Using a Shorter Stem Bolt?

[PsyDoc]

I've been a mostly a lurker here for a few years and am getting back to being a roadie after being hit by a car five years ago. Anyway, I am replacing my Ritchey stem bolts with titanium ones. The faceplate bolts are M5x16mm. The stem bolts are M5x18mm. I wasn't paying attention when I ordered them and I didn't notice that the M5x18mm did not come with a washer. What would be the concern, if any, to using the M5x16mm for the stem bolts as well? When torqued to 4nm, the orginal Ritchey stem bolts stick out a hair.

[pdlpsher1]

It will work but for maximum strength you need the 18mm length. This is especially true when you are replacing steel bolts with Ti bolts, since Ti bolts are half the strength of steel bolts.


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[alcatraz]

Whats the percentage of available threads that the titanium bolts thread into fully torqued? If it's nearly through I wouldn't worry. If we are talking 50% then that's way under what the stem manufacturer intended.

If you are a heavy guy that likes to drive over potholes and cobblestones like a tank then I would of course take extra precaution here.

/a

[PsyDoc]

I'm 65kg and don't torque the bars when riding. I thought I read somewhere that ti bolts are nearly as strong as steel bolts, until you get to the high-tensile steel bolts. Thank you for the replies.

[darnellrm]

From an engineering standpoint, the first 3 threaded bear the vast majority of the load, so as long as you have 3+ threads engaged, you should be fine.

[Frankie - B]

darnellrm, thanks for the best answer in this thread. It looks like the others were just guessing.

[kode54]

i would opt for 6 turns on the bolt. on some of the failures i've had with stem bolts (mostly titanium) they would shear at the head of the bolt. and that's using a torque wrench to 5nm with carbon paste. bad bolt. ony happened twice on a 3T stem with supplied bolts.

[darnellrm]

i would opt for 6 turns on the bolt. on some of the failures i've had with stem bolts (mostly titanium) they would shear at the head of the bolt. and that's using a torque wrench to 5nm with carbon paste. bad bolt. ony happened twice on a 3T stem with supplied bolts.

You have some kind of other issue going on ( bad bolts, bad torque wrench, etc ). Besides, if the bolt is going to shear at the head, what difference would it make how many turns you did on the bolt??

[mattr]

From an engineering standpoint, the first 3 threaded bear the vast majority of the load, so as long as you have 3+ threads engaged, you should be fine.

Yeah, i almost posted that and then deleted it, as its generally for decent threads in a suitable material (usually steel). Multiply tightened aluminium stems with a dubious level of quality and unknown tolerances and the risk of over (or under) tightening........... Makes me nervous.

(I've had a bolt pop out of a high quality stem with the aluminium threads still attached. And that was only tightened (barely) to spec. I'd only ridden the thing half a dozen times.)

[darnellrm]

True, but you can't really make suggestions for sub-standard products. How about = "always make sure the screw goes all the way through and put a nut on the back side" ?

[MyM3Coupe]

From an engineering standpoint, the first 3 threaded bear the vast majority of the load, so as long as you have 3+ threads engaged, you should be fine.

Yes they do. And I've done hundreds of thread engagement calculations as an engineer for a large DOD company.

[alcatraz]

I've had a bolt pop out of a high quality stem with the aluminium threads still attached. And that was only tightened (barely) to spec. I'd only ridden the thing half a dozen times.

Sounds like a bad design (threads too short) or manufacturing defect. What do you think the reason was?

What stem was it?

For the OP I just'd like to add...

If a manufacturer wants to use a softer stem material or a material more prone to fatigue they'd better design the threaded part deeper.

A rule saying 3 threads is enough is a bit oversimplified.

If the stem is steel or something else solid then you don't need as many threads.

/a

[mattr]

Sounds like a bad design (threads too short) or manufacturing defect. What do you think the reason was?

What stem was it?

Bontrager.
No idea why, the metal i picked out of the bolt threads was fully formed, almost like a helicoil.

True, but you can't really make suggestions for sub-standard products. How about = "always make sure the screw goes all the way through and put a nut on the back side" ?

Yeah, but the 3 threads is only really applicable in certain, very specific and controlled cases. As soon as you move away from that, you start to have issues.

[enzomavic]

No worry
It will work