Stihl's new style fastener

[HarleyT]

Tearing down a new MS251, I came across something new on the cylinder bolts.
The tips are "pointy, and the threads don't start right away...
Nothing controversial, just interesting.

 

[LogSawyer74]

Self cutting threads maybe?? Wonder how that would hold up after removing the cylinder a few times?

 

[kybob]

I think it helps on quicker installation at the factory without cross threading.


Sent from my iPhone using Tapatalk

 

[RED-85-Z51]

Pretty coarse thread too by the looks of it.

Sent from my SM-G996U using Tapatalk

 

[grizz55chev]

Tearing down a new MS251, I came across something new on the cylinder bolts.
The tips are "pointy, and the threads don't start right away...
Nothing controversial, just interesting.

View attachment 896594

Was there thread locker on it when removed?

 

[ironman_gq]

Do they thread into plastic or metal?

 

[HarleyT]

Here is their location.

 

[ironman_gq]

Definitely look like thread forming screws. Basically no chance of cross threading as the screw forms it's own as it's driven in and they are very resistant to loosening up. They don't cut the threads they form them in the cylinder material and are basically self locking once torqued down.

 

[PV Hiker]

Wonder since they come up through the case they are designed to help locate and center preventing cross threading.

Faster factory assembly without buggering up threads the more they can produce.

 

[Wood Doctor]

You have to wonder how many times Stihl tested this design. See post #2. I suppose they assumed that every time the screw is used, it's going into a new cylinder and cutting new threads. That's a rather powerful assumption in my book.

 

[ironman_gq]

You have to wonder how many times Stihl tested this design. See post #2. I suppose they assumed that every time the screw is used, it's going into a new cylinder and cutting new threads. That's a rather powerful assumption in my book.

It doesn’t cut them, it forms them. Basically mushes the metal around the threads and shank. Once they’re formed the screw works just like any other, it won’t recut new threads once they’re formed

 

[Wood Doctor]

It doesn’t cut them, it forms them. Basically mushes the metal around the threads and shank. Once they’re formed the screw works just like any other, it won’t recut new threads once they’re formed

That's good to know. Seems to me that forming is the same as cutting, but I hate to be picky. I have a feeling these will work out OK and I imagine they have been tested to high heaven. Nice to jaw with another 361 owner. It remains my favorite saw even if its carb does flood occasionally.

 

[kybob]

Yes on thread forming taps ( or screws )
I had one in my too box for years. It was a 3/8-32 TPI. For forming fine threads in brass or aluminum. It was the first fluteless taps I’ve ever seen. Looked like a pointy bolt.


Sent from my iPhone using Tapatalk

 

[L34]

Would they have to be put back in the same hole as removed from?

 

[Wood Doctor]

The idea behind the threads on the screw starting back from the point is that the screw will then self-center and tend not to form a cross thread when used again in the same hole where threads have already been cut (formed) before. Power drive tools may have prompted this idea. I personally do not use power drive tools when setting cylinders back inro the case.

 

[kybob]

Would they have to be put back in the same hole as removed from?

Some say it doesn’t matter, but I always try to put every bolt back where it came from. Might not make a difference all the time, but I know sometimes it does.


Sent from my iPhone using Tapatalk

 

[kybob]

Using power drives on fasteners , especially in aluminum or magnesium, can get you in trouble pretty quick.
Cross thread, stripped threads, twist bolts or screws off. I just do it the old slow way. And considering you don’t damage anything, it can be faster in the long run.


Sent from my iPhone using Tapatalk

 

[dmb2613]

They have had that type screw on clamshells for years so they are tried and true. The old ones just had threads all the way to the tip, but were self tapping too.

 

[Wood Doctor]

They have had that type screw on clamshells for years so they are tried and true. The old ones just had threads all the way to the tip, but were self tapping too.

Correct: Pan head self tapping screw, D6 x 52 (both the MS290 and 029):

 

[ironman_gq]

That's good to know. Seems to me that forming is the same as cutting, but I hate to be picky. I have a feeling these will work out OK and I imagine they have been tested to high heaven. Nice to jaw with another 361 owner. It remains my favorite saw even if its carb does flood occasionally.

The big difference is that a cut thread is made by removing material. A formed thread doesn’t remove any material, it just moves it around, in this case the aluminum gets extruded toward the shank of the screw and fills the gap between the threads