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Mercury Mk3 - securing guards

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Magnum3127:
Hello.

Having removed both front and rear guards for the summer I now want to refit them. Slightly concerned about securing the studs that go, vertically, into fixing holes. Don't want to over tighten and crack guards. Equally, don't want the bolts coming loose and rubbing on tyres. Is there a recommended torque? Would anyone use a thread-lock fluid to ensure secure fitting?

Thanks in anticipation.

Magnum3127

Danneaux:
On my old 8mm nutted through-bolts, I used thread-locker to keep them secure, but it has not been necessary since I upgraded my fleet with PlanetBike 10mm through-bolts with Nylock nuts (all stainless hardware). PB has a nice stock of reasonably priced spares they will mail for free domestically (US) because they feel it will allow repairs to be made to their existing products and so keep them out of the landfills. They also make dandy upgrades, along with their stainless fender (mudguard) stays in single- and v-configurations. See...
https://www.planetbike.com/service-parts-free-shipping/

I have to confess to replacing the Thorn supplied nuts, through-bolts and stays on my original Sherpa and later Nomad. Thorn did a superb job mounting them and nipping the ends flush with the cross-braces, but I prefer to have my 'guards adjustable depending on season and whether I anticipate a lot of rain and mud where I would like to allow extra clearance. Cutting and capping my stays so they allow at least 10-15mm of additional clearance has been really useful for me. In normal conditions, I draw them closer to the tires, leaving about 10-12mm clearance. When it is going to be messy, it is really nice to extend that, particularly at the bottom of the front mudguard where a lot of mud, muck, and debris tends to collect. Having a bit more clearance there allows the accumulation to drop off under its own weight when I hit a pothole.


--- Quote ---Don't want to over tighten and crack guards. Equally, don't want the bolts coming loose and rubbing on tyres.
--- End quote ---
I find holding the stay along its length with one hand below the nut/bolt assembly while I tighten the nut with the other hand keeps the cross-brace from torquing in the plastic mudguard, minimizing any possibility of cracking the blade where the bracket is riveted (the most common point of cracking). Conversely, I've see them crack when people got careless and just started cranking on the nuts which bows the stays slightly and pulls the brackets at an angle to the fender blade, causing stress at the rivets.


--- Quote ---Is there a recommended torque?
--- End quote ---
Mudguard strut nuts should be about 20-25 lb/in (2.3-2.9 Nm) according to this source, which correlates pretty well with my experience...
https://www.dedhambike.com/articles/torque-table-pg186.htm

Best wishes and good luck, Dan.

PH:
Dan's given a very thorough answer about the stays. but I thought the question was about the direct fitting of the guards to the frame and forks? I could be wrong, it does happen :o
For those direct fittings to fork and frame, fairly tight and using a bit of general purpose medium thread lock will help, though if you're going to make a habit of fitting and removing it can be a pain re-applying threadlock.
That's it really, unless you're a bit obsessive... Here's what I do, it's not a recommendation, but it keeps me happy and I don't have problems with them.
I use flange button head Torx screws, I use these for a few things so I have stock, the advantages are - The button head collects less dirt under the guard than a cap or hex head, the flange distributes the stress and the Torx head is less likely to round off than an alan head.  Also, with any M5 button head, you'll round it out before damaging the thread, and though you shouldn't do either, that one's an easier problem to deal with.
Something like these:
https://www.accu.co.uk/torx-flanged-button-screws/485122-SHBF-M5-14-A4?uk_google_shopping=1&c=3&gclid=EAIaIQobChMI9qDgoPPT-QIVhBCLCh06sgpQEAEYASABEgL9efD_BwE

Then I like to use a rubber washer between guard and frame, stops any rattling and protects paintwork, traditionally this would be a leather washer, but you don't get those in Wilco's.
I use both holes in the fork, I don't know why there's two, maybe its for choice or maybe it's just more secure, maybe someone who has has them fitted by Thorn will say what they do.  I find doing them both up tight distorts the shape of the guard a bit, so I use a couple of washers under one. I also like to use longish screws, longer than the gap between guard and tyre, in the unlikely event they both loosened the guard would be sat on the tyre but still attached to the fork. Frame fittings are a bit less safety critical, you'd have to loose both the chaistay and seatstay screws before it went anywhere.

mickeg:

--- Quote from: Magnum3127 on August 19, 2022, 09:51:02 pm ---...
Having removed both front and rear guards for the summer I now want to refit them. Slightly concerned about securing the studs that go, vertically, into fixing holes. Don't want to over tighten and crack guards. ...

--- End quote ---

I am not sure what you could crack.  I have some fenders that have plastic parts that could be cracked (have cracked a plastic part on a fender or mudguard on a Bontrager).

Could you elaborate on what you are afraid of damaging?  Photos help.

PH:

--- Quote from: mickeg on August 20, 2022, 02:26:06 am ---
--- Quote from: Magnum3127 on August 19, 2022, 09:51:02 pm ---I am not sure what you could crack.
--- End quote ---

I've seen quite a few examples of cracked chromoplastic guards, always at the fittings, never whilst being fitted, but sometimes after not a lot of use and nearly always guards that could IMO have been fitted better.
It is quite a rigid plastic, the key is for it not to be under strain, there's a very simple test to do for this - after fitting, remove and re-fit one fixed point at a time, the guard shouldn't move, each fixed point should be holding it there, not pulling it into place.
Or - treat them as a consumable and expect to replace every few years. 
--- End quote ---

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