[Cliff Stamp]

Walt :

<font face="Verdana, Arial" size="2">Pay particular attention to the tang/lock interface. This surface should be well lubed, and smooth. </font>

If you lubricate the locking surfaces isn't that likely to cause instability?

-Cliff

 

[Walt Welch]

Cliff; this has not been my experience.

I was down at Steve Harvey's place when he performed the spine whack test on my A T Barr folder, and it failed. He cleaned the tang and liner lock bar interface surfaces, and lubed them, which improved, but did not eliminate, the instability of the liner lock. As mentioned above, tightening the pivot pin eliminated the instability (I am glad I didn't send it back to A T!!).

If the Ti liner lock bar and the VERY hard tang are not lubed, the lock is going to be very sticky, and the soft Ti is going to gall itself into early retirement.

Proper geometry and tension on these surfaces will allow for the necessary lubrication. I cannot recall ever seeing a knife from the factory where these surfaces were NOT lubed. It is easy to tell; just close the knife, and look at the tang. You should be able to see the lube. Sebs come with a film of their white PTFE grease on these surfaces.

Hope this helps, and by all means let me know if your experience is different, Cliff.

Walt