SS bolts - loose

[BruKen]

There was a drop of oil on the garage floor. Shock horror.

I replaced all the crank and clutch cover cap head bolts with ss ones when rebuilding YAPI a couple years back. New gaskets too etc. Tonight I discovered every single one of them (that's like 20 plus plenty) was loose except the odd sized length bolts which I had to keep the originals in play. Were it not for that fact I'd say the gaskets had bedded in and the bolts just needed to be retorqued.

Any OCD or AR engineers out there that could explain this? It's a piece of info that would come in handy in the one upmanship, tyre kicking, baccy spitting contests held every weekend in the biker friendly pubs I roll past come weekends.

[Bixxer Bob]

Did you use copperslip when you installed them?  If so the dry torque figure is not enough.  but I've never found a formula for the required increase, just proved it in the lab. :roll:

[BruKen]

Yes I did. The rebuild showed terrible corrosion patterns. Hence the copper slip more than anything else.  Interesting.... thanks for that.

[BruKen]

Question: why didn't copperslip affect the standard bolts then. Just the ss ones. And not just some of them, every single one?

[JetdocX]

Did you use a calibrated torque wrench?

[BruKen]

For capheads? They are 12 Nm. That's finger tight and a quick nip and still wouldn't explain why only SS were affected. But full marks for being OCD and AR.

[Bixxer Bob]

Really just hypothesising because I can't inspect the bolts but stainless cuts smoother than mild steel - it's a joy to machine it, so maybe there's more grip on the standard bolts.  Also, I'm not familiar with how the bolts are made but based on my aircraft experience, the mild steel threads are likely to have been cut while the stainless are likely to have been rolled; again making them smoother.

The lab tests were on 1'' high tensile bolts with rolled threads from a T93 Radar. Still got one in the shed somewhere, along with 1'' rollers from a T91 main bearing and 3'' ball bearing from a T84.

[Mustang]

The oem bolts are flanged head hex bolts

 which have far superior holding power to covers and such

Flange Bolts
Flange bolts are identifiable by the ridge or skirt surrounding the bolt head. This skirt
acts as a means of distributing the clamping load of the bolt across the fastening
surface. A flange bolt is designed to provide the same holding power as a washer.

What do I win ?

[BruKen]

Win? Respect of your peers. But I'm not in a position to confirm if you or Bob is correct, or anyone else for that matter. However, as the practice of changing to SS cap heads and copper slip is common, it might well be worth routinely checking to see they haven't come loose. My LHS crank cover was one trip away from falling off and it was not obvious to a casual visual inspection because it was still adhering to the gasket, as were the bolts. Almost no threaded bite left at all. The clutch cover was only marginally better. Never seen this before in 25 years of biking.

[rybes]

hmmmmmmmmmm. n theres my bike with every nut n bolt in stainless. cant say ive ever had a problem but i feel like goin into the garage with me torque wrench  :lol:

[Nick Calne]

Guessing wildly but could the metal have slightly different thermal expansion properties leading to very slow but progressive loosening.

...I'll er... go now. :oops:

[BruKen]

That is not without some merit I'd suppose. Afterall the torque of a bolt is there to define its torsion isn't it?. And different alloys will stretch differently. Kind of reminds me of my sea days. Some of the engine mounting nuts were larger than me. To tighten them we would hydraulicly stretch the bolt and then wind the nut on. Release hydraulic tension and the bolt contracted pulling the nut tight. Thermal expansion could ultimately do the same thing. Though it must be said, the crank covers never get particularly hot.

Honest, I just don't know.

[rf9rider]

Bruken, i`ve always used ss bolts and screws, never had a problem with them coming loose, but then i`ve never copperslipped them, as i was under the impression stainless wouldn`t rot or rust, so threads would always be clean and always undo without a problem?

[BruKen]

Actually ss can rust a bugger in anaerobic conditions, ask any yachtsman with a ss mast. Also ss bolts don't stop corrosion, they just themselves are more resistant, the magnesium alloy still will experience galvanic corrosion and possibly more so than with steel bolts so the copperslip is more for their benefit.

http://www.mcnallyinstitute.com/04-html/4-1.html

However, I've never experienced ALL the bolts coming loose either. That's why I'm curious. It's not as though I don't have some experience in spanner twirling. I'm leaning towards Mustangs supposition. As Bob said, the bolts are rolled, the head is not perfectly flat as if milled, but slightly curved as if stamped. Looks beautiful, but probably lost some grip. I'll try some washers.... urrggg.... it looks so nice without lol.

[Mustang]

loctite blue ......done