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I had to adjust a handle bar of an older road bike I want to start using again. When unscrewing the handle bar to stem bolts I noticed that the washers had grinded into the aluminium already. As I had to readjust the handle bar a few times this got only worse to the point that the washers were already deforming and locking on the screws. I fixed that gently with a pipe wrench and finally reassembled everything back together with proper fit and almost equal gaps. Is the worn material or now slightly different fit of the screws of any safety issue or could it lead to any or is it just a cosmetic thing? By the way I only used a really light torque of 4 Nm.

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Damage to the faceplate from the washers digging into or not being present at all when tightening is pretty common and not an issue unless taken to an extreme.

If the washers are mangled and not functional, it can be good to replace them. It might also work to re-orient them and/or put some grease between the bolt shoulder and the washer.

Don't undertighten the stem bolts. That's even more true if the washers aren't doing their thing; when they're staying put properly and act as the bearing surface for the bolt shoulder, they increase the clamping force for a given torque input, which means that for the same given torque input there will be typically be less clamping force if they're rotating under force and digging into the faceplate. If you can't stop them from doing that then use normal torque and grease both sides of the washer.

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    Thanks for your answer! To me it seems that the bolts are still fitting decently. I thought 4 Nm and using grease would suffice. I also thoroughly checked that the handlebar doesn't move after installation. Unfortunately there is no spec on the stem. When disassembling I tried to find the original torque via loosening one bold a bit and incrementally applying more torque until the screw moved a bit again. This way I figured original torque had to be around 4 Nm. Would you go higher?
    – conste
    Jun 30 at 23:46
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    @conste There have been a few stems that use 4 Nm but not many, and they've mostly been very high end and/or used M4 bolts (Ritchey WCS 260, Thomson). For most common stems with M5 threads and 4mm hex cap fittings, use 5-6 Nm as a generic number. Jun 30 at 23:55
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    The washers are there to stop the bolt heads from doing the same, and spreading the load. I would either replace the washers or flatten the existing ones, and give them a quick sand to remove any sharp corners or high spots. Thicker washers would not go amiss here.
    – Criggie
    Jul 1 at 2:02

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