Last updated on November 14, 2020
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While working on my new bike I realized that a slightly shorter stem would be good, so I ordered an FSA OS-190 from Price Point. When the box of parts arrived it had been opened (photo), but as the thread locking compound on the screws was unmarred and there were no marks on the stem it appeared to be brand new. Unfortunately, after installing it I found a small crack in the stem cap, right near one of the bolts. Here is a photo of the stem on my new bike, with an arrow pointing to the cracked area.
Having torqued the stem bolts (cap and steerer) to FSA’s published 78 inch-pounds (FSA’s Stem and Post Torque Specs – PDF) I don’t believe this was caused by me during installation. This is also a particularly inopportune place to have a crack, as it could easily lead to stem/bar failure, which would likely result in a pretty bad crash. Even though it was relatively cheap and looks good on the bike when I request to return the item to Price Point I’m tempted to get a different stem, as I don’t want to risk there having been a bad batch.
Currently I’m thinking of a Thomson Elite X4, but now I have to decide on 0° or 10° rise. The aforementioned FSA is 6°, so 10° shouldn’t be too different…
UPDATE: Thinking about it, I wonder if follwing the FSA directions, which I followed, to “[l]ightly grease the bolt threads and under bolt heads” caused the problem. It’s my understanding that greased fasteners, particularly under the heads, are easy to inadvertently over torque, even with a wrench. This is because the fastener slips along much more than normal, and doesn’t provide the resistance that the torque wrench measures.
Hi Steve, when assembling my bike last year I found the torque needed to reach the given value quite incredible. I felt I was going to strip the threads before reaching the recommend value. I greased my bolts as instructed too.
I am using all Race Face components. No cracks as you have, but felt the torque needed was way overkill and have been wondering if it was the grease all along.
BTW, is that phil wood grease?
Rodney Gullett: I agree, it’s probably way more than needed. I’m not completely sure of this, but I think that lubricating the threads essentially makes the fastener pull in deeper for the given torque, resulting in exactly this kind of problem. I’ve got a new stem on the way (Thomson X4 100mm x 90°) and I’m not sure I’ll use the wrench for it or not. Being a completest I’m thinking that I will, but I’ll be VERY certain not to grease under the heads.
That grease there is actually Park Tool PolyLube 1000 which also happens to be green like the Phil’s stuff. I’ve been using it since I started biking a couple years ago and so far it’s been great. One tube only costs $5 or so, is flexible enough to use outdoor in winter, lasts quite a while, and does what it claims. It’s also fairly easy to clean up while new, so any spillage isn’t an issue. I’d definitely recommend giving it a go if you’re needing more grease.
The chapter on threaded fasteners in my machine design text (Shirley-a classic) states that all threads must be clean and lubricated to apply accurate torque during assembly. The screw pulls the parts together by acting like a very stiff spring. It is stretched under tension. Friction in the thread also puts a twist in the screw, which adds a secondary stress. Lubrication will allow any twisting stress in the screw to be relieved after assembly due to normal vibration and load cycles. If a threaded joint is designed correctly and is assembled to the proper torque, if the screw does not fail during assembly, it will never fail in service.
Bottom line: always lubricate threads.